Sample preparation induced artefacts in soft SAC solders from uncooled and cooled Argon ion milling

Sample preparation induced artefacts in soft SAC solders from uncooled and cooled Argon ion milling | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Sample preparation induced artefacts in soft SAC solders from uncooled and cooled Argon ion milling Charlotte Cui, Bernhard Sartory, Michael Reisinger, Peter Imrich, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7236642/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 21 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted 11 You are reading this latest preprint version Abstract Complex combinations of various materials in microelectronic packages pose challenges for sample preparation. Reliable cross-sectional sample preparation is critical for microstructural analysis, especially when utilising low-melting Sn‑Ag‑Cu (SAC) solders, which are easily deformed or damaged by mechanical grinding. Hence, this study explores the impact of femtosecond laser ablation for bulk material removal and subsequent Ar‑ion milling for final cross‑sectional polishing, comparing cooled and uncooled milling masks. We reveal that uncooled Ar-ion milling causes artefacts like increased surface roughness and fine Cu‑rich structures due to surface heating (~50 °C) combined with Cu redeposition on the preferentially milled, intruded SAC‑surface. Cryogenic cooling of the milling mask to -100 °C reduces these effects, minimising curtaining and preserving detail. However, cooled milling results in the displacement of recrystallised grains at grain boundaries due to the thermal expansion anisotropy of β-Sn. Thus, milling parameters must be carefully tailored to the desired preservation of microstructure, cracks and strain. Physical sciences/Engineering Physical sciences/Materials science Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Multimaterial, multicomponent packages are ubiquitous in power and microelectronics, wherein the electronic components are often joined by soldering with lowmelting, lowhardness metal alloys 1 – 4 . This complex combination of various materials in a single package poses challenges for its sample preparation for crosssectional microscopy, e.g. light optical microscopy or scanning electron microscopy (SEM) imaging. For instance, the inherently different stiffnesses of these materials may lead to damage of the sample during mechanical preparation, i.e. mechanical grinding and polishing 5 . Nonetheless, visualising the crosssectional microstructures of such multicomponent structures is vital for the analysis and understanding of material degradation and failure mechanisms 1 , 5 – 9 . Specifically, the visualisation of microstructural changes from thermomechanical fatigue in microelectronic solder balls, which interconnect chips with the printed circuit board (PCB), is vital since degradation of these interconnects may seriously impair their integrity and the functionality of the entire electronic device 3 , 5 , 6 . Lowmelting Sn – 3.0 wt.% Ag – 0.5 wt.% Cu (SAC305) solder alloys are commonly utilised for joining in microelectronic devices due to their nontoxicity 10 – 12 and processability 3 , 8 , 13 . The intermetallic precipitates Ag 3 Sn and Cu 6 Sn 5 , which form within the βSn matrix, increase the strength of the solder joint 14 . In order to further lower the liquidus temperature and simultaneously increase the strength of the SAC305 alloy, Bismuth (Bi) can be additionally alloyed 13 , 15 , 16 . Bi acts as solidsolution strengthener in the βSn matrix, if its additions are kept below the solubility limit of ~ 2.5 wt.% Bi 17 , 18 . Despite the various strengthening mechanisms, the βSn matrix of the solder alloy retains a relatively low hardness compared to the other materials in the multicomponent package 13 , 16 . This may lead to pronounced deformation or potential crack extension in the solder ball during mechanical crosssectional sample preparation. In order to minimise mechanical deformation during sample preparation, other material removal methods, such as laser ablation and ion beam milling can be utilised. However, potential heating effects from these preparation methods may impact the sample microstructure 19 – 24 . This may be a particular issue for lowmelting metals such as SAC305 alloys 13 , 24 – 26 . For laser ablation methods, heating effects may be reduced by laser pulsing with ultrashort pulse durations and low laser power 27 – 29 . By utilising laser pulse durations in the femtosecond (fs) range, the heat affected zone in metals is reportedly restricted to below 2 µm 30 , or more specifically, a few hundred nanometres 31 . Hence, ion milling methods may be subsequently applied to remove the heat affected zone. Contrary to laser ablation, common ion beam milling methods, including broad Argon (Ar) ion milling and focussed ion beam milling, do not involve pulsing. Hence, minimising sample heating can be achieved by reducing the kinetic energy of the impinging ions, i.e. their acceleration voltage, which reduces the energy that is transmitted to the sample 19 , 23 . By reducing the acceleration voltage, however, preparation time may increase significantly 19 , 22 . A different approach to counter sample heating due to ion impingement involves actively cooling the sample during milling 24 , 32 . The aim of this work is the evaluation of artefacts that may arise during crosssectional fslaser ablation and subsequent Arion milling for fieldemission SEM (FESEM) from thermomechanically fatigued lowmelting SAC305 + 1.1 wt.% Bi solder balls, which interconnect chips with PCBs. The crosssectional preparation of these solder balls is performed with fslaser prepreparation and final crosssectional Arion milling, utilising either cooled or uncooled ion milling masks. The application of an uncooled milling mask results in submicron Curich artefacts on the solder crosssection after Arion milling is performed. Moreover, pronounced surface roughness and curtaining around precipitates are observed. However, we illustrate, that these artefacts are effectively removed when the sample is milled with a cooled ion milling mask and otherwise identical milling parameters. Despite these microstructural artefacts on the sample crosssection, no significant precipitate coarsening from uncooled Arion milling is observed. Yet, the work also illustrates that inherent thermal expansion misfits during cooling and reheating may cause strain on the multimaterial sample. Thus, it is concluded that Arion milling temperature should be chosen based on the features that are investigated. Hence, we argue that actively cooled Arion milling seems to be more suitable for studies of smallscale microstructural features, whereas uncooled milling may be preferential for analyses of fatigue cracks and mechanical strain. Results Crosssectional sample preparation of lowhardness, lowmelting solder alloys in multicomponent microelectronic packages. The multimaterial, multicomponent structure of a representative microelectronic device, which is connected to the PCB by a complex arrangement of solder balls, is visualised in Fig. 1a via 3D Xray tomography. Due to the inherent difference in Xray attenuation by different materials, the individual electronic building blocks can be distinguished by their greyvalues and visualised accordingly. Therein, the polymer packaging of the chip is depicted in grey, chipmetallisations in blue, solder balls in silver, PCBmetallisations in orange, and the solder mask of the PCB in green. In order to prepare deformationfree sample crosssections from thermomechanically fatigued SAC305 + 1.1 wt.% Bi solder balls, neither mechanical sawing, grinding nor polishing is performed. Hence, all material removal is achieved by fslaser ablation and subsequent Arion milling. Specifically, prepreparation of the crosssections is achieved by bulk material removal utilising fslaser ablation, as schematically shown in Fig. 1b for one exemplary solder ball. The laser incidence is indicated in green and glass fibre reinforcements in the PCB are drawn as black lines. The prepreparation utilising a fslaser allows the fast removal of relatively large volumes, compared to ion milling methods. In order to achieve highquality crosssections for FESEM imaging, the final sample preparation is performed with broad Arion milling, schematically shown in Fig. 1c , wherein the direction of Arion impingement is indicated by pink arrows. During Arion milling, a metal mask, illustrated in black, is placed on top of the sample in order to define the location where the crosssection is milled and shield the rest of the sample from the impinging ion beam. Details about sample fabrication, thermomechanical fatigue, fslaser ablation and Arion milling are given in Methods . The complexity of the multimaterial, multicomponent package is further illustrated in Fig. 1d , which shows a FESEM backscatter electron (BSE) overview micrograph of its prepared crosssection. Again, the variety of materials in the micrograph can be discerned by their greyvalues due to masscontrast. The fslaser preprepared crosssection is marked by dashed green lines, whereas the final, Arion milled crosssection is not. Additional information regarding Xray tomography and FESEM imaging are provided in Methods . Microstructural artefacts on a solder ball crosssection prepared without actively cooling the Ar-ion milling mask. The final crosssectional sample preparation for FESEM imaging is performed utilising Arion milling, the milling parameters for which are given in Methods . Figure 2 shows micrographs of a representative solder ball after sample preparation without active cooling of the ion milling mask. FESEMBSE and secondary electron (SE) micrographs with increasing magnifications are shown in Fig. 2a and b , respectively. Figure 2 c and d illustrate the energy dispersive Xray spectroscopy (EDX) mapping of the largest magnification, ROI 2, for Cu and Ag, respectively. EDX signals of Sn and Bi are provided in Supplementary Fig. 1 . Crystallographic information about ROI 2 is provided in Fig. 2e , wherein its electron backscatter diffraction (EBSD) phase mapping is shown. Therein, βSn is shown in blue, Cu 6 Sn 5 in yellow and Ag 3 Sn in red. EBSD inverse pole figure (IPF) and phase mappings of the entire solder ball are provided in Supplementary Fig. 2 . Details about FESEM imaging, as well as EDX and EBSD mapping are provided in Methods . Figure 2 shows that, in addition to larger Ag 3 Sn and Cu 6 Sn 5 precipitates, fine, Curich lines are present on the crosssection. These lines are especially apparent in the BSE micrographs of ROI 1 and 2 in Fig. 1a and the EDX mapping of ROI 2 in Fig. 1c . An additional crosssection prepared with the same ion milling parameters is shown in Supplementary Fig. 3 . Those FESEMBSE micrographs in Supplementary Fig. 3a exhibit similar lines within the βSn grains, as well as thicker ones along the grain boundaries in ROI B. Given the needle shape of the Curich agglomerations, dotted areas on the FESEM crosssections would suggest Cuneedle growth away from the crosssection, i.e. into the solder ball bulk. In order to investigate, whether these needles are also present in the bulk material, a lamella liftout for scanning transmission electron microscopy (STEM) is performed in such a Curich dotted region, see Supplementary Fig. 4 . However, the corresponding STEM bright field (BF) micrographs and STEMEDX mappings in Supplementary Fig. 4b only exhibit two Curich dots at the crosssection surface, while the rest of the lamella is homogeneous. This finding shows that the Curich agglomerations only form on the surface of the Arion milled crosssection, suggesting that they are artefacts from the preparation. Moreover, the SE micrographs in Fig. 1b and Supplementary Fig. 3b visualise a pronounced, periodic surface roughness. Supplementary Fig. 3b also shows pronounced curtaining originating from Ag 3 Snprecipitates. Microstructure of a crosssection prepared utilising an actively cooled Ar-ion milling mask. In the following, we investigate whether and how the microstructure of the lowmelting SAC305 + 1.1 wt.% Bi solder alloy is affected by Arion milling with an actively cooled milling mask. We utilise the same Arion milling parameters as for the previous milling with the uncooled milling mask, only that the milling mask is actively cooled to -100°C. Details are given in Methods . Figure 3 depicts FESEM micrographs of a representative solder ball that is prepared with an actively cooled ion milling mask. Micrographs of an additional solder ball prepared in the same way are shown in Supplementary Fig. 7 . Figures 3 a and b show increasing magnifications of FESEMBSE and SE micrographs, respectively. The largest magnification, ROI 4, is mapped utilising EDX. The respective Cu and AgEDX mappings are shown in Fig. 3c and d , Sn and BiEDX mappings in Supplementary Fig. 5 . Moreover, the EBSDphase mapping of ROI 4 is shown in Fig. 3e , wherein βSn is coloured blue, Cu 6 Sn 5 yellow and Ag 3 Sn red. EBSDIPF and phase mappings of the entire solder ball are depicted in Supplementary Fig. 6 . Contrary to the micrographs from uncooled preparation in Fig. 2 , Fig. 3 and Supplementary Fig. 6 show that no Curich lines are visible in the micrographs after actively cooled Arion milling. Furthermore, both surface roughness and curtaining around precipitates are reduced significantly, which is evident from the SEmicrographs in Fig. 3b and Supplementary Fig. 7b . Insitu temperature measurement during Arion milling without active cooling. In order to quantitatively evaluate the temperaturerise during Arion milling, an insitu temperature measurement setup is built, schematically shown in Fig. 4a . A vacuum flange with a thermocouple feedthrough is machined and mounted onto the ion milling system, connecting the sample inside the vacuum chamber with a multimeter on the outside. From the multimeter, the temperature of the thermocouple inside the vacuum chamber can be read. Figure 4 b depicts the fixture of the thermocouple on the sample. One row of solder balls is separated from the microelectronic package utilising fslaser ablation and placed on a Siwafer piece, in order to ensure the thermocouple can be placed as close to the Arion milling area as possible. Thus, the thermocouple is placed between the ion milling mask and the sample on the Siwafer piece, and fixed utilising conductive silver paste. Hence, it provides temperature readings directly from the Arion milling area. Arion milling is performed with the same acceleration voltage as the previous millings, but the sample stage is not swung, as not to break the fixture of the thermocouple. Figure 4 c shows the temperature profile that is measured during Arion milling utilising these parameters. The temperature increases rapidly to 40°C at the beginning of milling and saturates at 50°C after ~ 2 hours. A light optical image of the crosssection after milling is depicted in Fig. 4d . The chip and PCBmetallisations are discernible due to their Cucolouration. Microstructural Differences: Scrutinising potential precipitate coarsening and thermal expansion anisotropy. Further, due to the temperature rise during uncooled Arion milling and due to the microstructural differences between crosssections prepared with and without active cooling, potential precipitate coarsening during the sample preparation without active cooling is studied. To that end, Ag and CuEDX mappings of ROI 2 and ROI 4 are comparatively analysed and mean equivalent precipitate radii are calculated, the results of which are shown in Fig. 5 . The contours of the precipitates which are included in the analysis are drawn in yellow and the mean equivalent radii, as well as standard deviations, are printed on the top of each contour image. For the analysis of the CuEDX mapping of ROI 2, the lineshaped enrichments are excluded from the evaluation. Details about image processing and radii calculations are provided in Methods . The quantitative precipitate size analyses in Fig. 5 reveal no precipitate coarsening in ROI 2 from uncooled crosssectional Arion milling compared to ROI 4, since the mean equivalent precipitate radii of both Ag 3 Sn and Cu 6 Sn 5 lie within the standard deviations of the respectively other preparation method. Although actively cooled Arion milling produces Cu artefactfree SAC crosssections with reduced curtaining and surface roughness, issues arise in some parts of the crosssection when the sample is reheated to room temperature after milling. Figure 6 depicts FESEM micrographs of the solder ball from Fig. 3 , which is milled utilising an actively cooled milling mask. Displacements along grain boundaries are discernible in the FESEMSE micrograph in Fig. 6a and especially in the detail of ROI 5 shown in Fig. 6b . The EBSDIPF mapping in Fig. 6c confirms that the displacement of recrystallised βSn grains occurs along grain boundaries. These displacements may arise after cooled Arion milling at -100°C, when the sample is reheated. Therein, previously recrystallised grains may expand to different extents due to the large thermal expansion anisotropy of βSn 1 , 33 – 35 , leading to discontinuities on the Arion polished free surface. Discussion Reliable, artefactfree sample preparation for microstructural imaging is crucial for the indepth understanding of material properties and behaviour. However, crosssectional sample preparation of multicomponent, multimaterial stacks, such as microelectronic packages, poses challenges due to the inherent differences in stiffness, hardness and sputter yield of the various materials. Therein, particular care needs to be taken for the crosssectional preparation of lowhardness, lowmelting SACsolder balls 1 – 4 , which are sandwiched between the chip and the PCB in microelectronic boardlevel packages. Hence, these solder balls are not directly accessible for crosssectional imaging methods and multiple additional components of the package need to be considered during the preparation of crosssections. Because of the comparably low hardness of the βSn matrix 13 , 16 , crosssectional mechanical grinding and polishing of the device may lead to deformation of the SACsolder balls. Moreover, thermomechanically cycled solder balls may exhibit fatigue cracks 1 , 5 – 9 , 36 – 38 , which could be extended during mechanical preparation. Therefore, this study seeks to optimise the crosssectional sample preparation of such multicomponent devices, which include lowmelting components, for SEM imaging utilising fslayer ablation and Arion milling. H4erein, fslaser ablation is utilised for the removal of large sample volumes and the final sample crosssection is polished utilising Arion milling. Since Arion milling is the last preparation step, potential heating effects in the process may affect the microstructure of the lowmelting SACsolder joint that interconnects the microelectronic components. Such artefacts are shown in Fig. 2a and c , Supplementary Fig. 1 and Supplementary Fig. 3 . Fine Curich structures form on the SAC crosssection during uncooled Arion milling. However, these structures only form on the surface of the Arion milled crosssection, as shown with STEMEDX in Supplementary Fig. 4. Moreover, these Curich structures are not present on crosssections that are prepared with a cryogenically cooled ion milling mask, as depicted in Fig. 3a and c , Supplementary Fig. 5 and Supplementary Fig. 7 , which indicates a temperaturedependency of the formation of these Curich structures. Insitu temperature measurement, shown in Fig. 4 , reveals a temperatureincrease up to 50°C during uncooled Arion milling. However, this temperatureincrease during Arion milling does not cause precipitate coarsening of neither Ag 3 Sn nor Cu 6 Sn 5 , as Fig. 5 illustrates. Hence, the Arion induced heating may not suffice for precipitate coarsening, but the results suggest that the temperatureincrease on the SAC surface plays a crucial role for artefactfree crosssectional preparation. Supplementary Fig. 8a and b show laser confocal surface profiles in the directions of Arion milling utilising uncooled and cooled milling masks. These crosssections correspond to those depicted in Fig. 2 and Fig. 3 , respectively. Both surface profiles reveal that the SACsolder ball surface is intruded, compared to the Cu metallisations on both chipand PCBside, indicating that the SACsolder ball is milled preferentially. Similar observations of preferential ion milling of SACalloys are made in 24 . Considering that the multimaterial stack is milled from chip to PCB, as sketched in Fig. 1b , the SACsolder ball is already milled when the Arion beam reaches the PCBCu metallisation. Hence, Cu that is subsequently milled from the PCBmetallisation is redeposited onto the solder ball 39 and cannot be removed thereafter, since the SAC crosssection is intruded with respect to the chip and the ion milling mask. However, the absence of the Curich structures on the crosssections that are actively cooled during Arion milling, see Fig. 3 and Supplementary Fig. 7 , suggests that they only form at elevated surface temperatures, which are shown to reach up to 50°C during uncooled milling, see Fig. 4 . Therefore, the formation of Curich structures may be suppressed at -100°C when Arion milling is performed utilising an actively cooled mask. It should be noted that thicker Curich structures in Fig. 2d are indexed as Cu 6 Sn 5 in the EBSDphase mapping. In the field of metallic thinfilms, ion bombardment has proven to be a useful tool for the fabrication of selforganised micro and nanopatterns 40 , 41 . Moreover, monolayers and thin films have been shown to change their morphologies when the substrate temperatures are varied during deposition 42 – 44 . Hence, the assembly of resputtered Cu from the PCBmetallisation into lineshaped Cu 6 Sn 5 on the SACsolder crosssection may be facilitated by Arion bombardment, combined with surface migration at 50°C. The distinctly lineshaped morphology of the Curich structures and their presence along βSn grain boundaries in Supplementary Fig. 3 may indicate preferred formation of Cu 6 Sn 5 in certain areas on the solder ball surface. Cu that is resputtered onto the solder ball crosssection may migrate towards areas with higher energies, where Cu 6 Sn 5 formation could be preferential. Both surface migration of Cu and Cu 6 Sn 5 phase formation may be hindered at -100°C, which could explain the absence of these structures after actively cooled Arion milling. In addition to the absence of these fine Curich structures, the surface roughness of the βSn matrix decreases visibly when the ion milling mask is actively cooled, compared to the preparation with an uncooled mask. This effect is discernible when comparing Fig. 2b with Fig. 3b . The suppression of this surface artefact may stem from the suppression of surface migration of vacancies and adatoms 40 , 45 , 46 . Furthermore, curtaining artefacts around precipitates, discernible in Supplementary Fig. 3 , are minimised with active cooling of the ion milling mask, which may be attributed to a decrease of sputtering yield of the βSn matrix at -100°C, as observed in 24 . Despite its advantages regarding the suppression of Curich artefacts and decreased surface roughness, actively cooled Arion milling poses one disadvantage. As discernible in Fig. 6 , individual βSn grains are displaced along grain boundaries after actively cooled Arion milling. In addition, the surface profile of the crosssection in Supplementary Fig. 8b , which is milled with an actively cooled mask, shows that recrystallised grains are elevated compared to the rest of the singlecrystalline solder ball. The displacement of recrystallised grains may be exacerbated by the high thermal expansion anisotropy of βSn 1 , 9 , 33 , 34 , but should be especially considered for the preparation of multicomponent, multimaterial stacks, since the inherently different thermal expansion coefficients may cause substantial misfit stresses during cooling and reheating of the sample 3 , 35 – 37 , 47 . In summary, microstructural artefacts in lowmelting SACsolder balls stemming from Arion milling of multicomponent microelectronic devices are evaluated. Both surface roughness and veridical presentation of microstructural features are improved by actively cooled Arion milling. However, misfit stresses may arise during actively cooled Arion milling due to thermal expansion misfits. Hence, special care needs to be taken for the preparation of multimaterial samples. Therefore, Arion milling temperature should be chosen based on the features that are studied. For the investigation of small microstructural features, actively cooled Arion milling may be preferential, whereas uncooled Arion milling may be more suitable the evaluation of strains and crack propagation. Methods Sample material and geometry. The investigated solder balls are produced by droplet spraying in an inert N2 atmosphere and subsequently soldered between the Cu‑metallisations of the chip and the PCB. Reflow is done at a peak temperature of 240 °C and with a mean heating rate of 44 °C/min in inert N2 atmosphere, followed by rapid air cooling to 90 °C with a mean cooling rate of 107 °C/min and ambient air cooling to room temperature. The investigated SAC305 + 1.1 wt.% Bi sample is thermally cycled 2914 times between -40 – 125 °C with ramp‑ and dwell‑times of 15 mins, respectively. 3D X ray tomography. A 3D X ray tomography scan of a representative BGA is done utilising a GE Phoenix Nanotom M (research edition) with 110 kV acceleration voltage, 120 µA tube current and a cone‑beam. By utilising a cone‑beam, the achievable spatial resolution is dependent on the lateral sample size (~ 10 x 7 mm 2 ). For the investigated sample, this results in a voxel size of 5.33 x 5.33 x 5.33 µm 3 . The different building blocks of the device, i.e. the chip, solder balls and the PCB are distinguishable due to their various grey‑values and reconstructed utilising VGSTUDIO MAX. Sample preparation. A 3D Micromac microPREP PRO FEMTO fs‑laser with a laser power of 300 mW is used to pre‑prepare the cross‑sections for FESEM. This laser has a wavelength of 515 nm and a pulse length of less than 300 fs. The final cross‑sections for FESEM imaging are prepared utilising Ar‑ion milling. Uncooled Ar‑ion milling is done with a Hitachi IM4000+ ion milling system. The accelerating voltage for ion slicing is set to 6 kV and the swing angle to 30° with 3 swings per minute. Ar‑ion milling with the actively cooled mask is done with a Hitachi IM5000+ ion milling system, utilising the same milling parameters and cooling the ion milling mask to ‑100 °C. FESEM imaging. The FESEM‑BSE and ‑SE micrographs are acquired with a Zeiss Crossbeam 550 FESEM utilising an acceleration voltage of 3 kV and sample currents of 3 nA. The EDX mappings are done utilising an Oxford Ultim Extreme detector. The EBSD maps are acquired with an accelerating voltage of 20 kV, a step size of 400 nm and an Oxford Symmetry S3 detector. Oxford Instruments AZtec 6.2. is utilised for the EDX and EBSD analyses. Precipitate size analysis. In order to determine, whether the heating from Ar‑ion milling causes precipitate coarsening when the milling mask is not actively cooled, the Ag 3 Sn‑ and Cu 6 Sn 5 ‑precipitate sizes are evaluated and compared to those after utilising a cooled mask. The calculations of the mean equivalent Ag 3 Sn‑ and Cu 6 Sn 5 ‑precipitate radii in Fig. 5 are done based on the Ag‑ and Cu‑EDX mappings of ROI 2 and ROI 4, shown in Supplementary Fig. 2 and 6 , respectively. To that end, the respective EDX mappings are binarily thresholded and the contours are detected. In order to exclude the Cu‑rich, line‑shaped artefacts in ROI 2 from the analysis, limits are set for the areas and aspect‑ratios of the detected contours. Finally, the contour areas are evaluated and their equivalent radii are calculated. The results of these analyses are shown in Fig. 4 . The analysis is done with Python 3.8.13, OpenCV 4.0.1 and numpy 1.22.3. For the visualisation, matplotlib 3.5.1 is utilised. Declarations Competing interests The authors declare no competing interests. Correspondence and requests for materials should be addressed to R.B. Data availability The data that support the findings of this study are available from the corresponding author upon reasonable request. Code availability All code that support the findings of this study are available from the corresponding author upon reasonable request. Author contributions C.C. did the image-analysis work, data interpretation and evaluation under the supervision of R.B.; C.C. and B.S. performed the in‑situ temperature measurement in discussion with R.B.; W.H. fabricated and provided the samples, with support from M.R. and P.I; C.C., B.S. and R.B. planned the FESEM‑BSE, EDX and EBSD; C.C. and R.B. wrote the paper; All authors discussed the results and commented on the paper. Acknowledgement We acknowledge the support from J. Rosc for the X ray tomography scan, K. Fischak for the SEM, EDX and EBSD measurements, L. Schieder for the actively cooled Ar‑ion milling, M. Burtscher and D. Kiener for the STEM‑BF and STEM‑EDX measurements and M. Tkadletz for the laser confocal profiling. Funding Declaration The authors gratefully acknowledge the financial support under the scope of the COMET program within the K2 Center “Integrated Computational Material, Process and Product Engineering (IC-MPPE)” (Project No 886385). 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Microelectronics Reliability 119, 114065 (2021). Huang, M. L. & Wang, L. Effects of Cu, Bi, and In on microstructure and tensile properties of Sn-Ag-X(Cu, Bi, In) solders. Metall and Mat Trans A 36, 1439–1446 (2005). Hirayama, Y. & Obara, M. Heat-affected zone and ablation rate of copper ablated with femtosecond laser. Journal of Applied Physics 97 (2005). Stuart, B. et al. Optical ablation by high-power short-pulse lasers. Optical Society of America, 459–468 (1996). Hirayama, Y. & Obara, M. Heat effects of metals ablated with femtosecond laser pulses. Applied Surface Science, 741–745 (2002). Le Harzic, R. et al. Comparison of heat-affected zones due to nanosecond and femtosecond laser pulses using transmission electronic microscopy. Applied Physics Letters 80, 3886–3888 (2002). Bonse, J. & Krüger, J. Probing the heat affected zone by chemical modifications in femtosecond pulse laser ablation of titanium nitride films in air. Journal of Applied Physics, 54902 (2010). Kim, S.-H., El-Zoka, A. A. & Gault, B. A Liquid Metal Encapsulation for Analyzing Porous Nanomaterials by Atom Probe Tomography. Microsc Microanal, 1198–1206 (2022). Deshpande, A., Jiang, Q. & Dasgupta, A. Effect of Microscale Heterogeneities and Stress State on the Mechanical Behavior of Solder Joints. In 2020 19th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm) (IEEE2020), 1024–1028. Zhou, B., Bieler, T. R., Lee, T. & Liu, K.-C. Crack Development in a Low-Stress PBGA Package due to Continuous Recrystallization Leading to Formation of Orientations with [001] Parallel to the Interface. Journal of Elec Materi 39, 2669–2679 (2010). Matin, M. A., Vellinga, W. P. & Geers, M. Thermomechanical fatigue damage evolution in SAC solder joints. Materials Science and Engineering: A 445-446, 73–85 (2007). Bieler, T. R. et al. The Role of Elastic and Plastic Anisotropy of Sn in Recrystallization and Damage Evolution During Thermal Cycling in SAC305 Solder Joints. Journal of Elec Materi 41, 283–301 (2012). M. Brunnbauer, T. Meyer, G. Ofner, K. Mueller, R. Hagen. Embedded Wafer Level Ball Grid Array (eWLB). 33rd International Electronics Manufacturing Technology Conference, 1–6 (2008). Mazánová, V., Heczko, M. & Polák, J. On the mechanism of fatigue crack initiation in high-angle grain boundaries. International Journal of Fatigue 158, 106721 (2022). Müller, K. P. & Pelka, J. Redeposition in ion milling. Microelectronic Engineering, 91–101 (1987). Kratzer, M. et al. Fabrication of ion bombardment induced rippled TiO2 surfaces to influence subsequent organic thin film growth. Journal of physics. Condensed matter : an Institute of Physics journal 30, 283001 (2018). Kumar, M. et al. Roughening and sputtering kinetics of Pt thin films at different angles of ion irradiation. Materials Letters 303, 130474 (2021). Röder, H., Brune, H., Bucher, J. P. & Kern, K. Changing morphology of metallic monolayers via temperature controlled heteroepitaxial growth. Surface Science, 121–126 (1993). Jungyoon, E. et al. Effects of substrate temperature on copper(II) phthalocyanine thin ®lms. Applied Surface Science, 274–279 (2003). Kaiser, N. Review of the fundamentals of thin-film growth. Applied Optics, 3053–3060 (2002). Bradley, R. M. & Harper, J. M. E. Theory of ripple topography induced by ion bombardment. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 6, 2390–2395 (1988). Karmakar, P. & Ghose, D. Ion beam sputtering induced ripple formation in thin metal films. Surface Science 554, L101-L106 (2004). Kariya, Y., Williams, N., Gagg, C. & Plumbridge, W. Tin pest in Sn-0.5 wt.% Cu lead-free solder. JOM 53, 39–41 (2001). Additional Declarations No competing interests reported. Supplementary Files Supplementary.pdf Cite Share Download PDF Status: Published Journal Publication published 21 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 04 Sep, 2025 Reviews received at journal 03 Sep, 2025 Reviews received at journal 30 Aug, 2025 Reviewers agreed at journal 26 Aug, 2025 Reviewers agreed at journal 25 Aug, 2025 Reviewers agreed at journal 09 Aug, 2025 Reviewers invited by journal 04 Aug, 2025 Editor invited by journal 04 Aug, 2025 Editor assigned by journal 31 Jul, 2025 Submission checks completed at journal 30 Jul, 2025 First submitted to journal 28 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7236642","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":495923817,"identity":"c8539a25-ab5c-4590-a1a7-1d847ef23bdb","order_by":0,"name":"Charlotte Cui","email":"","orcid":"","institution":"Materials Center Leoben Forschung GmbH","correspondingAuthor":false,"prefix":"","firstName":"Charlotte","middleName":"","lastName":"Cui","suffix":""},{"id":495923819,"identity":"7c702259-5f88-49f5-a035-d049bd7e2351","order_by":1,"name":"Bernhard Sartory","email":"","orcid":"","institution":"Materials Center Leoben Forschung GmbH","correspondingAuthor":false,"prefix":"","firstName":"Bernhard","middleName":"","lastName":"Sartory","suffix":""},{"id":495923821,"identity":"0dbc8975-40ef-4c4d-8726-656997bd9c81","order_by":2,"name":"Michael Reisinger","email":"","orcid":"","institution":"Kompetenzzentrum für Automobil- und Industrieelektronik GmbH","correspondingAuthor":false,"prefix":"","firstName":"Michael","middleName":"","lastName":"Reisinger","suffix":""},{"id":495923823,"identity":"8afe5707-00b7-4069-8588-d3406bcda2c8","order_by":3,"name":"Peter Imrich","email":"","orcid":"","institution":"Kompetenzzentrum für Automobil- und Industrieelektronik GmbH","correspondingAuthor":false,"prefix":"","firstName":"Peter","middleName":"","lastName":"Imrich","suffix":""},{"id":495923824,"identity":"0a21c590-2487-4af6-ad1d-e72364683cf9","order_by":4,"name":"Walter Hartner","email":"","orcid":"","institution":"Infineon Technologies AG","correspondingAuthor":false,"prefix":"","firstName":"Walter","middleName":"","lastName":"Hartner","suffix":""},{"id":495923825,"identity":"0c9997a2-9376-4dee-a420-6f87403c74a2","order_by":5,"name":"Roland Brunner","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIiWNgGAWjYFAC5gYGBjaGBCjPhoGBnaAWRhQtaUAzgNQBErQcJqzFvL2x8XNBGUOe+YzcYw8+7jkfzd/MwPj5Ax4tMmcONkvPOMdQLHMjL91wxrPbuTMOMzBL4LNFQiKxQZq3jSFxhkSOmTTPgdu5G4AOI6Sl+Tdcy58D50BamH8Q0NKGsIXhwAGQFjb8tvAcbLPmOSdRLMHzxkyy50Ay0C+MbRZn8Glhbz58m6fMJk+CPcdM4scBu9z+9ubDNyrwaIHpROaAYmoUjIJRMApGAUUAAOPbSWGjmh3iAAAAAElFTkSuQmCC","orcid":"","institution":"Materials Center Leoben Forschung GmbH","correspondingAuthor":true,"prefix":"","firstName":"Roland","middleName":"","lastName":"Brunner","suffix":""}],"badges":[],"createdAt":"2025-07-28 18:38:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7236642/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7236642/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-25169-z","type":"published","date":"2025-11-21T15:57:08+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":88439957,"identity":"cae92d7e-cc0c-459a-bb0a-f0b0ddee727f","added_by":"auto","created_at":"2025-08-06 12:33:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":5304471,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic sample preparation workflow for FESEM, sample geometry and exemplary cross‑section.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSample and preparation overview. \u003cstrong\u003ea\u003c/strong\u003e The geometry of the sample is visualised by 3D X-ray tomography, in order to show its complexity. The polymer packaging of the chip is shown in grey, the chip‑metallisations in blue, the PCB‑metallisations in orange, the solder mask of the PCB in green and the solder balls in silver. The entire device is shown in the upper half, whereas the polymer is hidden in the lower half. Additionally, the chip‑metallisation is hidden in the right half of the 3D X-ray tomography scan. \u003cstrong\u003eb\u003c/strong\u003e Schematic fs‑laser pre‑preparation of the multi‑material, multi‑component sample. The fs‑laser is schematically shown in green. The multi‑material, multi‑component structure is sketched. The same colour code as in \u003cstrong\u003ea\u003c/strong\u003e is utilised. Glass fibres in the PCB are shown as black lines.\u003cstrong\u003e c\u003c/strong\u003e Schematic final cross‑sectional preparation for FESEM utilising Ar‑ion beam milling. The direction of Ar‑ion incidence is indicated by pink arrows and the ion milling mask is sketched in black. \u003cstrong\u003ed\u003c/strong\u003e Exemplary FESEM‑BSE micrograph of the sample cross‑section after fs‑laser pre‑preparation and Ar‑ion milling. The area that is only fs‑laser ablated and unaffected by Ar‑ion milling is marked by dashed green lines. The multi‑material stack is discernible by the various grey‑values due to mass‑contrast.\u003c/p\u003e","description":"","filename":"Figure1SchematicsamplepreparationworkflowforFESEMsamplegeometryandexemplarycrosssection.png","url":"https://assets-eu.researchsquare.com/files/rs-7236642/v1/2173b7ea6609d0890376a2bb.png"},{"id":88439660,"identity":"ba880647-4c07-4e7c-ab76-595f0041ac74","added_by":"auto","created_at":"2025-08-06 12:25:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":6180997,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExemplary Ar‑ion milled FESEM cross‑section utilising an uncooled ion milling mask.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCross‑sectional microstructure of an exemplary SAC305\u0026nbsp;+\u0026nbsp;1.1\u0026nbsp;wt.%\u0026nbsp;Bi solder ball prepared with an uncooled mask. ROIs\u0026nbsp;1 and 2 illustrate more detailed micrographs, respectively. \u003cstrong\u003ea\u003c/strong\u003e\u0026nbsp;From left to right: FESEM‑BSE micrographs with increasing magnifications. Various phases can be distinguished by their mass‑contrast. \u003cstrong\u003eb\u003c/strong\u003e\u0026nbsp;From left to right: FESEM‑SE micrographs with increasing magnifications. Surface roughness is discernible by varying grey‑values. \u003cstrong\u003ec\u003c/strong\u003e\u0026nbsp;Cu‑EDX\u0026nbsp;mapping of ROI\u0026nbsp;2. \u003cstrong\u003ed\u003c/strong\u003e\u0026nbsp;Ag‑EDX mapping of ROI\u0026nbsp;2.\u0026nbsp; \u003cstrong\u003ee\u003c/strong\u003e EBSD‑phase\u0026nbsp;mapping of ROI\u0026nbsp;2, showing β‑Sn\u0026nbsp;(blue), Ag\u003csub\u003e3\u003c/sub\u003eSn\u0026nbsp;(red) and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e\u0026nbsp;(yellow).\u003c/p\u003e","description":"","filename":"Figure2ExemplaryArionmilledFESEMcrosssectionutilisinganuncooledionmillingmask.png","url":"https://assets-eu.researchsquare.com/files/rs-7236642/v1/7e7366dd7f524a12189b4c51.png"},{"id":88439663,"identity":"a949564e-0200-4f08-983c-c55d75219e54","added_by":"auto","created_at":"2025-08-06 12:25:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":5873980,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExemplary Ar‑ion milled FESEM cross‑section utilising an actively cooled ion milling mask.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCross‑sectional microstructure of a representative SAC305\u0026nbsp;+\u0026nbsp;1.1\u0026nbsp;wt.%\u0026nbsp;Bi solder ball prepared with a cooled ion milling mask. ROIs\u0026nbsp;3 and 4 illustrate more detailed micrographs, respectively. \u003cstrong\u003ea\u003c/strong\u003e\u0026nbsp;From left to right: FESEM‑BSE micrographs with increasing magnifications. Various phases can be distinguished by their mass‑contrast. \u003cstrong\u003eb\u003c/strong\u003e\u0026nbsp;From left to right: FESEM‑SE micrographs with increasing magnifications. Surface roughness is discernible by varying grey‑values. \u003cstrong\u003ec\u003c/strong\u003e\u0026nbsp;Cu‑EDX\u0026nbsp;mapping of ROI\u0026nbsp;4. \u003cstrong\u003ed\u003c/strong\u003e\u0026nbsp;Ag‑EDX\u0026nbsp;mapping of ROI\u0026nbsp;4. \u003cstrong\u003ee\u003c/strong\u003e\u0026nbsp;EBSD‑phase\u0026nbsp;mapping of ROI\u0026nbsp;4, depicting the locations of β‑Sn\u0026nbsp;(blue), Ag\u003csub\u003e3\u003c/sub\u003eSn\u0026nbsp;(red) and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e\u0026nbsp;(yellow).\u003c/p\u003e","description":"","filename":"Figure3ExemplaryArionmilledFESEMcrosssectionutilisinganactivelycooledionmillingmask.png","url":"https://assets-eu.researchsquare.com/files/rs-7236642/v1/bf65a64965ee74181a238282.png"},{"id":88439664,"identity":"2c7dd8fe-ee06-4301-9ec7-0d43cf2b1e64","added_by":"auto","created_at":"2025-08-06 12:25:36","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1736778,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExperimental setup for in‑situ temperature measurement.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn‑situ temperature measurement during Ar‑ion milling. a Schematic experimental setup. The vacuum chamber of the ion milling system is represented by the blue box. The Ar‑ion gun is indicated on the left sidewall of the vacuum chamber and the emitted Ar‑ion beam is depicted as a pink arrow, impinging on the ion milling mask. The sample, which is situated under the ion milling mask, is illustrated in green. The grey block beneath the sample represents the sample holder. The thermocouple is attached to the sample and fed through a vacuum flange, sketched beneath the Ar‑ion gun. Outside the vacuum chamber, the thermocouple is plugged into a multimeter where the temperature during Ar‑ion milling can be read in‑situ. The direction of view is indicated by the grey arrow. \u003cstrong\u003eb\u003c/strong\u003e Top‑view of the thermocouple fixture between sample and ion milling mask before Ar‑ion milling. The thermocouple is fixed utilising conductive silver paste. \u003cstrong\u003ec\u003c/strong\u003e In‑situ temperature profile during Ar‑ion milling utilising an acceleration voltage of 6 kV without swinging the sample holder. \u003cstrong\u003ed\u003c/strong\u003e Top‑view image after Ar‑ion milling. The thermocouple and silver paste are indicated, as well as the chip‑metallisation, solder ball and PCB‑metallisation in the sample\u003c/p\u003e","description":"","filename":"Figure4Experimentalsetupforinsitutemperaturemeasurement.png","url":"https://assets-eu.researchsquare.com/files/rs-7236642/v1/9b3a1aa2b96c559cd2c27c4f.png"},{"id":88439960,"identity":"3436d876-d689-4c12-96ec-cc6dc2b8be10","added_by":"auto","created_at":"2025-08-06 12:33:36","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":6205791,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePrecipitate size analysis after cross‑sectional Ar‑ion milling with cooled and uncooled masks based on EDX\u0026nbsp;mappings.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAg\u003csub\u003e3\u003c/sub\u003eSn‑ and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e‑precipitate size analysis after cross‑sectional Ar‑ion milling utilising an uncooled and cooled mask, respectively. The analysis is done for the Cu‑ and Ag‑EDX mappings of ROI\u0026nbsp;2 on the uncooled cross‑section, see \u003cstrong\u003eFig.\u0026nbsp;2c, d\u003c/strong\u003e, and ROI\u0026nbsp;4 on the cooled cross‑section, see \u003cstrong\u003eFig.\u0026nbsp;3c, d\u003c/strong\u003e. The first row shows the Ag‑EDX mappings and their contrast images overlaid with the thresholded contours of ROI\u0026nbsp;2 and ROI\u0026nbsp;4, respectively. The second row shows the same for the Cu‑EDX mappings. The analysed contours are illustrated in yellow. The mean equivalent precipitate radii are printed in the top left corners of each contrast image. Scalebar of 3\u0026nbsp;µm is valid for all images.\u003c/p\u003e","description":"","filename":"Figure5PrecipitatesizeanalysisaftercrosssectionalArionmillingwithcooledanduncooledmasksbasedonEDXmappings.png","url":"https://assets-eu.researchsquare.com/files/rs-7236642/v1/ddaf11df3e53f2a46a8417fa.png"},{"id":88439959,"identity":"0f363a96-6e9b-43bf-97ec-dda63804234d","added_by":"auto","created_at":"2025-08-06 12:33:36","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1805137,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDisplacement of recrystallised grains along grain boundaries after actively cooled Ar‑ion milling.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSolder ball cross‑section from \u003cstrong\u003eFig. 3\u003c/strong\u003e, wherein individual grains are visibly displaced after actively cooled Ar‑ion beam milling. \u003cstrong\u003ea\u003c/strong\u003e Overview SE micrograph, \u003cstrong\u003eb\u003c/strong\u003e detailed SE micrograph of ROI 5, marked in \u003cstrong\u003ea\u003c/strong\u003e. \u003cstrong\u003ec\u003c/strong\u003e Overview EBSD‑IPF mapping. Scalebars of 100 µm and 10 µm are valid for the overview and detail micrographs, respectively.\u003c/p\u003e","description":"","filename":"Figure6DisplacementofrecrystallisedgrainsalonggrainboundariesafteractivelycooledArionmilling.png","url":"https://assets-eu.researchsquare.com/files/rs-7236642/v1/87bed284b25192463ebf8a8a.png"},{"id":96650286,"identity":"c45c4e67-7d89-4858-bbb7-02b2731658e8","added_by":"auto","created_at":"2025-11-24 16:10:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":28499229,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7236642/v1/fbe08b13-9eb9-4553-ab90-acc8b0774fb0.pdf"},{"id":88440808,"identity":"d81909cc-6514-42ca-bd3f-f2a1d36bf8e0","added_by":"auto","created_at":"2025-08-06 12:41:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":269502,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementary.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7236642/v1/f7981e40d350ac11b3c93f71.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Sample preparation induced artefacts in soft SAC solders from uncooled and cooled Argon ion milling","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMultimaterial, multicomponent packages are ubiquitous in power and microelectronics, wherein the electronic components are often joined by soldering with lowmelting, lowhardness metal alloys \u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. This complex combination of various materials in a single package poses challenges for its sample preparation for crosssectional microscopy, e.g. light optical microscopy or scanning electron microscopy (SEM) imaging. For instance, the inherently different stiffnesses of these materials may lead to damage of the sample during mechanical preparation, i.e. mechanical grinding and polishing \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Nonetheless, visualising the crosssectional microstructures of such multicomponent structures is vital for the analysis and understanding of material degradation and failure mechanisms \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan additionalcitationids=\"CR6 CR7 CR8\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. Specifically, the visualisation of microstructural changes from thermomechanical fatigue in microelectronic solder balls, which interconnect chips with the printed circuit board (PCB), is vital since degradation of these interconnects may seriously impair their integrity and the functionality of the entire electronic device \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Lowmelting Sn \u0026ndash; 3.0 wt.% Ag \u0026ndash; 0.5 wt.% Cu (SAC305) solder alloys are commonly utilised for joining in microelectronic devices due to their nontoxicity \u003csup\u003e\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e and processability \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. The intermetallic precipitates Ag\u003csub\u003e3\u003c/sub\u003eSn and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e, which form within the βSn matrix, increase the strength of the solder joint \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. In order to further lower the liquidus temperature and simultaneously increase the strength of the SAC305 alloy, Bismuth (Bi) can be additionally alloyed \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Bi acts as solidsolution strengthener in the βSn matrix, if its additions are kept below the solubility limit of ~\u0026thinsp;2.5 wt.% Bi \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Despite the various strengthening mechanisms, the βSn matrix of the solder alloy retains a relatively low hardness compared to the other materials in the multicomponent package \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. This may lead to pronounced deformation or potential crack extension in the solder ball during mechanical crosssectional sample preparation.\u003c/p\u003e\u003cp\u003eIn order to minimise mechanical deformation during sample preparation, other material removal methods, such as laser ablation and ion beam milling can be utilised. However, potential heating effects from these preparation methods may impact the sample microstructure \u003csup\u003e\u003cspan additionalcitationids=\"CR20 CR21 CR22 CR23\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. This may be a particular issue for lowmelting metals such as SAC305 alloys \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. For laser ablation methods, heating effects may be reduced by laser pulsing with ultrashort pulse durations and low laser power \u003csup\u003e\u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. By utilising laser pulse durations in the femtosecond (fs) range, the heat affected zone in metals is reportedly restricted to below 2 \u0026micro;m \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e, or more specifically, a few hundred nanometres \u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Hence, ion milling methods may be subsequently applied to remove the heat affected zone. Contrary to laser ablation, common ion beam milling methods, including broad Argon (Ar) ion milling and focussed ion beam milling, do not involve pulsing. Hence, minimising sample heating can be achieved by reducing the kinetic energy of the impinging ions, i.e. their acceleration voltage, which reduces the energy that is transmitted to the sample \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. By reducing the acceleration voltage, however, preparation time may increase significantly \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. A different approach to counter sample heating due to ion impingement involves actively cooling the sample during milling \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe aim of this work is the evaluation of artefacts that may arise during crosssectional fslaser ablation and subsequent Arion milling for fieldemission SEM (FESEM) from thermomechanically fatigued lowmelting SAC305\u0026thinsp;+\u0026thinsp;1.1 wt.% Bi solder balls, which interconnect chips with PCBs. The crosssectional preparation of these solder balls is performed with fslaser prepreparation and final crosssectional Arion milling, utilising either cooled or uncooled ion milling masks. The application of an uncooled milling mask results in submicron Curich artefacts on the solder crosssection after Arion milling is performed. Moreover, pronounced surface roughness and curtaining around precipitates are observed. However, we illustrate, that these artefacts are effectively removed when the sample is milled with a cooled ion milling mask and otherwise identical milling parameters. Despite these microstructural artefacts on the sample crosssection, no significant precipitate coarsening from uncooled Arion milling is observed. Yet, the work also illustrates that inherent thermal expansion misfits during cooling and reheating may cause strain on the multimaterial sample. Thus, it is concluded that Arion milling temperature should be chosen based on the features that are investigated. Hence, we argue that actively cooled Arion milling seems to be more suitable for studies of smallscale microstructural features, whereas uncooled milling may be preferential for analyses of fatigue cracks and mechanical strain.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cb\u003eCrosssectional sample preparation of lowhardness, lowmelting solder alloys in multicomponent microelectronic packages.\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe multimaterial, multicomponent structure of a representative microelectronic device, which is connected to the PCB by a complex arrangement of solder balls, is visualised in \u003cb\u003eFig.\u0026nbsp;1a\u003c/b\u003e via 3D Xray tomography. Due to the inherent difference in Xray attenuation by different materials, the individual electronic building blocks can be distinguished by their greyvalues and visualised accordingly. Therein, the polymer packaging of the chip is depicted in grey, chipmetallisations in blue, solder balls in silver, PCBmetallisations in orange, and the solder mask of the PCB in green. In order to prepare deformationfree sample crosssections from thermomechanically fatigued SAC305\u0026thinsp;+\u0026thinsp;1.1 wt.% Bi solder balls, neither mechanical sawing, grinding nor polishing is performed. Hence, all material removal is achieved by fslaser ablation and subsequent Arion milling. Specifically, prepreparation of the crosssections is achieved by bulk material removal utilising fslaser ablation, as schematically shown in \u003cb\u003eFig.\u0026nbsp;1b\u003c/b\u003e for one exemplary solder ball. The laser incidence is indicated in green and glass fibre reinforcements in the PCB are drawn as black lines. The prepreparation utilising a fslaser allows the fast removal of relatively large volumes, compared to ion milling methods. In order to achieve highquality crosssections for FESEM imaging, the final sample preparation is performed with broad Arion milling, schematically shown in \u003cb\u003eFig.\u0026nbsp;1c\u003c/b\u003e, wherein the direction of Arion impingement is indicated by pink arrows. During Arion milling, a metal mask, illustrated in black, is placed on top of the sample in order to define the location where the crosssection is milled and shield the rest of the sample from the impinging ion beam. Details about sample fabrication, thermomechanical fatigue, fslaser ablation and Arion milling are given in \u003cb\u003eMethods\u003c/b\u003e.\u003c/p\u003e\u003cp\u003eThe complexity of the multimaterial, multicomponent package is further illustrated in \u003cb\u003eFig.\u0026nbsp;1d\u003c/b\u003e, which shows a FESEM backscatter electron (BSE) overview micrograph of its prepared crosssection. Again, the variety of materials in the micrograph can be discerned by their greyvalues due to masscontrast. The fslaser preprepared crosssection is marked by dashed green lines, whereas the final, Arion milled crosssection is not. Additional information regarding Xray tomography and FESEM imaging are provided in \u003cb\u003eMethods\u003c/b\u003e.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMicrostructural artefacts on a solder ball crosssection prepared without actively cooling the Ar-ion milling mask.\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe final crosssectional sample preparation for FESEM imaging is performed utilising Arion milling, the milling parameters for which are given in \u003cb\u003eMethods\u003c/b\u003e. Figure\u0026nbsp;2 shows micrographs of a representative solder ball after sample preparation without active cooling of the ion milling mask. FESEMBSE and secondary electron (SE) micrographs with increasing magnifications are shown in \u003cb\u003eFig.\u0026nbsp;2a\u003c/b\u003e and \u003cb\u003eb\u003c/b\u003e, respectively. Figure\u0026nbsp;2\u003cb\u003ec\u003c/b\u003e and \u003cb\u003ed\u003c/b\u003e illustrate the energy dispersive Xray spectroscopy (EDX) mapping of the largest magnification, ROI 2, for Cu and Ag, respectively. EDX signals of Sn and Bi are provided in \u003cb\u003eSupplementary Fig.\u0026nbsp;1\u003c/b\u003e. Crystallographic information about ROI 2 is provided in \u003cb\u003eFig.\u0026nbsp;2e\u003c/b\u003e, wherein its electron backscatter diffraction (EBSD) phase mapping is shown. Therein, βSn is shown in blue, Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e in yellow and Ag\u003csub\u003e3\u003c/sub\u003eSn in red. EBSD inverse pole figure (IPF) and phase mappings of the entire solder ball are provided in \u003cb\u003eSupplementary Fig.\u0026nbsp;2\u003c/b\u003e. Details about FESEM imaging, as well as EDX and EBSD mapping are provided in \u003cb\u003eMethods\u003c/b\u003e.\u003c/p\u003e\u003cp\u003e\u003cb\u003eFigure 2\u003c/b\u003e shows that, in addition to larger Ag\u003csub\u003e3\u003c/sub\u003eSn and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003eprecipitates, fine, Curich lines are present on the crosssection. These lines are especially apparent in the BSE micrographs of ROI 1 and 2 in \u003cb\u003eFig.\u0026nbsp;1a\u003c/b\u003e and the EDX mapping of ROI 2 in \u003cb\u003eFig.\u0026nbsp;1c\u003c/b\u003e. An additional crosssection prepared with the same ion milling parameters is shown in \u003cb\u003eSupplementary Fig.\u0026nbsp;3\u003c/b\u003e. Those FESEMBSE micrographs in \u003cb\u003eSupplementary Fig.\u0026nbsp;3a\u003c/b\u003e exhibit similar lines within the βSn grains, as well as thicker ones along the grain boundaries in ROI B. Given the needle shape of the Curich agglomerations, dotted areas on the FESEM crosssections would suggest Cuneedle growth away from the crosssection, i.e. into the solder ball bulk. In order to investigate, whether these needles are also present in the bulk material, a lamella liftout for scanning transmission electron microscopy (STEM) is performed in such a Curich dotted region, see \u003cb\u003eSupplementary Fig.\u0026nbsp;4\u003c/b\u003e. However, the corresponding STEM bright field (BF) micrographs and STEMEDX mappings in \u003cb\u003eSupplementary Fig.\u0026nbsp;4b\u003c/b\u003e only exhibit two Curich dots at the crosssection surface, while the rest of the lamella is homogeneous. This finding shows that the Curich agglomerations only form on the surface of the Arion milled crosssection, suggesting that they are artefacts from the preparation. Moreover, the SE micrographs in \u003cb\u003eFig.\u0026nbsp;1b\u003c/b\u003e and \u003cb\u003eSupplementary Fig.\u0026nbsp;3b\u003c/b\u003e visualise a pronounced, periodic surface roughness. \u003cb\u003eSupplementary Fig.\u0026nbsp;3b\u003c/b\u003e also shows pronounced curtaining originating from Ag\u003csub\u003e3\u003c/sub\u003eSnprecipitates.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMicrostructure of a crosssection prepared utilising an actively cooled Ar-ion milling mask.\u003c/b\u003e\u003c/p\u003e\u003cp\u003eIn the following, we investigate whether and how the microstructure of the lowmelting SAC305\u0026thinsp;+\u0026thinsp;1.1 wt.% Bi solder alloy is affected by Arion milling with an actively cooled milling mask. We utilise the same Arion milling parameters as for the previous milling with the uncooled milling mask, only that the milling mask is actively cooled to -100\u0026deg;C. Details are given in \u003cb\u003eMethods\u003c/b\u003e. Figure\u0026nbsp;3 depicts FESEM micrographs of a representative solder ball that is prepared with an actively cooled ion milling mask. Micrographs of an additional solder ball prepared in the same way are shown in \u003cb\u003eSupplementary Fig.\u0026nbsp;7\u003c/b\u003e. Figures\u0026nbsp;3\u003cb\u003ea\u003c/b\u003e and \u003cb\u003eb\u003c/b\u003e show increasing magnifications of FESEMBSE and SE micrographs, respectively. The largest magnification, ROI 4, is mapped utilising EDX. The respective Cu and AgEDX mappings are shown in \u003cb\u003eFig.\u0026nbsp;3c\u003c/b\u003e and \u003cb\u003ed\u003c/b\u003e, Sn and BiEDX mappings in \u003cb\u003eSupplementary Fig.\u0026nbsp;5\u003c/b\u003e. Moreover, the EBSDphase mapping of ROI 4 is shown in \u003cb\u003eFig.\u0026nbsp;3e\u003c/b\u003e, wherein βSn is coloured blue, Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e yellow and Ag\u003csub\u003e3\u003c/sub\u003eSn red. EBSDIPF and phase mappings of the entire solder ball are depicted in \u003cb\u003eSupplementary Fig.\u0026nbsp;6\u003c/b\u003e.\u003c/p\u003e\u003cp\u003eContrary to the micrographs from uncooled preparation in \u003cb\u003eFig.\u0026nbsp;2\u003c/b\u003e, \u003cb\u003eFig.\u0026nbsp;3\u003c/b\u003e and \u003cb\u003eSupplementary Fig.\u0026nbsp;6\u003c/b\u003e show that no Curich lines are visible in the micrographs after actively cooled Arion milling. Furthermore, both surface roughness and curtaining around precipitates are reduced significantly, which is evident from the SEmicrographs in \u003cb\u003eFig.\u0026nbsp;3b\u003c/b\u003e and \u003cb\u003eSupplementary Fig.\u0026nbsp;7b\u003c/b\u003e.\u003c/p\u003e\u003cp\u003e\u003cb\u003eInsitu temperature measurement during Arion milling without active cooling.\u003c/b\u003e\u003c/p\u003e\u003cp\u003eIn order to quantitatively evaluate the temperaturerise during Arion milling, an insitu temperature measurement setup is built, schematically shown in \u003cb\u003eFig.\u0026nbsp;4a\u003c/b\u003e. A vacuum flange with a thermocouple feedthrough is machined and mounted onto the ion milling system, connecting the sample inside the vacuum chamber with a multimeter on the outside. From the multimeter, the temperature of the thermocouple inside the vacuum chamber can be read. Figure\u0026nbsp;4\u003cb\u003eb\u003c/b\u003e depicts the fixture of the thermocouple on the sample. One row of solder balls is separated from the microelectronic package utilising fslaser ablation and placed on a Siwafer piece, in order to ensure the thermocouple can be placed as close to the Arion milling area as possible. Thus, the thermocouple is placed between the ion milling mask and the sample on the Siwafer piece, and fixed utilising conductive silver paste. Hence, it provides temperature readings directly from the Arion milling area. Arion milling is performed with the same acceleration voltage as the previous millings, but the sample stage is not swung, as not to break the fixture of the thermocouple. Figure\u0026nbsp;4\u003cb\u003ec\u003c/b\u003e shows the temperature profile that is measured during Arion milling utilising these parameters. The temperature increases rapidly to 40\u0026deg;C at the beginning of milling and saturates at 50\u0026deg;C after ~\u0026thinsp;2 hours. A light optical image of the crosssection after milling is depicted in \u003cb\u003eFig.\u0026nbsp;4d\u003c/b\u003e. The chip and PCBmetallisations are discernible due to their Cucolouration.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMicrostructural Differences: Scrutinising potential precipitate coarsening and thermal expansion anisotropy.\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFurther, due to the temperature rise during uncooled Arion milling and due to the microstructural differences between crosssections prepared with and without active cooling, potential precipitate coarsening during the sample preparation without active cooling is studied. To that end, Ag and CuEDX mappings of ROI 2 and ROI 4 are comparatively analysed and mean equivalent precipitate radii are calculated, the results of which are shown in \u003cb\u003eFig.\u0026nbsp;5\u003c/b\u003e. The contours of the precipitates which are included in the analysis are drawn in yellow and the mean equivalent radii, as well as standard deviations, are printed on the top of each contour image. For the analysis of the CuEDX mapping of ROI 2, the lineshaped enrichments are excluded from the evaluation. Details about image processing and radii calculations are provided in \u003cb\u003eMethods\u003c/b\u003e. The quantitative precipitate size analyses in \u003cb\u003eFig.\u0026nbsp;5\u003c/b\u003e reveal no precipitate coarsening in ROI 2 from uncooled crosssectional Arion milling compared to ROI 4, since the mean equivalent precipitate radii of both Ag\u003csub\u003e3\u003c/sub\u003eSn and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e lie within the standard deviations of the respectively other preparation method.\u003c/p\u003e\u003cp\u003eAlthough actively cooled Arion milling produces Cu artefactfree SAC crosssections with reduced curtaining and surface roughness, issues arise in some parts of the crosssection when the sample is reheated to room temperature after milling. Figure\u0026nbsp;6 depicts FESEM micrographs of the solder ball from \u003cb\u003eFig.\u0026nbsp;3\u003c/b\u003e, which is milled utilising an actively cooled milling mask. Displacements along grain boundaries are discernible in the FESEMSE micrograph in \u003cb\u003eFig.\u0026nbsp;6a\u003c/b\u003e and especially in the detail of ROI 5 shown in \u003cb\u003eFig.\u0026nbsp;6b\u003c/b\u003e. The EBSDIPF mapping in \u003cb\u003eFig.\u0026nbsp;6c\u003c/b\u003e confirms that the displacement of recrystallised βSn grains occurs along grain boundaries. These displacements may arise after cooled Arion milling at -100\u0026deg;C, when the sample is reheated. Therein, previously recrystallised grains may expand to different extents due to the large thermal expansion anisotropy of βSn \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e, leading to discontinuities on the Arion polished free surface.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eReliable, artefactfree sample preparation for microstructural imaging is crucial for the indepth understanding of material properties and behaviour. However, crosssectional sample preparation of multicomponent, multimaterial stacks, such as microelectronic packages, poses challenges due to the inherent differences in stiffness, hardness and sputter yield of the various materials. Therein, particular care needs to be taken for the crosssectional preparation of lowhardness, lowmelting SACsolder balls \u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e–\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, which are sandwiched between the chip and the PCB in microelectronic boardlevel packages. Hence, these solder balls are not directly accessible for crosssectional imaging methods and multiple additional components of the package need to be considered during the preparation of crosssections. Because of the comparably low hardness of the βSn matrix \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, crosssectional mechanical grinding and polishing of the device may lead to deformation of the SACsolder balls. Moreover, thermomechanically cycled solder balls may exhibit fatigue cracks \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan additionalcitationids=\"CR6 CR7 CR8\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e–\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan additionalcitationids=\"CR37\" citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e–\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e, which could be extended during mechanical preparation.\u003c/p\u003e\u003cp\u003eTherefore, this study seeks to optimise the crosssectional sample preparation of such multicomponent devices, which include lowmelting components, for SEM imaging utilising fslayer ablation and Arion milling. H4erein, fslaser ablation is utilised for the removal of large sample volumes and the final sample crosssection is polished utilising Arion milling. Since Arion milling is the last preparation step, potential heating effects in the process may affect the microstructure of the lowmelting SACsolder joint that interconnects the microelectronic components. Such artefacts are shown in \u003cb\u003eFig.\u0026nbsp;2a\u003c/b\u003e and \u003cb\u003ec\u003c/b\u003e, \u003cb\u003eSupplementary Fig.\u0026nbsp;1\u003c/b\u003e and \u003cb\u003eSupplementary Fig.\u0026nbsp;3\u003c/b\u003e. Fine Curich structures form on the SAC crosssection during uncooled Arion milling. However, these structures only form on the surface of the Arion milled crosssection, as shown with STEMEDX in \u003cb\u003eSupplementary Fig.\u0026nbsp;4.\u003c/b\u003e Moreover, these Curich structures are not present on crosssections that are prepared with a cryogenically cooled ion milling mask, as depicted in \u003cb\u003eFig.\u0026nbsp;3a\u003c/b\u003e and \u003cb\u003ec\u003c/b\u003e, \u003cb\u003eSupplementary Fig.\u0026nbsp;5\u003c/b\u003e and \u003cb\u003eSupplementary Fig.\u0026nbsp;7\u003c/b\u003e, which indicates a temperaturedependency of the formation of these Curich structures. Insitu temperature measurement, shown in \u003cb\u003eFig.\u0026nbsp;4\u003c/b\u003e, reveals a temperatureincrease up to 50°C during uncooled Arion milling. However, this temperatureincrease during Arion milling does not cause precipitate coarsening of neither Ag\u003csub\u003e3\u003c/sub\u003eSn nor Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e, as \u003cb\u003eFig.\u0026nbsp;5\u003c/b\u003e illustrates. Hence, the Arion induced heating may not suffice for precipitate coarsening, but the results suggest that the temperatureincrease on the SAC surface plays a crucial role for artefactfree crosssectional preparation. \u003cb\u003eSupplementary Fig.\u0026nbsp;8a\u003c/b\u003e and \u003cb\u003eb\u003c/b\u003e show laser confocal surface profiles in the directions of Arion milling utilising uncooled and cooled milling masks. These crosssections correspond to those depicted in \u003cb\u003eFig.\u0026nbsp;2\u003c/b\u003e and \u003cb\u003eFig.\u0026nbsp;3\u003c/b\u003e, respectively. Both surface profiles reveal that the SACsolder ball surface is intruded, compared to the Cu metallisations on both chipand PCBside, indicating that the SACsolder ball is milled preferentially. Similar observations of preferential ion milling of SACalloys are made in \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eConsidering that the multimaterial stack is milled from chip to PCB, as sketched in \u003cb\u003eFig.\u0026nbsp;1b\u003c/b\u003e, the SACsolder ball is already milled when the Arion beam reaches the PCBCu metallisation. Hence, Cu that is subsequently milled from the PCBmetallisation is redeposited onto the solder ball\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e and cannot be removed thereafter, since the SAC crosssection is intruded with respect to the chip and the ion milling mask. However, the absence of the Curich structures on the crosssections that are actively cooled during Arion milling, see \u003cb\u003eFig.\u0026nbsp;3\u003c/b\u003e and \u003cb\u003eSupplementary Fig.\u0026nbsp;7\u003c/b\u003e, suggests that they only form at elevated surface temperatures, which are shown to reach up to 50°C during uncooled milling, see \u003cb\u003eFig.\u0026nbsp;4\u003c/b\u003e. Therefore, the formation of Curich structures may be suppressed at -100°C when Arion milling is performed utilising an actively cooled mask. It should be noted that thicker Curich structures in \u003cb\u003eFig.\u0026nbsp;2d\u003c/b\u003e are indexed as Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e in the EBSDphase mapping. In the field of metallic thinfilms, ion bombardment has proven to be a useful tool for the fabrication of selforganised micro and nanopatterns \u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. Moreover, monolayers and thin films have been shown to change their morphologies when the substrate temperatures are varied during deposition \u003csup\u003e\u003cspan additionalcitationids=\"CR43\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e–\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. Hence, the assembly of resputtered Cu from the PCBmetallisation into lineshaped Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e on the SACsolder crosssection may be facilitated by Arion bombardment, combined with surface migration at 50°C. The distinctly lineshaped morphology of the Curich structures and their presence along βSn grain boundaries in \u003cb\u003eSupplementary Fig.\u0026nbsp;3\u003c/b\u003e may indicate preferred formation of Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e in certain areas on the solder ball surface. Cu that is resputtered onto the solder ball crosssection may migrate towards areas with higher energies, where Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003eformation could be preferential. Both surface migration of Cu and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003ephase formation may be hindered at -100°C, which could explain the absence of these structures after actively cooled Arion milling.\u003c/p\u003e\u003cp\u003eIn addition to the absence of these fine Curich structures, the surface roughness of the βSn matrix decreases visibly when the ion milling mask is actively cooled, compared to the preparation with an uncooled mask. This effect is discernible when comparing \u003cb\u003eFig.\u0026nbsp;2b\u003c/b\u003e with \u003cb\u003eFig.\u0026nbsp;3b\u003c/b\u003e. The suppression of this surface artefact may stem from the suppression of surface migration of vacancies and adatoms \u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. Furthermore, curtaining artefacts around precipitates, discernible in \u003cb\u003eSupplementary Fig.\u0026nbsp;3\u003c/b\u003e, are minimised with active cooling of the ion milling mask, which may be attributed to a decrease of sputtering yield of the βSn matrix at -100°C, as observed in \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eDespite its advantages regarding the suppression of Curich artefacts and decreased surface roughness, actively cooled Arion milling poses one disadvantage. As discernible in \u003cb\u003eFig.\u0026nbsp;6\u003c/b\u003e, individual βSn grains are displaced along grain boundaries after actively cooled Arion milling. In addition, the surface profile of the crosssection in \u003cb\u003eSupplementary Fig.\u0026nbsp;8b\u003c/b\u003e, which is milled with an actively cooled mask, shows that recrystallised grains are elevated compared to the rest of the singlecrystalline solder ball. The displacement of recrystallised grains may be exacerbated by the high thermal expansion anisotropy of βSn \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e, but should be especially considered for the preparation of multicomponent, multimaterial stacks, since the inherently different thermal expansion coefficients may cause substantial misfit stresses during cooling and reheating of the sample \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan additionalcitationids=\"CR36\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e–\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eIn summary, microstructural artefacts in lowmelting SACsolder balls stemming from Arion milling of multicomponent microelectronic devices are evaluated. Both surface roughness and veridical presentation of microstructural features are improved by actively cooled Arion milling. However, misfit stresses may arise during actively cooled Arion milling due to thermal expansion misfits. Hence, special care needs to be taken for the preparation of multimaterial samples. Therefore, Arion milling temperature should be chosen based on the features that are studied. For the investigation of small microstructural features, actively cooled Arion milling may be preferential, whereas uncooled Arion milling may be more suitable the evaluation of strains and crack propagation.\u003c/p\u003e"},{"header":"Methods","content":"\u003ch3\u003e\u003cstrong\u003eSample material and geometry.\u003c/strong\u003e\u003c/h3\u003e\n\u003cp\u003eThe investigated solder balls are produced by droplet spraying in an inert N2 atmosphere and subsequently soldered between the Cu‑metallisations of the chip and the PCB. Reflow is done at a peak temperature of 240\u0026nbsp;\u0026deg;C and with a mean heating rate of 44\u0026nbsp;\u0026deg;C/min in inert N2 atmosphere, followed by rapid air cooling to 90\u0026nbsp;\u0026deg;C with a mean cooling rate of 107\u0026nbsp;\u0026deg;C/min and ambient air cooling to room temperature. The investigated SAC305\u0026nbsp;+\u0026nbsp;1.1\u0026nbsp;wt.%\u0026nbsp;Bi sample is thermally cycled 2914 times between -40 \u0026ndash; 125\u0026nbsp;\u0026deg;C with ramp‑ and dwell‑times of 15\u0026nbsp;mins, respectively.\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003e3D X\u0026nbsp;ray tomography.\u003c/strong\u003e\u003c/h3\u003e\n\u003cp\u003eA 3D\u0026nbsp;X\u0026nbsp;ray tomography scan of a representative BGA is done utilising a GE Phoenix Nanotom\u0026nbsp;M\u0026nbsp;(research edition) with 110\u0026nbsp;kV acceleration voltage, 120\u0026nbsp;\u0026micro;A tube current and a cone‑beam. By utilising a cone‑beam, the achievable spatial resolution is dependent on the lateral sample size\u0026nbsp;(~\u0026nbsp;10\u0026nbsp;x\u0026nbsp;7\u0026nbsp;mm\u003csup\u003e2\u003c/sup\u003e). For the investigated sample, this results in a voxel size of 5.33\u0026nbsp;x\u0026nbsp;5.33\u0026nbsp;x\u0026nbsp;5.33\u0026nbsp;\u0026micro;m\u003csup\u003e3\u003c/sup\u003e. The different building blocks of the device, i.e. the chip, solder balls and the PCB are distinguishable due to their various grey‑values and reconstructed utilising VGSTUDIO MAX.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003eSample preparation.\u003c/strong\u003e\u003c/h3\u003e\n\u003cp\u003eA 3D Micromac microPREP PRO FEMTO fs‑laser with a laser power of 300 mW is used to pre‑prepare the cross‑sections for FESEM. This laser has a wavelength of 515 nm and a pulse length of less than 300 fs. The final cross‑sections for FESEM imaging are prepared utilising Ar‑ion milling. Uncooled Ar‑ion milling is done with a Hitachi IM4000+ ion milling system. The accelerating voltage for ion slicing is set to 6 kV and the swing angle to 30\u0026deg;\u0026nbsp;with 3 swings per\u0026nbsp;minute. Ar‑ion milling with the actively cooled mask is done with a Hitachi IM5000+ ion milling system, utilising the same milling parameters and cooling the ion milling mask to ‑100 \u0026deg;C.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003eFESEM imaging.\u003c/strong\u003e\u003c/h3\u003e\n\u003cp\u003eThe FESEM‑BSE and ‑SE micrographs are acquired with a\u0026nbsp;Zeiss Crossbeam 550 FESEM utilising an acceleration voltage of 3\u0026nbsp;kV and sample currents of 3\u0026nbsp;nA. The EDX\u0026nbsp;mappings are done utilising an Oxford Ultim Extreme detector. The EBSD\u0026nbsp;maps are acquired with an accelerating voltage of 20\u0026nbsp;kV, a step size of 400\u0026nbsp;nm and an Oxford Symmetry\u0026nbsp;S3 detector. Oxford Instruments AZtec\u0026nbsp;6.2. is utilised for the EDX and EBSD analyses.\u003c/p\u003e\n\u003ch3\u003e\u003cstrong\u003ePrecipitate size analysis.\u003c/strong\u003e\u003c/h3\u003e\n\u003cp\u003eIn order to determine, whether the heating from Ar‑ion milling causes precipitate coarsening when the milling mask is not actively cooled, the Ag\u003csub\u003e3\u003c/sub\u003eSn‑ and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e‑precipitate sizes are evaluated and compared to those after utilising a cooled mask. The calculations of the mean equivalent Ag\u003csub\u003e3\u003c/sub\u003eSn‑ and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e‑precipitate radii in \u003cstrong\u003eFig.\u0026nbsp;5\u003c/strong\u003e are done based on the Ag‑ and Cu‑EDX mappings of ROI 2 and ROI 4, shown in \u003cstrong\u003eSupplementary\u0026nbsp;Fig.\u0026nbsp;2\u003c/strong\u003e and \u003cstrong\u003e6\u003c/strong\u003e, respectively. To that end, the respective EDX mappings are binarily thresholded and the contours are detected. In order to exclude the Cu‑rich, line‑shaped artefacts in ROI 2 from the analysis, limits are set for the areas and aspect‑ratios of the detected contours. Finally, the contour areas are evaluated and their equivalent radii are calculated. The results of these analyses are shown in \u003cstrong\u003eFig.\u0026nbsp;4\u003c/strong\u003e. The analysis is done with Python 3.8.13, OpenCV 4.0.1 and numpy 1.22.3. For the visualisation, matplotlib 3.5.1 is utilised.\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrespondence\u003c/strong\u003eand requests for materials should be addressed to R.B.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll code that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eC.C. did the image-analysis work, data interpretation and evaluation under the supervision of R.B.; C.C. and B.S. performed the in‑situ temperature measurement in discussion with R.B.; W.H. fabricated and provided the samples, with support from M.R. and P.I; C.C., B.S. and R.B. planned the FESEM‑BSE, EDX and EBSD; C.C. and R.B. wrote the paper; All authors discussed the results and commented on the paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe acknowledge the support from J.\u0026nbsp;Rosc for the X\u0026nbsp;ray tomography scan, K.\u0026nbsp;Fischak for the SEM, EDX and EBSD measurements, L.\u0026nbsp;Schieder for the actively cooled Ar‑ion milling, M.\u0026nbsp;Burtscher and D.\u0026nbsp;Kiener for the STEM‑BF and STEM‑EDX measurements and M.\u0026nbsp;Tkadletz for the laser confocal profiling.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the financial support under the scope of the COMET program within the K2 Center “Integrated Computational Material, Process and Product Engineering (IC-MPPE)” (Project No 886385). This program is supported by the Austrian Federal Ministries for Climate Action, Environment, Energy, Mobility, Innovation and Technology (BMK) and for Labour and Economy (BMAW), represented by the Austrian Research Promotion Agency (FFG), and the federal states of Styria, Upper Austria and Tyrol, P. No. P2.22 ECOSolder.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBen Romdhane, E., Gu\u0026eacute;don-Gracia, A., Pin, S., Roumanille, P. \u0026amp; Fr\u0026eacute;mont, H. Impact of crystalline orientation of lead-free solder joints on thermomechanical response and reliability of ball grid array components. \u003cem\u003eMicroelectronics Reliability \u003c/em\u003e114, 113812 (2020).\u003c/li\u003e\n\u003cli\u003eDeshpande, A., Kaeser, H. \u0026amp; Dasgupta, A. Effect of Stress State on Fatigue Characterization of SAC305 Solder Joints. 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Tin pest in Sn-0.5 wt.% Cu lead-free solder. \u003cem\u003eJOM \u003c/em\u003e53, 39\u0026ndash;41 (2001).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7236642/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7236642/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eComplex combinations of various materials in microelectronic packages pose challenges for sample preparation. Reliable cross-sectional sample preparation is critical for microstructural analysis, especially when utilising low-melting Sn‑Ag‑Cu (SAC) solders, which are easily deformed or damaged by mechanical grinding. Hence, this study explores the impact of femtosecond laser ablation for bulk material removal and subsequent Ar‑ion milling for final cross‑sectional polishing, comparing cooled and uncooled milling masks. We reveal that uncooled Ar-ion milling causes artefacts like increased surface roughness and fine Cu‑rich structures due to surface heating (~50 °C) combined with Cu redeposition on the preferentially milled, intruded SAC‑surface. Cryogenic cooling of the milling mask to -100 °C reduces these effects, minimising curtaining and preserving detail. However, cooled milling results in the displacement of recrystallised grains at grain boundaries due to the thermal expansion anisotropy of β-Sn. Thus, milling parameters must be carefully tailored to the desired preservation of microstructure, cracks and strain.\u003c/p\u003e","manuscriptTitle":"Sample preparation induced artefacts in soft SAC solders from uncooled and cooled Argon ion milling","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-06 12:25:31","doi":"10.21203/rs.3.rs-7236642/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-09-04T10:54:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-03T10:41:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-30T13:00:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"320212092493778181761540257751046548292","date":"2025-08-26T04:07:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"333245063106392359668253001974218353116","date":"2025-08-25T13:18:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"264262535625158199524211316343391517896","date":"2025-08-09T19:15:24+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-04T17:46:21+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-08-04T16:26:29+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-31T06:27:54+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-30T13:54:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-07-28T18:33:42+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"dac6f251-d68c-4c0f-adc8-72f28dc4a0a6","owner":[],"postedDate":"August 6th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":52671853,"name":"Physical sciences/Engineering"},{"id":52671854,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2025-11-24T16:05:25+00:00","versionOfRecord":{"articleIdentity":"rs-7236642","link":"https://doi.org/10.1038/s41598-025-25169-z","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-11-21 15:57:08","publishedOnDateReadable":"November 21st, 2025"},"versionCreatedAt":"2025-08-06 12:25:31","video":"","vorDoi":"10.1038/s41598-025-25169-z","vorDoiUrl":"https://doi.org/10.1038/s41598-025-25169-z","workflowStages":[]},"version":"v1","identity":"rs-7236642","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7236642","identity":"rs-7236642","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}