Improving the thermo-mechanical reliability of solderable isotropic conductive adhesive joints by using low- and high-melting-point solder fillers

Improving the thermo-mechanical reliability of solderable isotropic conductive adhesive joints by using low- and high-melting-point solder fillers | 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 Research Article Improving the thermo-mechanical reliability of solderable isotropic conductive adhesive joints by using low- and high-melting-point solder fillers Yi Hyeon Baek, Myeong Jin Jung, Jeong Il Lee, Jong-Min Kim, Byung-Seung Yim This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7872022/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 21 Dec, 2025 Read the published version in Journal of Materials Science: Materials in Electronics → Version 1 posted You are reading this latest preprint version Abstract In this study, we investigated the effect of adding a mixed low-melting-point solder (LMS)/high-melting-point-solder (HMS) filler on the thermo-mechanical reliability of solderable isotropic conductive adhesive (SICA) joints. To this end, we compared the properties and thermo-mechanical reliability of L-SICA (fabricated with LMS filler) and LH-SICA (fabricated with the mixed LMS/HMS filler). LH-SICA exhibited enhanced mechanical interconnection properties compared with L-SICA due to precipitation hardening and dispersion strengthening effects arising from the distribution of intermetallic compounds (IMCs) Ag 3 Sn and Cu 6 Sn 5 , and Bi-rich phase particles within the joint. The results of thermal shock testing revealed that the electrical reliability of both SICA assemblies remained stable owing to the formation of a metallurgical conduction path between the corresponding leads and electrodes through the molten solder filler. Although the pull strength of SICA assemblies tended to decrease compared with their initial pull strength during thermal shock testing, LH-SICA exhibited improved thermo-mechanical reliability compared with L-SICA. This is due to the enhanced bonding properties, a reduction in microstructural coarsening, slower growth and flattening of the IMC layer at the bonding interface, and a reduction in the accumulated Bi-rich phase at the bulk solder/Cu 6 Sn 5 IMC interface resulting from changes in the composition of the LH-SICA joint. high melting point solder low melting point solder polymer composites reliability solderable isotropic conductive adhesive Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1 Introduction High functionalization, high integration, and miniaturization of electronic packages have been accelerated in the electronic package industry [ 1 ]. When electronic packages comprising various materials with different coefficients of thermal expansion (CTEs) are exposed to harsh environments (e.g., thermal shock or repetitive thermal fluctuations induced by power consumption or external environmental changes), CTE mismatches between package materials induce high interfacial stresses, which can lead to crack initiation and propagation. Ultimately, this causes the entire electronic package to lose its functionality via interface delamination and fracturing [ 2 – 4 ]. Therefore, overcoming this thermo-mechanical reliability issue is critical importance in the electronic package industry [ 5 ]. Among the interconnection materials for electronic packages, conventional electrically conductive adhesives (ECAs) containing polymer resin and non-fusible metal fillers have been extensively studied as an alternative to lead-free solder because of advantages such as low-temperature processing, process simplification, fine-pitch capability, eco-friendliness, and compatibility with various materials [ 6 , 7 ]. However, despite these advantages, the use of conventional ECAs is limited because of issues such as low electrical stability, thermal durability, and low shock and joint strength due to their conduction mechanism: electrically interconnecting the two electrodes through the physical contact of non-fusible fillers [ 8 , 9 ]. Moreover, contact between the metal filler and electrodes can be lost due to moisture absorption by the polymer, weakened adhesion in a high-temperature/high-humidity environment, and/or repeated thermal shock, thus making it difficult to ensure the reliability of the ECA joint [ 10 , 11 ]. To overcome these problems, research has been conducted on solderable isotropic conductive adhesives (SICAs) composed of a polymer with fluxing capability and a fusible low-melting-point solder (LMS) filler [ 12 – 14 ]. SICAs solve the problems of conventional ECAs by forming a metallurgical conduction path between the leads and electrodes through internal flow and coalescence of the molten LMS, as well as wetting behavior of the coalesced LMS on the electrodes within the polymer during the reflow process. Moreover, this provides better mechanical interconnection properties than those of commercial solder joints due to the reinforcing effect of the cured polymer surrounding the conduction path. To form a suitably wide and stable conduction path with in the SICA interconnection process, it is essential to use an LMS filler with a lower melting point than the curing temperature of the thermosetting polymer. To this end, Sn–58Bi eutectic solder with a melting point of 139 ℃ is commonly used as an LMS filler in the synthesis of typical SICAs. However, the resulting solder joint has problems with interconnection properties and reliability due to several issues, such as low ductility caused by the brittle nature of Bi, coarsening of the Bi-phase within the bulk solder, rapid growth of the intermetallic compound (IMC) in the bonding interface, and accompanying segregation of the Bi-phase [ 2 , 15 – 17 ]. To overcome these problems, we previously fabricated and investigated a mixed LMS/high-melting-point-solder (HMS) filler filled SICA (LH-SICA) [ 18 – 20 ]. Figure 1 shows the conduction path formation mechanism in LH-SICA. During the reflow process, the molten LMS filler disperses within the polymer by flowing and coalescing inside the low-viscosity polymer while the solid-state HMS filler is simultaneously absorbed through contact with the molten LMS filler. Meanwhile, the wetting behavior of the combination forms a metallurgical conduction path between the leads and electrodes. When the temperature reaches the melting point of the HMS fillers, it melts and forms a solid solution with the molten LMS filler, with bonding completed by fully curing polymer. Our investigation confirmed that the joint formed with LH-SICA achieved better mechanical interconnection properties than that of a SICA containing an LMS filler only (L-SICA) due to the reinforcing effect (including precipitation hardening and dispersion strengthening effects) by fine IMCs (i.e., Cu 6 Sn 5 and Ag 3 Sn) and Bi-rich phase particles dispersed within the conduction path. In the present work, we fabricated thin quad flat package (TQFP) assemblies containing L-SICA (with LMS filler) and LH-SICA (with mixed LMS/HMS filler. Afterward, we investigated the thermo-mechanical reliability of SICA joints using these materials via thermal shock testing, during which we evaluated the electrical and mechanical performances of both SICA assemblies. Figure 1 2 Experimental 2.1 Materials The SICA assemblies used in this study contained a polymer composite functionalized with fluxing capability and a fusible solder filler for the formation of metallurgical conduction paths and electrical connections. In the formulation of the polymer composite, thermosetting epoxy diglycidyl ether of bisphenol A (DGEBA), 4,4'-diaminodiphenylmethane (DDM), and boron trifluoro-mono-ethylamine (BF 3 MEA) were used as the base resin, curing agent, and catalyst, respectively (Table 1 ). Carboxylic acid was used as a fluxing agent to remove the oxide layer on the electrodes and metal fillers during the reflow process. Sn–58Bi (with a melting point of 139 ℃) and Sn–3.0Ag–0.5Cu (with a melting point of 219 ℃) were used as the LMS and HMS fillers, respectively. Both had a mean particle diameter of 38 µm. Table 1 Components of the proposed LH-SICAs Components L-SICA LH-SICA Polymer composite Base resin DGEBA Curing agent DDM Catalyst BF3MEA Reductant Carboxylic acid Fusible filler LMS Sn-58Bi (φ 38 µm) HMS Sn–3Ag–0.5Cu (φ: 38 µm) LMS/HMS mixing ratio (vol%) 100:0 50:50 For the reliability testing, TQFP (TQFP44T30, Topline Co., USA) assemblies (12 × 12 × 1.2 mm 3 ) were prepared with 44 Sn-plated leads (11 attached to each side of the TQFP body) with a lead pitch of 0.8 mm. Printed circuit boards (PCBs) (32 × 32 × 1.0 mm 3 ) were equipped with bare Cu electrodes (without surface finish) plated to a thickness of 18 µm. Daisy chains of solder joints were formed on the TQFPs and PCBs to measure the electrical reliability of the SICA assemblies during the reliability testing. Table 1 2.2 Test method 2.2.1 Preparation of test assessment To evaluate the influence of the mixed LMS/HMS filler on thermo-mechanical reliability of SICA, L-SICA containing only LMS filler, and LH-SICA containing a mixed LMS/HMS filler (volume fraction (vol%) between LMS and HMS: 50:50) were synthesized. The total solder filler content within the SICA assemblies was set to 30 vol% to form a wide and stable conduction path between the leads and electrodes. To create TQFP interconnections using the SICA assemblies, a metal mask (100 µm in thickness) was aligned and mounted on the cleaned PCB, and a uniform amount of SICA was applied to the exposed electrodes using the squeegee method. After completing SICA application, the TQFP leads were aligned and mounted onto the corresponding electrodes using a flip-chip bonding machine (LAMBDA, Finetech Co., Germany), and the reflow process was carried out according to the reflow profiles shown in Fig. 2 . The L-SICA specimens were reflowed from room temperature to 180 ℃ at a heating rate of 120 ℃ min − 1 , and held at the peak temperature for approximately 2 min to cure the polymer composite. The LH-SICA specimens were heated from room temperature to 240 ℃ at the same heating rate to melt the HMS filler, and held at the peak temperature for approximately 2 min. Afterward, to confirm the morphology of the conduction paths created therein, the specimens were cross-sectioned and then observed under an optical microscope (VHX-1000, Keyence Co., Japan). Figure 2 2.2.2 Reliability testing To investigate the influence of the mixed LMS/HMS filler on the thermo-mechanical reliability of SICA joints in harsh environments, thermal shock testing was conducted in a thermal shock chamber (TSE-11-A, Espec Corp., Japan). In accordance with JEDEC standard JESD22-A106B C, both SICA assemblies were exposed to repetitive thermal fluctuations from − 55 ℃ to 125 ℃ 1000 cycles. Each cycle lasted 30 minutes (with a dwell time of 15 minutes at each peak temperature); the transfer time between peak temperatures was 10 s, and the heating and cooling rates were both approximately 18°C s − 1 . To measure any changes in electrical performance during the thermal shock test, the electrical resistance of the SICA joints was measured using a multimeter (34410A, Agilent Tech., USA). Subsequently, changes in the mechanical properties of the SICA joints during the thermal shock test were determined via 45° pull testing on the TQFP leads using a pull tester (PTR-1000, Rhesca Co., Japan). In accordance with JEDEC standard JIS Z 3198-6, the TQFP specimens were clamped in the pull tester apparatus at 45°, and then the TQFP leads were pulled upward at a pull rate of 6 mm min − 1 . 2.2.3 Microstructure analysis To investigate any microstructural changes and interfacial IMC layer growth between the conduction path and electrodes in the SICA joints, they were examined after specific numbers of thermal shock cycles (i.e., 0, 200, 500, and 1000 cycles) during the thermal shock testing. Beforehand, the SICA specimens were cross-sectioned by grinding using silicon carbide paper and subsequently polished with a 3 µm diamond suspension. The cross-sectioned surfaces were then etched for 10 s using an etching solution of 90% methanol and 10% nitric acid to clearly reveal the phase boundaries of the IMC and the microstructure of the SICA joints. The specimens were then examined using field emission scanning electron microscopy (FE-SEM, JSM-7001, JEOL Ltd., Japan) in backscattered electron mode. Meanwhile, energy dispersive X-ray spectroscopy (EDS, X-ManN, Oxford Instruments Co., England) was employed to determine the chemical composition of each phase distributed within the joint. 3 Results and discussion 3.1 Thermo-mechanical reliability of the SICA assemblies To evaluate the influence of mixed LMS/HMS filler on the thermo-mechanical reliability of LH-SICA, TQFP specimens prepared using L-SICA or LH-SICA were subjected to thermal shock testing. FE-SEM images of cross-sections of the TQFP joints soldered with L-SICA or LH-SICA before thermal shock testing in Fig. 3 show that the joints formed with both types of SICA contained wide and stable metallurgical conduction paths between the corresponding leads and electrodes owing to the internal flow, coalescence, and wetting behavior of the molten solder filler within the polymer. Furthermore, the conduction paths were covered by cured polymer (the outer boundary of cured polymer is denoted by a dotted line), which can enhance the mechanical strength of the SICA joint and protect the conduction path from external factors. As can be seen in Fig. 3 (a), the conduction path in L-SICA was formed through the internal flow of molten LMS filler, coalescence between adjacent molten LMS filler areas, and their wetting behavior on the electrode within the low-viscosity polymer. In contrast, as can be seen in Fig. 3 (b), the conduction path for the electrode was formed in LH-SICA owing to the flow and wetting behavior of molten LMS containing solid-state HMS filler within the low-viscosity polymer, with the final joint being created by the formation of a solid solution through the melting of solid HMS within the conduction path [ 19 , 20 ]. The conduction paths in both types of SICA exhibited similar and well-defined morphologies owing to proper conduction path formation. Therefore, the influence of the conduction path area on the reliability of the two types of SICA joints can be considered negligible. Figure 4 shows that electrical resistance in both SICA assemblies during thermal shock testing remained at approximately 2 Ω without noticeably changing during the entirety of thermal shock testing. The electrical resistance of an electronic package joint is influenced by the joint area. When fractures occur and propagate within the joint, the electrical resistance is increased because of the decreased effective joint area. Thus, stable electrical resistance indicates that the conduction paths in the SICA joints remained stable without failing even under the rapid temperature changes induced during the thermal shock testing. This can be attributed to the wide and stable metallurgical conduction path formed between the leads and electrodes on the TQFPs and PCB. Therefore, the SICA joint can achieve superior electrical reliability in harsh environments (regardless of whether adding HMS) due to the formation of a metallurgical conduction path. To evaluate any changes in the mechanical properties of the SICA assemblies during thermal shock testing, a 45° pull test was conducted on the TQFP joints. As can be seen in Fig. 5 , before thermal shock testing, the LH-SICA joint exhibited approximately 32.81% higher mechanical pull strength than that of the L-SICA joint (19.425 ± 0.867 vs. 14.646 ± 0.948 N). As confirmed in previous research [ 19 ], the improved mechanical interconnection properties of LH-SICA can be attributed to microstructural changes in the conduction path and the resulting reinforcing effect. The LMS in LH-SICA changed from a eutectic composition to a hypo-eutectic composition due to an increase in Sn content introduced by the HMS filler. As the mixed molten LMS/HMS filler solidified, fine Cu 6 Sn 5 and Ag 3 Sn IMCs formed through chemical reactions between the Sn, Cu, and Ag atoms therein, and as the temperature passed the liquidus line during cooling, the primary Sn-phase precipitated. Afterward, when the temperature was lowered below the eutectic isotherm, fine Bi-rich phases were precipitated owing to the decreased solubility of the Bi-phase in the Sn-phase. Thus, LH-SICA exhibits higher initial mechanical properties compared to L-SICA through a reinforcing effect (i.e., precipitation hardening and dispersion strengthening) provided by the distribution of fine IMCs (i.e., Cu 6 Sn 5 and Ag 3 Sn) and Bi-rich phase particles within the conduction path. As the number of thermal shock cycles was increased, the pull strength of both types of SICA decreased. This can be attributed to flattening of the interfacial IMC layer and increased brittleness due to excessive IMC growth or microstructure coarsening caused by accelerated diffusion of metal atoms under thermal shock [ 21 – 23 ]. Although the LH-SICA exhibited lower mechanical pull strength with an increase in the number of thermal shock cycles, it was still higher than that of L-SICA owing to the high initial bonding strength through the reinforcing effects of mixing the LMS and HMS fillers. After thermal shock testing, the mechanical pull strength of LH-SICA was approximately 78.81% higher than that of L-SICA. This confirms that LH-SICA with the mixed LMS/HMS filler has better thermo-mechanical reliability than L-SICA with the LMS filler only. Figure 3 Figure 4 Figure 5 3.2 Microstructure analysis To identify the cause of the better thermo-mechanical reliability of the LH-SICA joints, microstructural analysis was conducted on the cross-sections of the SICA joints. Figure 6 shows FE-SEM images of the interface IMCs formed between the conduction path and Cu electrode during thermal shock testing. Before thermal shock testing, a small and uniform scallop-shaped Cu 6 Sn 5 IMC layer was formed at the bonding interface of the SICA joints due to the chemical reaction between Sn atoms in the solder and Cu atoms in the electrode (i.e., 6Cu + 5Sn → Cu 6 Sn 5 ) [ 24 , 25 ]. In L-SICA, the Cu 6 Sn 5 IMC at the bonding interface was 1.277 ± 0.550 µm thick, and Bi-rich phases accumulated at the bulk solder/Cu 6 Sn 5 IMC interface due to the consumption of Sn atoms during the Cu 6 Sn 5 IMC formation [ 26 ]. In contrast, the Cu 6 Sn 5 IMC formed at the bonding interface of the LH-SICA joint was thicker (1.809 ± 1.032 µm) due to the higher reflow peak temperature required to melt the HMS filler, while noticeable accumulation of Bi-rich phases was observed at the bulk solder/ Cu 6 Sn 5 IMC interface. As the number of thermal shock cycles was increased, the thickness of the Cu 6 Sn 5 IMC layer at the SICA bonding interface gradually increased due to the acceleration of atom diffusion and the chemical reaction. Subsequently, a Cu 3 Sn IMC layer formed and grew at the Cu 6 Sn 5 IMC/Cu electrode interface owing to the solid-state interfacial reaction between the thickened interfacial Cu 6 Sn 5 IMC and Cu atoms in the electrode (i.e., 3Cu + Sn → Cu 3 Sn, and 9Cu + Cu 6 Sn 5 → 5Cu 3 Sn) [ 24 , 25 ]. Especially, in the L-SICA joint, the interfacial Cu 6 Sn 5 IMC changed from an initial thin scallop shape that became flatter and grew rapidly during thermal shock testing. This morphological change in the interfacial Cu 6 Sn 5 IMC is attributable to the faster growth of Cu 6 Sn 5 in the valleys between adjacent scallop shapes compared to the bulk Cu 6 Sn 5 phase due to the shorter diffusion length and time for Cu atoms [ 27 ]. In addition, the amount of the accumulated Bi-rich phase at the interface between the flattened Cu 6 Sn 5 IMC and the bulk solder significantly increased due to the rapid consumption of Sn atoms during the growth of the Cu 6 Sn 5 IMC. On the other hand, although the interfacial Cu 6 Sn 5 IMC that formed in LH-SICA was initially thicker than that in L-SICA due to the relatively higher reflow temperature, it grew more slowly during thermal shock testing and was thinner afterward (3.221 ± 0.447 vs. 4.114 ± 0.554 µm). Furthermore, the interface IMC in LH-SICA maintained a scallop shape with less morphological flattening compared to that in L-SICA. This can be attributed to the Ag 3 Sn IMC present at the bulk solder/Cu 6 Sn 5 IMC interface in LH-SICA. During interfacial IMC growth, Ag 3 Sn IMC particles located on the IMC interface act as barriers against the interdiffusion path of Cu and Sn atoms, thereby suppressing morphological transformation and excessive growth of the interfacial IMC layer [ 28 ]. In addition, no noticeable accumulation of Bi-rich phases at the bulk/Cu 6 Sn 5 IMC interface was observed during thermal shock testing. Changes in the thickness and growth rate of the interfacial IMCs in the SICA joints during thermal shock testing are shown in Fig. 7 . As can be seen in Fig. 7 (a), the interface IMC layer in the SICA joints became thicker with an increase in the number of thermal shock cycles. As previously mentioned, the interfacial IMC in the LH-SICA joint was initially thicker than that in L-SICA due to the relatively high reflow temperature required for HMS melting and the resulting higher atomic diffusion rate. However, although the interfacial IMC in L-SICA was initially thinner, its thickness increased rapidly with an increase in the number of thermal shock cycles, surpassing that in LH-SICA after approximately 300 cycles. As shown by the overall IMC growth rate according to the number of thermal shock testing cycles in Fig. 7 (b), the IMC growth rate in L-SICA was rapid and was approximately 220% larger, whereas that in LH-SICA was relatively slower and was approximately 78% larger by the end of the test. As can be seen in the FE-SEM images of the SICA joints in Fig. 8 , the microstructure of L-SICA before thermal shock testing exhibited a typical lamellar eutectic structure composed of repeatedly stacked Sn-rich (dark-gray) and Bi-rich (bright-gray) phases [ 29 ]. In contrast, this was not seen in the microstructure of the LH-SICA joint, while fine Cu 6 Sn 5 and Ag 3 Sn IMCs, and Bi-rich phase particles, were dispersed within the wide Sn-rich phase regions. As previously mentioned, the fine IMCs and Bi-rich phases distributed within the LH-SICA joint contributed to enhancing the mechanical interconnection properties therein by hindering dislocation and plastic deformation. During thermal shock testing, the microstructure of the L-SICA joint gradually lost its eutectic lamellar structure and coarsened as the number of thermal shock cycles was increased. In contrast, as the number of thermal shock cycles was increased, the microstructure of LH-SICA coarsened compared to its initial morphology, albeit to a lesser extent than seen in L-SICA. The microstructural coarsening of a solder joint is affected by thermal energy at high temperature and mechanical energy from repetitive or static stresses. The coarsening of the microstructure at high temperatures occurs through the thermal activation of atoms within the joints and the subsequent acceleration of atomic diffusion. Moreover, coarsening induced by mechanical energy is accelerated by plastic deformation owing to the internal stress. The plastic deformation creates numerous lattice defects such as dislocations and vacancies that act as additional diffusion paths for metal atoms, thereby further promoting the coarsening phenomenon [ 30 – 32 ]. Based on this mechanism, the reduced coarsening in the LH-SICA joint during thermal shock testing can be attributed to the initially formed fine microstructure by the mixed LMS/HMS filler; this improved the mechanical properties and subsequently reduced atomic diffusion in the joint, thereby reducing plastic deformation over repeated thermal shock cycles compared to L-SICA. The formation of a thin IMC layer formed by the atomic diffusion and interfacial chemical reaction between the bulk solder material and electrode is essential for achieving sufficient metallurgical bonding as well as reliable electrical and mechanical performance in the electronic device joint. However, excessive growth of the IMC layer deteriorates the performance and lifetime of solder joints because of its inherent brittleness and mismatches in the physical properties (e.g., the coefficient of thermal expansion, elastic modulus, and hardness) of the solder materials, IMCs, and electrode materials; this can have a detrimental effect on joint reliability by acting as an initiation point for brittle fracturing due to interfacial stress concentration [ 33 – 35 ]. In addition, the thermo-mechanical reliability of solder joints is affected not only by the thickness of the interface IMC but also by its morphology. A scallop-shaped IMC formed at the bulk solder/metallization interface can ensure superior bonding strength and thermo-mechanical reliability by suppressing of crack propagation owing to stress distribution. Contrarily, a flattened interfacial IMC layer due to the IMC growing facilitates crack propagation due to the reduced shear resistance, which causes the mechanical properties and lifetime of the solder joint to deteriorate more rapidly [ 36 , 37 ]. Moreover, as can be seen in the interfacial IMC morphology of the L-SICA joint (Fig. 6 ), the accumulated Bi-rich phase at the interface of the flattened Cu 6 Sn 5 IMC layer causes mechanical performance to deteriorate due to the inherent brittleness of Bi [ 38 ]. Our results indicate that the improvement in the thermo-mechanical reliability seen in LH-SICA compared to L-SICA is attributable to the initial high bonding properties due to the reinforcement effect of the mixed LMS/HMS filler, a reduction in microstructural coarsening caused by compositional change in the conduction path in the LH-SICA joint, suppressed growth and flattening of the interfacial IMC layer, and reduced brittleness due to a reduction in Bi-rich phases accumulated at the bulk solder/Cu 6 Sn 5 IMC interface. Figure 6 Figure 7 Figure 8 4 Conclusions We formulated two types of SICA (L-SICA with LMS filler and LH-SICA with mixed LMS/HMS filler) and evaluated the influence of the mixed LMS/HMS filler on the thermo-mechanical reliability of the subsequent SICA joints through thermal shock testing. The electrical performances of both SICA assemblies were stable throughout the entire thermal shock test owing to the formation of metallurgical conduction paths by the molten solder fillers between the corresponding leads and electrodes. Although the mechanical pull strength of both SICA assemblies decreased compared to the initial pull strength, LH-SICA exhibited better thermo-mechanical reliability than L-SICA as the number of thermal shock testing cycles was increased. This enhancement can be attributed to the initially achieved high bonding properties in LH-SICA caused by the reinforcing effect of the mixed LMS/HMS filler, the reduction of microstructural coarsening caused by compositional change in the conduction path, suppressed growth and flattening of the interfacial IMC layer, and reduced brittleness due to a reduction in Bi-rich phases accumulated at the bulk solder/Cu 6 Sn 5 IMC interface. The results of this study confirm that the mixed LMS/HMS filler can improve not only the initial bonding properties of a SICA joint but also its thermo-mechanical reliability. Declarations Acknowledgments This research was supported by the Chung-Ang University Graduate Research Scholarship in 2023. Author contributions YHB: conceptualization, methodology, investigation and writing the original draft; MJJ: visualization and investigation; JIL: methodology and investigation; JMK: supervision and validation; BSY: supervision and validation. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not- for-profit sectors. Data availability The datasets used or analyzed in this study are available with the corresponding author. They can be produced upon reasonable request. Conflict of interest The authors declare no known competing financial interests or personal relationships that can influence the work reported in this paper. References N. Jiang, L. Zhang, Z.Q. Liu, L. Sun, W.M. Long, P. He, M. Zhao, Sci. technol. Advan Mater. 20 , 876–901 (2019) N.M. Poon, C.L. Wu, J.K. Lai, Y.C. Chan, IEEE Trans. Adv. Package. 23 , 708–714 (2002) L. Zhang, S.B. Xue, L.L. Gao, Z. Sheng, S.L. Yu, Y. Chen, Z. Guang, Microelectron. Reliab. 50 , 2071–2077 (2010) W.W. Lee, L.T. Nguyen, G.S. Selvaduray, Microelectron. Reliab. 40 , 231–244 (2000) W. Ning, C. Zhu, H. Li, G. Xu, L. Luo, H. Guo, F. Jing, Mater. Sci. Semicon. Proc. 16, 933–939 (2013) R. Aradhana, S. Mohanty, S.K. Nayak, Int. J. Adhes. Adhes. 99 , 102596 (2020) Q. Wang, S. Zhang, G. Liu, T. Lin, P. He, J. Alloys Compd. 820 , 153184 (2020) W. Zhang, Z. Yao, H. Liu, J. Liu, M. Li, F. Li, H. Chen, Microelectron. Reliab. 151 , 115236 (2023) Y. Li, C.P. Wong, Mater. Sci. Eng: R: Rep. 51 , 1–35 (2006) Y. Guan, X. Chen, F. Li, H. Gao, Int. J. Adhes. Adhes. 30 , 80–88 (2010) R. Dudek, H. Berek, T. Fritsch, B. Michel, IEEE Trans. Compon. Packag Technol. 23 , 462–469 (2000) B.S. Yim, J.M. Kim, S.H. Jeon, S.H. Lee, J. Kim, J.G. Han, M. Cho, Mater. Trans. 50 , 2649–2655 (2009) B.S. Yim, J.I. Lee, B.H. Lee, Y.E. Shin, J.M. Kim, Microelectron. Reliab. 54 , 2944–2950 (2014) B.S. Yim, J.M. Kim, Microelectron. Reliab. 57 , 93–100 (2016) W.U. Ping, Trans. Nonferr Met. Soc. China. 25 , 1225–1233 (2015) F. Wang, Y. Huang, Z. Zhang, C. Yan, Mater. 10 , 920 (2017) A.K. Gain, L. Zhang, J. Mater. Sci. : Mater. Electron. 27 , 781–794 (2016) M.J. Ha, J.I. Lee, J.M. Kim, B. Seung Yim, J. Mater. Sci. : Mater. Electron. 34 , 890 (2023) M.J. Ha, J.I. Lee, J.M. Kim, B.S. Yim, J. Mater. Sci. : Mater. Electron. 34 , 1888 (2023) Y.H. Ha, J.I. Lee, J.M. Kim, B.S. Yim, J. Mater. Sci. : Mater. Electron. 35 , 1–14 (2024) B.S. Yim, J.M. Kim, J. Mater. Sci. : Mater. Electron. 27 , 9159–9171 (2016) T. An, F. Qin, Microelectron. Reliab. 54 , 932–938 (2014) M. Shang, C. Li, Y. Wang, X. Chen, Y. Zhao, J. Ke, J. Chen, J. Mater. Res. Technol. 33 , 6307–6318 (2024) F. Wang, H. Chen, Y. Huang, C. Yan, J. Mater. Sci. : Mater. Electron. 29 , 11409–11420 (2018) M.Y. Xiong, L. Zhang, J. Mater. Sci. 54 , 1741–1768 (2019) Q.S. Zhu, Z.F. Zhang, Z.G. Wang, J.K. Shang, J. Mater. Res. 23 , 78–82 (2008) R. Tian, C. Hang, Y. Tian, L. Zhao, Mater. Sci. Eng: A 709 , 125–133 (2018) W.N. Hsu, F.Y. Ouyang, Mater. Chem. Phy. 165 , 66–71 (2015) S. Zhou, C.H. Yang, Y.A. Shen, S.K. Lin, H. Nishikawa, Materialia. 6 , 100300 (2019) J.D. Robson, Metall. Mater. Trans. A 51 , 5401–5413 (2020) Y. Tian, N. Ren, Z. Zhao, F. Wu, S.K. Sitaraman, Materials. 11 , 2509 (2018) H. Conrad, Z. Gui, Y. Fahmy, D. Yang, J. Electron. Mater. 28 , 1062–1070 (1999) X. Wang, L. Zhang, X. Wang, Y.H. Guo, L. Sun, Y.X. Liu, X. Lu, J. Mater. Res. Technol. 21 , 4263–4280 (2022) A. Jalar, M.A. Bakar, R. Ismail, A.R. Daud, J. Sci. Res. Dev. 3 , 49–54 (2016) J.W. Yoon, S.B. Jung, J. Alloys Compd. 359 , 202–208 (2003) P.L. Tu, Y.C. Chan, J.K.L. Lai, IEEE Trans. Compon. Packag Manuf. Technol. B 20 , 87–93 (2002) Y.C. Chan, P.L. Tu, A.C. So, J.K.L. Lai, IEEE Trans. Compon. Packag Manuf. Technol. B 20 , 463–469 (2002) Q. Zhang, H. Zou, Z.F. Zhang, J. Mater. Res. 25 , 303–314 (2010) Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 21 Dec, 2025 Read the published version in Journal of Materials Science: Materials in Electronics → Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. 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12:12:08","extension":"html","order_by":29,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":88611,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/20e4e10113604c89ace248ec.html"},{"id":94856228,"identity":"e041eee1-1b3c-4c0e-b473-c98bc80088ce","added_by":"auto","created_at":"2025-10-31 12:12:07","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":331057,"visible":true,"origin":"","legend":"\u003cp\u003eSchematics of the conduction path formation mechanism in LH-SICA containing the LMS/HMS fillers. (a) The as-prepared material, (b) internal flow and coalescence behaviors of molten LMS, and integration between solid-state HMS and coalesced molten LMS on contact, (c) conduction path formation due to the wetting behavior of LMS containing solid-state HMS, and (d) completion of the conduction path formation owing to HMS melting and polymer curing.\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/0d84911c0e4fc3faa5eea6eb.png"},{"id":94856224,"identity":"fd6aecf8-9c8e-4d0c-b9ce-50b3a88a767a","added_by":"auto","created_at":"2025-10-31 12:12:07","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":172550,"visible":true,"origin":"","legend":"\u003cp\u003eReflow profiles for the bonding process using SICAs.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/6a619c45d9f9a8489e0c075f.png"},{"id":94856225,"identity":"3951c30c-8f5d-4ee2-9949-59be78d30ed5","added_by":"auto","created_at":"2025-10-31 12:12:07","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1761413,"visible":true,"origin":"","legend":"\u003cp\u003eFE-SEM images of the conduction paths formed in (a) L-SICA and (b) LH-SICA.\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/0552194842137c6f02f689a9.png"},{"id":94985768,"identity":"2804d97e-2595-4854-a145-23fba43e6b07","added_by":"auto","created_at":"2025-11-03 06:58:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":120742,"visible":true,"origin":"","legend":"\u003cp\u003eElectrical resistance changes in the SICA assemblies during thermal shock testing.\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/49bd44cfe3bbf93ef188dda1.png"},{"id":94856227,"identity":"6be8e063-79c3-4477-aec5-3c72990b427c","added_by":"auto","created_at":"2025-10-31 12:12:07","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":119028,"visible":true,"origin":"","legend":"\u003cp\u003eMechanical pull strength changes in the SICA assemblies during thermal shock testing.\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/19ea52a41d4ae9ce5a405d19.png"},{"id":94856232,"identity":"a8b147fa-e5e9-4f49-bf0c-5d06896db5d4","added_by":"auto","created_at":"2025-10-31 12:12:07","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2255404,"visible":true,"origin":"","legend":"\u003cp\u003eFE-SEM images of the interfacial IMC layers between the conduction path and Cu electrode in SICA joints during thermal shock testing.\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/6e738415850ea526a794f683.png"},{"id":94985812,"identity":"563bf7a0-afbc-48a9-9891-7b06176ca9c4","added_by":"auto","created_at":"2025-11-03 06:59:02","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":290610,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in the interfacial IMC layer between the conduction path and Cu electrode during thermal shock testing. (a) Total IMC layer thickness, and (b) IMC growth rate.\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/06533f05dc802aac12c52750.png"},{"id":94856236,"identity":"e7edc2eb-a543-44d6-8aff-d735b09637de","added_by":"auto","created_at":"2025-10-31 12:12:07","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":2210525,"visible":true,"origin":"","legend":"\u003cp\u003eFE-SEM images of the microstructure in LH-SICA joints during thermal shock testing.\u003c/p\u003e","description":"","filename":"Fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/a6788fa4a88e0ee96981e56b.png"},{"id":98815080,"identity":"0d532820-6973-4ddc-a87c-941245ca5964","added_by":"auto","created_at":"2025-12-22 16:13:31","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8360499,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7872022/v1/34d670a3-bd61-4adf-a60e-5c0919be3e66.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Improving the thermo-mechanical reliability of solderable isotropic conductive adhesive joints by using low- and high-melting-point solder fillers","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eHigh functionalization, high integration, and miniaturization of electronic packages have been accelerated in the electronic package industry [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. When electronic packages comprising various materials with different coefficients of thermal expansion (CTEs) are exposed to harsh environments (e.g., thermal shock or repetitive thermal fluctuations induced by power consumption or external environmental changes), CTE mismatches between package materials induce high interfacial stresses, which can lead to crack initiation and propagation. Ultimately, this causes the entire electronic package to lose its functionality via interface delamination and fracturing [\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Therefore, overcoming this thermo-mechanical reliability issue is critical importance in the electronic package industry [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAmong the interconnection materials for electronic packages, conventional electrically conductive adhesives (ECAs) containing polymer resin and non-fusible metal fillers have been extensively studied as an alternative to lead-free solder because of advantages such as low-temperature processing, process simplification, fine-pitch capability, eco-friendliness, and compatibility with various materials [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, despite these advantages, the use of conventional ECAs is limited because of issues such as low electrical stability, thermal durability, and low shock and joint strength due to their conduction mechanism: electrically interconnecting the two electrodes through the physical contact of non-fusible fillers [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Moreover, contact between the metal filler and electrodes can be lost due to moisture absorption by the polymer, weakened adhesion in a high-temperature/high-humidity environment, and/or repeated thermal shock, thus making it difficult to ensure the reliability of the ECA joint [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eTo overcome these problems, research has been conducted on solderable isotropic conductive adhesives (SICAs) composed of a polymer with fluxing capability and a fusible low-melting-point solder (LMS) filler [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. SICAs solve the problems of conventional ECAs by forming a metallurgical conduction path between the leads and electrodes through internal flow and coalescence of the molten LMS, as well as wetting behavior of the coalesced LMS on the electrodes within the polymer during the reflow process. Moreover, this provides better mechanical interconnection properties than those of commercial solder joints due to the reinforcing effect of the cured polymer surrounding the conduction path.\u003c/p\u003e\u003cp\u003eTo form a suitably wide and stable conduction path with in the SICA interconnection process, it is essential to use an LMS filler with a lower melting point than the curing temperature of the thermosetting polymer. To this end, Sn\u0026ndash;58Bi eutectic solder with a melting point of 139 ℃ is commonly used as an LMS filler in the synthesis of typical SICAs. However, the resulting solder joint has problems with interconnection properties and reliability due to several issues, such as low ductility caused by the brittle nature of Bi, coarsening of the Bi-phase within the bulk solder, rapid growth of the intermetallic compound (IMC) in the bonding interface, and accompanying segregation of the Bi-phase [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eTo overcome these problems, we previously fabricated and investigated a mixed LMS/high-melting-point-solder (HMS) filler filled SICA (LH-SICA) [\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the conduction path formation mechanism in LH-SICA. During the reflow process, the molten LMS filler disperses within the polymer by flowing and coalescing inside the low-viscosity polymer while the solid-state HMS filler is simultaneously absorbed through contact with the molten LMS filler. Meanwhile, the wetting behavior of the combination forms a metallurgical conduction path between the leads and electrodes. When the temperature reaches the melting point of the HMS fillers, it melts and forms a solid solution with the molten LMS filler, with bonding completed by fully curing polymer. Our investigation confirmed that the joint formed with LH-SICA achieved better mechanical interconnection properties than that of a SICA containing an LMS filler only (L-SICA) due to the reinforcing effect (including precipitation hardening and dispersion strengthening effects) by fine IMCs (i.e., Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e and Ag\u003csub\u003e3\u003c/sub\u003eSn) and Bi-rich phase particles dispersed within the conduction path.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the present work, we fabricated thin quad flat package (TQFP) assemblies containing L-SICA (with LMS filler) and LH-SICA (with mixed LMS/HMS filler. Afterward, we investigated the thermo-mechanical reliability of SICA joints using these materials via thermal shock testing, during which we evaluated the electrical and mechanical performances of both SICA assemblies.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials\u003c/h2\u003e\u003cp\u003eThe SICA assemblies used in this study contained a polymer composite functionalized with fluxing capability and a fusible solder filler for the formation of metallurgical conduction paths and electrical connections. In the formulation of the polymer composite, thermosetting epoxy diglycidyl ether of bisphenol A (DGEBA), 4,4'-diaminodiphenylmethane (DDM), and boron trifluoro-mono-ethylamine (BF\u003csub\u003e3\u003c/sub\u003eMEA) were used as the base resin, curing agent, and catalyst, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Carboxylic acid was used as a fluxing agent to remove the oxide layer on the electrodes and metal fillers during the reflow process. Sn\u0026ndash;58Bi (with a melting point of 139 ℃) and Sn\u0026ndash;3.0Ag\u0026ndash;0.5Cu (with a melting point of 219 ℃) were used as the LMS and HMS fillers, respectively. Both had a mean particle diameter of 38 \u0026micro;m.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eComponents of the proposed LH-SICAs\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eComponents\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eL-SICA\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eLH-SICA\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003ePolymer\u003c/p\u003e\u003cp\u003ecomposite\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBase resin\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eDGEBA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCuring agent\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eDDM\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCatalyst\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eBF3MEA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eReductant\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eCarboxylic acid\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eFusible filler\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLMS\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eSn-58Bi (φ 38 \u0026micro;m)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHMS\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eSn\u0026ndash;3Ag\u0026ndash;0.5Cu (φ: 38 \u0026micro;m)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLMS/HMS mixing ratio (vol%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e100:0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e50:50\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFor the reliability testing, TQFP (TQFP44T30, Topline Co., USA) assemblies (12 \u0026times; 12 \u0026times; 1.2 mm\u003csup\u003e3\u003c/sup\u003e) were prepared with 44 Sn-plated leads (11 attached to each side of the TQFP body) with a lead pitch of 0.8 mm. Printed circuit boards (PCBs) (32 \u0026times; 32 \u0026times; 1.0 mm\u003csup\u003e3\u003c/sup\u003e) were equipped with bare Cu electrodes (without surface finish) plated to a thickness of 18 \u0026micro;m. Daisy chains of solder joints were formed on the TQFPs and PCBs to measure the electrical reliability of the SICA assemblies during the reliability testing.\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Test method\u003c/h2\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e2.2.1 Preparation of test assessment\u003c/h2\u003e\u003cp\u003eTo evaluate the influence of the mixed LMS/HMS filler on thermo-mechanical reliability of SICA, L-SICA containing only LMS filler, and LH-SICA containing a mixed LMS/HMS filler (volume fraction (vol%) between LMS and HMS: 50:50) were synthesized. The total solder filler content within the SICA assemblies was set to 30 vol% to form a wide and stable conduction path between the leads and electrodes. To create TQFP interconnections using the SICA assemblies, a metal mask (100 \u0026micro;m in thickness) was aligned and mounted on the cleaned PCB, and a uniform amount of SICA was applied to the exposed electrodes using the squeegee method. After completing SICA application, the TQFP leads were aligned and mounted onto the corresponding electrodes using a flip-chip bonding machine (LAMBDA, Finetech Co., Germany), and the reflow process was carried out according to the reflow profiles shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The L-SICA specimens were reflowed from room temperature to 180 ℃ at a heating rate of 120 ℃ min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and held at the peak temperature for approximately 2 min to cure the polymer composite. The LH-SICA specimens were heated from room temperature to 240 ℃ at the same heating rate to melt the HMS filler, and held at the peak temperature for approximately 2 min. Afterward, to confirm the morphology of the conduction paths created therein, the specimens were cross-sectioned and then observed under an optical microscope (VHX-1000, Keyence Co., Japan).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.2.2 Reliability testing\u003c/h2\u003e\u003cp\u003eTo investigate the influence of the mixed LMS/HMS filler on the thermo-mechanical reliability of SICA joints in harsh environments, thermal shock testing was conducted in a thermal shock chamber (TSE-11-A, Espec Corp., Japan). In accordance with JEDEC standard JESD22-A106B C, both SICA assemblies were exposed to repetitive thermal fluctuations from \u0026minus;\u0026thinsp;55 ℃ to 125 ℃ 1000 cycles. Each cycle lasted 30 minutes (with a dwell time of 15 minutes at each peak temperature); the transfer time between peak temperatures was 10 s, and the heating and cooling rates were both approximately 18\u0026deg;C s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eTo measure any changes in electrical performance during the thermal shock test, the electrical resistance of the SICA joints was measured using a multimeter (34410A, Agilent Tech., USA). Subsequently, changes in the mechanical properties of the SICA joints during the thermal shock test were determined via 45\u0026deg; pull testing on the TQFP leads using a pull tester (PTR-1000, Rhesca Co., Japan). In accordance with JEDEC standard JIS Z 3198-6, the TQFP specimens were clamped in the pull tester apparatus at 45\u0026deg;, and then the TQFP leads were pulled upward at a pull rate of 6 mm min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e2.2.3 Microstructure analysis\u003c/h2\u003e\u003cp\u003eTo investigate any microstructural changes and interfacial IMC layer growth between the conduction path and electrodes in the SICA joints, they were examined after specific numbers of thermal shock cycles (i.e., 0, 200, 500, and 1000 cycles) during the thermal shock testing. Beforehand, the SICA specimens were cross-sectioned by grinding using silicon carbide paper and subsequently polished with a 3 \u0026micro;m diamond suspension. The cross-sectioned surfaces were then etched for 10 s using an etching solution of 90% methanol and 10% nitric acid to clearly reveal the phase boundaries of the IMC and the microstructure of the SICA joints. The specimens were then examined using field emission scanning electron microscopy (FE-SEM, JSM-7001, JEOL Ltd., Japan) in backscattered electron mode. Meanwhile, energy dispersive X-ray spectroscopy (EDS, X-ManN, Oxford Instruments Co., England) was employed to determine the chemical composition of each phase distributed within the joint.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Thermo-mechanical reliability of the SICA assemblies\u003c/h2\u003e\u003cp\u003eTo evaluate the influence of mixed LMS/HMS filler on the thermo-mechanical reliability of LH-SICA, TQFP specimens prepared using L-SICA or LH-SICA were subjected to thermal shock testing. FE-SEM images of cross-sections of the TQFP joints soldered with L-SICA or LH-SICA before thermal shock testing in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e show that the joints formed with both types of SICA contained wide and stable metallurgical conduction paths between the corresponding leads and electrodes owing to the internal flow, coalescence, and wetting behavior of the molten solder filler within the polymer. Furthermore, the conduction paths were covered by cured polymer (the outer boundary of cured polymer is denoted by a dotted line), which can enhance the mechanical strength of the SICA joint and protect the conduction path from external factors. As can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a), the conduction path in L-SICA was formed through the internal flow of molten LMS filler, coalescence between adjacent molten LMS filler areas, and their wetting behavior on the electrode within the low-viscosity polymer. In contrast, as can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b), the conduction path for the electrode was formed in LH-SICA owing to the flow and wetting behavior of molten LMS containing solid-state HMS filler within the low-viscosity polymer, with the final joint being created by the formation of a solid solution through the melting of solid HMS within the conduction path [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The conduction paths in both types of SICA exhibited similar and well-defined morphologies owing to proper conduction path formation. Therefore, the influence of the conduction path area on the reliability of the two types of SICA joints can be considered negligible.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows that electrical resistance in both SICA assemblies during thermal shock testing remained at approximately 2 Ω without noticeably changing during the entirety of thermal shock testing.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe electrical resistance of an electronic package joint is influenced by the joint area. When fractures occur and propagate within the joint, the electrical resistance is increased because of the decreased effective joint area. Thus, stable electrical resistance indicates that the conduction paths in the SICA joints remained stable without failing even under the rapid temperature changes induced during the thermal shock testing. This can be attributed to the wide and stable metallurgical conduction path formed between the leads and electrodes on the TQFPs and PCB. Therefore, the SICA joint can achieve superior electrical reliability in harsh environments (regardless of whether adding HMS) due to the formation of a metallurgical conduction path.\u003c/p\u003e\u003cp\u003eTo evaluate any changes in the mechanical properties of the SICA assemblies during thermal shock testing, a 45\u0026deg; pull test was conducted on the TQFP joints. As can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, before thermal shock testing, the LH-SICA joint exhibited approximately 32.81% higher mechanical pull strength than that of the L-SICA joint (19.425\u0026thinsp;\u0026plusmn;\u0026thinsp;0.867 vs. 14.646\u0026thinsp;\u0026plusmn;\u0026thinsp;0.948 N). As confirmed in previous research [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], the improved mechanical interconnection properties of LH-SICA can be attributed to microstructural changes in the conduction path and the resulting reinforcing effect. The LMS in LH-SICA changed from a eutectic composition to a hypo-eutectic composition due to an increase in Sn content introduced by the HMS filler. As the mixed molten LMS/HMS filler solidified, fine Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e and Ag\u003csub\u003e3\u003c/sub\u003eSn IMCs formed through chemical reactions between the Sn, Cu, and Ag atoms therein, and as the temperature passed the liquidus line during cooling, the primary Sn-phase precipitated. Afterward, when the temperature was lowered below the eutectic isotherm, fine Bi-rich phases were precipitated owing to the decreased solubility of the Bi-phase in the Sn-phase. Thus, LH-SICA exhibits higher initial mechanical properties compared to L-SICA through a reinforcing effect (i.e., precipitation hardening and dispersion strengthening) provided by the distribution of fine IMCs (i.e., Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e and Ag\u003csub\u003e3\u003c/sub\u003eSn) and Bi-rich phase particles within the conduction path. As the number of thermal shock cycles was increased, the pull strength of both types of SICA decreased. This can be attributed to flattening of the interfacial IMC layer and increased brittleness due to excessive IMC growth or microstructure coarsening caused by accelerated diffusion of metal atoms under thermal shock [\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Although the LH-SICA exhibited lower mechanical pull strength with an increase in the number of thermal shock cycles, it was still higher than that of L-SICA owing to the high initial bonding strength through the reinforcing effects of mixing the LMS and HMS fillers. After thermal shock testing, the mechanical pull strength of LH-SICA was approximately 78.81% higher than that of L-SICA. This confirms that LH-SICA with the mixed LMS/HMS filler has better thermo-mechanical reliability than L-SICA with the LMS filler only.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Microstructure analysis\u003c/h2\u003e\u003cp\u003eTo identify the cause of the better thermo-mechanical reliability of the LH-SICA joints, microstructural analysis was conducted on the cross-sections of the SICA joints. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows FE-SEM images of the interface IMCs formed between the conduction path and Cu electrode during thermal shock testing. Before thermal shock testing, a small and uniform scallop-shaped Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC layer was formed at the bonding interface of the SICA joints due to the chemical reaction between Sn atoms in the solder and Cu atoms in the electrode (i.e., 6Cu\u0026thinsp;+\u0026thinsp;5Sn \u0026rarr; Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. In L-SICA, the Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC at the bonding interface was 1.277\u0026thinsp;\u0026plusmn;\u0026thinsp;0.550 \u0026micro;m thick, and Bi-rich phases accumulated at the bulk solder/Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC interface due to the consumption of Sn atoms during the Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC formation [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. In contrast, the Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC formed at the bonding interface of the LH-SICA joint was thicker (1.809\u0026thinsp;\u0026plusmn;\u0026thinsp;1.032 \u0026micro;m) due to the higher reflow peak temperature required to melt the HMS filler, while noticeable accumulation of Bi-rich phases was observed at the bulk solder/ Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC interface.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAs the number of thermal shock cycles was increased, the thickness of the Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC layer at the SICA bonding interface gradually increased due to the acceleration of atom diffusion and the chemical reaction. Subsequently, a Cu\u003csub\u003e3\u003c/sub\u003eSn IMC layer formed and grew at the Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC/Cu electrode interface owing to the solid-state interfacial reaction between the thickened interfacial Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC and Cu atoms in the electrode (i.e., 3Cu\u0026thinsp;+\u0026thinsp;Sn \u0026rarr; Cu\u003csub\u003e3\u003c/sub\u003eSn, and 9Cu\u0026thinsp;+\u0026thinsp;Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e \u0026rarr; 5Cu\u003csub\u003e3\u003c/sub\u003eSn) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Especially, in the L-SICA joint, the interfacial Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC changed from an initial thin scallop shape that became flatter and grew rapidly during thermal shock testing. This morphological change in the interfacial Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC is attributable to the faster growth of Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e in the valleys between adjacent scallop shapes compared to the bulk Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e phase due to the shorter diffusion length and time for Cu atoms [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. In addition, the amount of the accumulated Bi-rich phase at the interface between the flattened Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC and the bulk solder significantly increased due to the rapid consumption of Sn atoms during the growth of the Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC. On the other hand, although the interfacial Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC that formed in LH-SICA was initially thicker than that in L-SICA due to the relatively higher reflow temperature, it grew more slowly during thermal shock testing and was thinner afterward (3.221\u0026thinsp;\u0026plusmn;\u0026thinsp;0.447 vs. 4.114\u0026thinsp;\u0026plusmn;\u0026thinsp;0.554 \u0026micro;m). Furthermore, the interface IMC in LH-SICA maintained a scallop shape with less morphological flattening compared to that in L-SICA. This can be attributed to the Ag\u003csub\u003e3\u003c/sub\u003eSn IMC present at the bulk solder/Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC interface in LH-SICA. During interfacial IMC growth, Ag\u003csub\u003e3\u003c/sub\u003eSn IMC particles located on the IMC interface act as barriers against the interdiffusion path of Cu and Sn atoms, thereby suppressing morphological transformation and excessive growth of the interfacial IMC layer [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. In addition, no noticeable accumulation of Bi-rich phases at the bulk/Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC interface was observed during thermal shock testing.\u003c/p\u003e\u003cp\u003eChanges in the thickness and growth rate of the interfacial IMCs in the SICA joints during thermal shock testing are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. As can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a), the interface IMC layer in the SICA joints became thicker with an increase in the number of thermal shock cycles. As previously mentioned, the interfacial IMC in the LH-SICA joint was initially thicker than that in L-SICA due to the relatively high reflow temperature required for HMS melting and the resulting higher atomic diffusion rate. However, although the interfacial IMC in L-SICA was initially thinner, its thickness increased rapidly with an increase in the number of thermal shock cycles, surpassing that in LH-SICA after approximately 300 cycles. As shown by the overall IMC growth rate according to the number of thermal shock testing cycles in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b), the IMC growth rate in L-SICA was rapid and was approximately 220% larger, whereas that in LH-SICA was relatively slower and was approximately 78% larger by the end of the test.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAs can be seen in the FE-SEM images of the SICA joints in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the microstructure of L-SICA before thermal shock testing exhibited a typical lamellar eutectic structure composed of repeatedly stacked Sn-rich (dark-gray) and Bi-rich (bright-gray) phases [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. In contrast, this was not seen in the microstructure of the LH-SICA joint, while fine Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e and Ag\u003csub\u003e3\u003c/sub\u003eSn IMCs, and Bi-rich phase particles, were dispersed within the wide Sn-rich phase regions. As previously mentioned, the fine IMCs and Bi-rich phases distributed within the LH-SICA joint contributed to enhancing the mechanical interconnection properties therein by hindering dislocation and plastic deformation. During thermal shock testing, the microstructure of the L-SICA joint gradually lost its eutectic lamellar structure and coarsened as the number of thermal shock cycles was increased. In contrast, as the number of thermal shock cycles was increased, the microstructure of LH-SICA coarsened compared to its initial morphology, albeit to a lesser extent than seen in L-SICA.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe microstructural coarsening of a solder joint is affected by thermal energy at high temperature and mechanical energy from repetitive or static stresses. The coarsening of the microstructure at high temperatures occurs through the thermal activation of atoms within the joints and the subsequent acceleration of atomic diffusion. Moreover, coarsening induced by mechanical energy is accelerated by plastic deformation owing to the internal stress. The plastic deformation creates numerous lattice defects such as dislocations and vacancies that act as additional diffusion paths for metal atoms, thereby further promoting the coarsening phenomenon [\u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Based on this mechanism, the reduced coarsening in the LH-SICA joint during thermal shock testing can be attributed to the initially formed fine microstructure by the mixed LMS/HMS filler; this improved the mechanical properties and subsequently reduced atomic diffusion in the joint, thereby reducing plastic deformation over repeated thermal shock cycles compared to L-SICA.\u003c/p\u003e\u003cp\u003eThe formation of a thin IMC layer formed by the atomic diffusion and interfacial chemical reaction between the bulk solder material and electrode is essential for achieving sufficient metallurgical bonding as well as reliable electrical and mechanical performance in the electronic device joint. However, excessive growth of the IMC layer deteriorates the performance and lifetime of solder joints because of its inherent brittleness and mismatches in the physical properties (e.g., the coefficient of thermal expansion, elastic modulus, and hardness) of the solder materials, IMCs, and electrode materials; this can have a detrimental effect on joint reliability by acting as an initiation point for brittle fracturing due to interfacial stress concentration [\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. In addition, the thermo-mechanical reliability of solder joints is affected not only by the thickness of the interface IMC but also by its morphology.\u003c/p\u003e\u003cp\u003eA scallop-shaped IMC formed at the bulk solder/metallization interface can ensure superior bonding strength and thermo-mechanical reliability by suppressing of crack propagation owing to stress distribution. Contrarily, a flattened interfacial IMC layer due to the IMC growing facilitates crack propagation due to the reduced shear resistance, which causes the mechanical properties and lifetime of the solder joint to deteriorate more rapidly [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Moreover, as can be seen in the interfacial IMC morphology of the L-SICA joint (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), the accumulated Bi-rich phase at the interface of the flattened Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC layer causes mechanical performance to deteriorate due to the inherent brittleness of Bi [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOur results indicate that the improvement in the thermo-mechanical reliability seen in LH-SICA compared to L-SICA is attributable to the initial high bonding properties due to the reinforcement effect of the mixed LMS/HMS filler, a reduction in microstructural coarsening caused by compositional change in the conduction path in the LH-SICA joint, suppressed growth and flattening of the interfacial IMC layer, and reduced brittleness due to a reduction in Bi-rich phases accumulated at the bulk solder/Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC interface.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eWe formulated two types of SICA (L-SICA with LMS filler and LH-SICA with mixed LMS/HMS filler) and evaluated the influence of the mixed LMS/HMS filler on the thermo-mechanical reliability of the subsequent SICA joints through thermal shock testing. The electrical performances of both SICA assemblies were stable throughout the entire thermal shock test owing to the formation of metallurgical conduction paths by the molten solder fillers between the corresponding leads and electrodes. Although the mechanical pull strength of both SICA assemblies decreased compared to the initial pull strength, LH-SICA exhibited better thermo-mechanical reliability than L-SICA as the number of thermal shock testing cycles was increased. This enhancement can be attributed to the initially achieved high bonding properties in LH-SICA caused by the reinforcing effect of the mixed LMS/HMS filler, the reduction of microstructural coarsening caused by compositional change in the conduction path, suppressed growth and flattening of the interfacial IMC layer, and reduced brittleness due to a reduction in Bi-rich phases accumulated at the bulk solder/Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC interface. The results of this study confirm that the mixed LMS/HMS filler can improve not only the initial bonding properties of a SICA joint but also its thermo-mechanical reliability.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Chung-Ang University Graduate Research Scholarship in 2023.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYHB: conceptualization, methodology, investigation and writing the original draft; MJJ: visualization and investigation; JIL: methodology and investigation; JMK: supervision and validation; BSY: supervision and validation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not- for-profit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used or analyzed in this study are available with the corresponding author. They can be produced upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e The authors declare no known competing financial interests or personal relationships that can influence the work reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eN. Jiang, L. Zhang, Z.Q. Liu, L. Sun, W.M. Long, P. He, M. Zhao, Sci. technol. Advan Mater. \u003cb\u003e20\u003c/b\u003e, 876\u0026ndash;901 (2019)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eN.M. Poon, C.L. Wu, J.K. Lai, Y.C. Chan, IEEE Trans. Adv. Package. \u003cb\u003e23\u003c/b\u003e, 708\u0026ndash;714 (2002)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eL. Zhang, S.B. Xue, L.L. Gao, Z. Sheng, S.L. Yu, Y. Chen, Z. Guang, Microelectron. Reliab. \u003cb\u003e50\u003c/b\u003e, 2071\u0026ndash;2077 (2010)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eW.W. Lee, L.T. Nguyen, G.S. Selvaduray, Microelectron. Reliab. \u003cb\u003e40\u003c/b\u003e, 231\u0026ndash;244 (2000)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eW. Ning, C. Zhu, H. Li, G. Xu, L. Luo, H. Guo, F. Jing, Mater. Sci. Semicon. Proc. 16, 933\u0026ndash;939 (2013)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eR. Aradhana, S. Mohanty, S.K. Nayak, Int. J. Adhes. Adhes. \u003cb\u003e99\u003c/b\u003e, 102596 (2020)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eQ. Wang, S. Zhang, G. Liu, T. Lin, P. He, J. Alloys Compd. \u003cb\u003e820\u003c/b\u003e, 153184 (2020)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eW. Zhang, Z. Yao, H. Liu, J. Liu, M. Li, F. Li, H. Chen, Microelectron. Reliab. \u003cb\u003e151\u003c/b\u003e, 115236 (2023)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eY. Li, C.P. Wong, Mater. Sci. Eng: R: Rep. \u003cb\u003e51\u003c/b\u003e, 1\u0026ndash;35 (2006)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eY. Guan, X. Chen, F. Li, H. Gao, Int. J. Adhes. Adhes. \u003cb\u003e30\u003c/b\u003e, 80\u0026ndash;88 (2010)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eR. Dudek, H. Berek, T. Fritsch, B. Michel, IEEE Trans. Compon. Packag Technol. \u003cb\u003e23\u003c/b\u003e, 462\u0026ndash;469 (2000)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eB.S. Yim, J.M. Kim, S.H. Jeon, S.H. Lee, J. Kim, J.G. Han, M. Cho, Mater. Trans. \u003cb\u003e50\u003c/b\u003e, 2649\u0026ndash;2655 (2009)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eB.S. Yim, J.I. Lee, B.H. Lee, Y.E. Shin, J.M. Kim, Microelectron. Reliab. \u003cb\u003e54\u003c/b\u003e, 2944\u0026ndash;2950 (2014)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eB.S. Yim, J.M. Kim, Microelectron. Reliab. \u003cb\u003e57\u003c/b\u003e, 93\u0026ndash;100 (2016)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eW.U. Ping, Trans. Nonferr Met. Soc. China. \u003cb\u003e25\u003c/b\u003e, 1225\u0026ndash;1233 (2015)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eF. Wang, Y. Huang, Z. Zhang, C. Yan, Mater. \u003cb\u003e10\u003c/b\u003e, 920 (2017)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eA.K. Gain, L. Zhang, J. Mater. Sci. : Mater. Electron. \u003cb\u003e27\u003c/b\u003e, 781\u0026ndash;794 (2016)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eM.J. Ha, J.I. Lee, J.M. Kim, B. Seung Yim, J. Mater. Sci. : Mater. Electron. \u003cb\u003e34\u003c/b\u003e, 890 (2023)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eM.J. Ha, J.I. Lee, J.M. Kim, B.S. Yim, J. Mater. Sci. : Mater. Electron. \u003cb\u003e34\u003c/b\u003e, 1888 (2023)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eY.H. Ha, J.I. Lee, J.M. Kim, B.S. Yim, J. Mater. Sci. : Mater. Electron. \u003cb\u003e35\u003c/b\u003e, 1\u0026ndash;14 (2024)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eB.S. Yim, J.M. Kim, J. Mater. Sci. : Mater. Electron. \u003cb\u003e27\u003c/b\u003e, 9159\u0026ndash;9171 (2016)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eT. An, F. Qin, Microelectron. Reliab. \u003cb\u003e54\u003c/b\u003e, 932\u0026ndash;938 (2014)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eM. Shang, C. Li, Y. Wang, X. Chen, Y. Zhao, J. Ke, J. Chen, J. Mater. Res. Technol. \u003cb\u003e33\u003c/b\u003e, 6307\u0026ndash;6318 (2024)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eF. Wang, H. Chen, Y. Huang, C. Yan, J. Mater. Sci. : Mater. Electron. \u003cb\u003e29\u003c/b\u003e, 11409\u0026ndash;11420 (2018)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eM.Y. Xiong, L. Zhang, J. Mater. Sci. \u003cb\u003e54\u003c/b\u003e, 1741\u0026ndash;1768 (2019)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eQ.S. Zhu, Z.F. Zhang, Z.G. Wang, J.K. Shang, J. Mater. Res. \u003cb\u003e23\u003c/b\u003e, 78\u0026ndash;82 (2008)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eR. Tian, C. Hang, Y. Tian, L. Zhao, Mater. Sci. Eng: A \u003cb\u003e709\u003c/b\u003e, 125\u0026ndash;133 (2018)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eW.N. Hsu, F.Y. Ouyang, Mater. Chem. Phy. \u003cb\u003e165\u003c/b\u003e, 66\u0026ndash;71 (2015)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eS. Zhou, C.H. Yang, Y.A. Shen, S.K. Lin, H. Nishikawa, Materialia. \u003cb\u003e6\u003c/b\u003e, 100300 (2019)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJ.D. Robson, Metall. Mater. Trans. A \u003cb\u003e51\u003c/b\u003e, 5401\u0026ndash;5413 (2020)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eY. Tian, N. Ren, Z. Zhao, F. Wu, S.K. Sitaraman, Materials. \u003cb\u003e11\u003c/b\u003e, 2509 (2018)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eH. Conrad, Z. Gui, Y. Fahmy, D. Yang, J. Electron. Mater. \u003cb\u003e28\u003c/b\u003e, 1062\u0026ndash;1070 (1999)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eX. Wang, L. Zhang, X. Wang, Y.H. Guo, L. Sun, Y.X. Liu, X. Lu, J. Mater. Res. Technol. \u003cb\u003e21\u003c/b\u003e, 4263\u0026ndash;4280 (2022)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eA. Jalar, M.A. Bakar, R. Ismail, A.R. Daud, J. Sci. Res. Dev. \u003cb\u003e3\u003c/b\u003e, 49\u0026ndash;54 (2016)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJ.W. Yoon, S.B. Jung, J. Alloys Compd. \u003cb\u003e359\u003c/b\u003e, 202\u0026ndash;208 (2003)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eP.L. Tu, Y.C. Chan, J.K.L. Lai, IEEE Trans. Compon. Packag Manuf. Technol. B \u003cb\u003e20\u003c/b\u003e, 87\u0026ndash;93 (2002)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eY.C. Chan, P.L. Tu, A.C. So, J.K.L. Lai, IEEE Trans. Compon. Packag Manuf. Technol. B \u003cb\u003e20\u003c/b\u003e, 463\u0026ndash;469 (2002)\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eQ. Zhang, H. Zou, Z.F. Zhang, J. Mater. Res. \u003cb\u003e25\u003c/b\u003e, 303\u0026ndash;314 (2010)\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"high melting point solder, low melting point solder, polymer composites, reliability, solderable isotropic conductive adhesive","lastPublishedDoi":"10.21203/rs.3.rs-7872022/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7872022/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, we investigated the effect of adding a mixed low-melting-point solder (LMS)/high-melting-point-solder (HMS) filler on the thermo-mechanical reliability of solderable isotropic conductive adhesive (SICA) joints. To this end, we compared the properties and thermo-mechanical reliability of L-SICA (fabricated with LMS filler) and LH-SICA (fabricated with the mixed LMS/HMS filler). LH-SICA exhibited enhanced mechanical interconnection properties compared with L-SICA due to precipitation hardening and dispersion strengthening effects arising from the distribution of intermetallic compounds (IMCs) Ag\u003csub\u003e3\u003c/sub\u003eSn and Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e, and Bi-rich phase particles within the joint. The results of thermal shock testing revealed that the electrical reliability of both SICA assemblies remained stable owing to the formation of a metallurgical conduction path between the corresponding leads and electrodes through the molten solder filler. Although the pull strength of SICA assemblies tended to decrease compared with their initial pull strength during thermal shock testing, LH-SICA exhibited improved thermo-mechanical reliability compared with L-SICA. This is due to the enhanced bonding properties, a reduction in microstructural coarsening, slower growth and flattening of the IMC layer at the bonding interface, and a reduction in the accumulated Bi-rich phase at the bulk solder/Cu\u003csub\u003e6\u003c/sub\u003eSn\u003csub\u003e5\u003c/sub\u003e IMC interface resulting from changes in the composition of the LH-SICA joint.\u003c/p\u003e","manuscriptTitle":"Improving the thermo-mechanical reliability of solderable isotropic conductive adhesive joints by using low- and high-melting-point solder fillers","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-31 12:12:02","doi":"10.21203/rs.3.rs-7872022/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"6c184585-5e18-4a1f-b6a9-5ff42803d566","owner":[],"postedDate":"October 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-22T16:08:39+00:00","versionOfRecord":{"articleIdentity":"rs-7872022","link":"https://doi.org/10.1007/s10854-025-16417-z","journal":{"identity":"journal-of-materials-science-materials-in-electronics","isVorOnly":false,"title":"Journal of Materials Science: Materials in Electronics"},"publishedOn":"2025-12-21 15:58:08","publishedOnDateReadable":"December 21st, 2025"},"versionCreatedAt":"2025-10-31 12:12:02","video":"","vorDoi":"10.1007/s10854-025-16417-z","vorDoiUrl":"https://doi.org/10.1007/s10854-025-16417-z","workflowStages":[]},"version":"v1","identity":"rs-7872022","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7872022","identity":"rs-7872022","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}