Electroless Ni-P Deposition on Flexible Polyimide Substrates with Tin-Palladium nucleation

Electroless Ni-P Deposition on Flexible Polyimide Substrates with Tin-Palladium nucleation | 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 Electroless Ni-P Deposition on Flexible Polyimide Substrates with Tin-Palladium nucleation Marcelo Kioshi Hirata, Andreia de Morais, Alexander Flacker, Michele Odnicki da Silva, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6147604/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Feb, 2026 Read the published version in Journal of Materials Science: Materials in Engineering → Version 1 posted You are reading this latest preprint version Abstract The purpose of this study is to report a low-cost electroless deposition (ED) process of Ni-P thin film using wet technology on flexible polyimide substrate (Kapton® 300HN DuPont™), comprising functionalization with NaOH, nucleation with Sn and Pd and acceleration with HCl. The pretreatment performed on the polyimide surface was investigate using a contact angle system and attenuated total reflection Fourier-transform infrared spectroscopy. Structural, morphological and electrical characterization of the Ni-P film were performed by X-ray diffraction spectroscopy, stylus scan profiler, scanning electron microscopy, X-ray photoelectron spectroscopy and four-point probe measurements. The characterization showed that the treatment of the flexible polyimide enables a high performance in ED, delivering a very compact spherical nano-structured film without holes, scratches and flaws, with particle size ranging from 380 to 780 nm. polyimide Ni-P electroless deposition flexible substrate Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction Nowadays, flexible electronics are widely spreading due to its portability and compatibility with arbitrary-shaped and curved surfaces. 1,2 High selectivity and environment friendly procedures for surface metallization (such as additive methods) are preferred for manufacturing such devices because of the reduced consumption of metal materials. 1,3,4 Flexible polyimide substrates, commonly known by the brand name Kapton®, are versatile materials often used for fabricating flexible electronic circuitry because they are excellent insulators, capable of preventing the flow of electrical current. 2 Polyimide is also known for its high-temperature resistance. It can withstand elevated temperatures, up to 400 ºC without degrading, making it a valuable insulator for components that generate heat, such as in the aerospace and automotive industries. 5 Polyimide also has good dielectric properties, meaning it can separate conductive materials and prevent electrical discharge. In addition, polyimide can be flexible and can be easily conformable into the shape of electronic components. 6 Interests in wet-process surface modification of polyimides have increased due to simplicity and low cost. Polyimide films are resistant to most solvents and chemicals, but they react with oxidizing or reducing agents. However, if the concentration of the chemical reagents, reaction temperatures and reaction time are well controlled, the reactions can be confined to the surface. 7 Electroless deposition (ED) technique is an important metallization method for non- conductive materials and its use is increasing for a wide range of commercial applications. 6,8,9 It was found to be very useful for interconnection applications on several micro technology assemblies and offers high selectivity that allows self-aligned deposition, hence reducing the needs for lithography steps. ED methods are also very versatile and can produce multi component films. In addition, many metals and alloys can be deposited as thin films with good quality. 10 Other advantages of ED are high metal purity, low operating temperature, planar topography, low cost and applicability for mass production. 11 For most polymers, including polyimide, the ED process requires a pretreatment before surface metallization. The purpose of the pretreatment is to generate sufficient nucleation sites for the metal atoms to deposit. There is a full sort of process routes to this end, for instance, polyimide surface modification has been achieved by means of immersion on NaOH/HNO 3 12 or KOH 7,13 solutions, via plasma treatment 1 or more complex techniques using different baths compositions 1,7,12,13,14 associated with heat treatments 14 or vacuum drying 7 . Another possible route is to use of PdCl 2 /SnCl 2 catalyst solutions, which has already been demonstrated for other types of nonmetallic substrates by our research group 15,16,17 and others 18 . Herein, we investigated a pretreatment based on the use of NaOH and PdCl 2 /SnCl 2 solutions using only low temperatures, to modify the surface of a polyimide substrate and achieve a high rate ED of Ni-P. The main advantage of the process presented here relies on the use of a pure wet method, with lower thermal expenses than the ones reported in previous studies using NaOH for functionalization of polyimides 14 . Experimental Materials Polyimide substrate, NaOH (≥ 99%), SnCl 2 ⋅2H 2 O, PdCl 2 and HCl (36.0-38.0%) were purchased from Merck (PA ACS, Darmstadt, Germany). NiSO 4 ⋅6H 2 O, NaH 2 PO 2 ⋅H 2 O, CH 3 COONa⋅3H 2 O were purchased from Synth (PA-ACS, Diadema, SP, Brazil). Pb(NO 3 ) 2 and NH 4 Cl were purchased from Vetec Quimica Fina Ltda (PA, Duque de Caxias, RJ, Brazil) and Cinética (PA, Jandira, SP, Brazil), respectively. All chemical reagents were of analytical grade and used as received. Surface pretreatment of the polyimide sample Flexible polyimide (Kapton ® 300HN DuPont™), with a size of 50 mm × 50 mm × 0.08 mm was used as reference substrate material. The surface pretreatment of polyimide consisted of three stages: functionalization, nucleation (catalyzing and reducing steps), and acceleration processes. For functionalization, the samples were immersed in a NaOH solution under magnetic stirring during a few minutes at the following temperatures: 25, 30, 40, 50 or 60 °C. NaOH excess was removed by rinsing with de-ionized (DI) water (18 MΩ cm) during 5 min. As for the nucleation step, the functionalized polyimide substrate was seeded with Pd by immersion in an acidic SnCl 2 solution followed by an immersion in acidic PdCl 2 solution, with a temperature range between 22-25 °C. Each immersion lasted about 15 to 30 s and was followed by washing the samples by immersion in distilled water. Finally, the sample was dipped in an accelerating solution consisting of 10% HCl. After nucleation, a non-commercial autocatalytic solution of electroless Ni-P, reported by Flacker et al . 15 was used. The deposition was performed at 50 °C, at a controlled pH of 5-5.3 by addition of NaOH and mechanical agitation. Table 1 shows the reagents, concentration and conditions of the solution used for electroless Ni-P deposition on polyimide surface. Table 1 . Ni-P bath composition. Compound Concentration / (g L -1 ) NiCl 2. 6H 2 O 15 NaH 2 PO 2 .H 2 O 30 CH 2 C 2 OONa 10 NH 4 Cl 50 Pb(NO 3 ) 2 0.004 Characterization The following techniques and equipment were used to characterize the polyimide surfaces: contact angle OCA 15 plus (Dataphysics Instrument GmbH Filderstadt, Germany); infrared spectra (FTIR) Spectrum 100 (PerkinElmer) range 4000-550 cm -1 ; X-ray photoelectron spectroscopy (XPS) measurements were carried out on a Thermo Scientific K-Alpha spectrometer (Brno, Czech Republic) equipped with monochromatized Al-Ka radiation (1486 eV). Binding energies for all peaks were calibrated by the C 1s peak at 284.8 eV. The background in high resolution spectra was computed by the Shirley method. The high-resolution XPS spectra were deconvoluted using a weighted sum of Lorentzian and Gaussian components curves. The XPS data were analyzed using CasaXPS software (Casa Software, Ltd., UK, version 2.3 25PR1.0). Samples thicknesses were estimated with a Dektak XT scan profiler (Bruker, Billerica, USA). X-ray diffraction (XRD) was performed with a Shimadzu LabX XRD-6000 on an operating voltage of 40 kV with a current of 30 mA and Cu Kα radiation (1.5406 Å), with 2θ from 10 to 80°. Scanning electron microscopy images and energy dispersive spectroscopy (EDS) data were obtained with a field emission gun scanning electron microscope (SEM-FEG) (MIRA 3 XMU model, TESCAN, Brno, Czech Republic) coupled with Bruker Quantax System EDS. The sheet Resistance values of the substrate were estimated at using four-point probe (Thin Film Devices, INC, FPP-2000). Results and Discussion Flexible polyimide substrates are of great interested of the microelectronics field, since this material can be used as substrate for the assembly of flexible electronic devices. 19 This material also has an excellent thermal stability from -273 °C up to 400 °C and good dielectric properties. 20 In this work, the proposed pretreatment process before plating the polyimide involving three stages: ( i ) formation of polar functional groups. This step adds new functions on the surface to enable the next step: the pretreatment is necessary because electroless deposition onto insulator materials demands the formation of seeds onto the surface. ( ii ) Nucleation (catalyzing and reducing). In this step, a redox reaction takes place between Pd 2+ and Sn 2+ on the substrate where Pd 2+ is reduced to Pd 0 to catalyze the following steps: 21 , 22 , 15 , 23 With this, the Pd/Sn sites created on the pretreatment leads to the formation of the Pd seeds, which will enable the nucleation and growth of NiP particles during the ED process. ( iii ) acceleration process, where the excess of ionic tin from colloid-covered surface, which surrounds the palladium catalyst, is removed. 24 , 16 ( iv ) ED process, using a Ni-P containing bath. Figure 1a shows the scheme of the polyimide reaction after the pretreatment and deposition of the metallic film through the wet process (acceleration process is not represented in this Figure because it only removes the excess Sn). Figure 1b shows a photography sequence of the ED process. Mechanistically, it has been proposed that the funcionalization step leads to the introduction of OH - groups in the surface of polyimide, which would then work as sites for attachment of Pd 2+ ions. After the reducing step, Pd 0 would be generated, which would act as seed layer for Ni-P deposition. 25 Then, once the seed layer has been formed, metallic Ni is deposited during ED process according to equation 1, while elemental phosphorus is co-deposited according to equation 2. Other byproducts such as hydrogen gas are also produced, as shown in equation 3. 25 Since the pretreatment was observed to be crucial to enable successful ED of Ni-P onto the polyimide substrate, a detailed characterization of the substrate surface before and after pretreatment was performed, as discussed below. Characterization of the polyimide substrate after surface pretreatment FTIR spectra of the polyimide surface before and after treatment with NaOH are shown in Figure 2. The characteristic absorption bands of untreated polyimide surface were assigned to N-H stretch (3481 cm -1 ) of amine groups; C-H in aromatic stretch (3100-3000 cm -1 ); asymmetrical and symmetrical C=O stretch (1780 and 1708 cm -1 ), -NH 2 deformation bending (1604 cm -1 ), aromatic ring C=C bending (1500 cm -1 ), and C-N imide group (1373 cm -1 ). 26 The polyimide surface was pretreated with NaOH solution to enhance the wettability and the concentration of polar functional groups (e.g., -OH group). As seen from the FTIR spectrum of polyimide substrates treated with NaOH solution (4 min at 25, 30, 40, 50, and 60 °C), the absorption bands assigned to O-H stretching bands (3700-3100 cm -1 ) increase with increasing surface treatment temperature. It indicates that the pretreatment with NaOH solution introduced oxygen-containing functional groups on the polyimide surface. We verified experimentally that this would then affect the adherence of the Ni-P film, with best results obtained in the 30-40 °C range (determined by simple 3M Scotch Tape adhesion tests). When the pretreatment was performed at 25 °C, the Ni-P film deposited in the subsequent steps was not uniform (flaws were observed, suggesting an incomplete substrate coverage). On the other hand, when higher temperatures (50-60 ºC) were used in this step, the Ni-P film would adhere very poorly on the polyimide surface. This behavior was thus correlated to the increase in the amide C=O content on the polyimide surface after functionalization using higher temperatures (see the signal at 1650 cm ‑1 ), which seems to interact poorly with the metal elements, this leading to poorer adhesion. XPS technique was also used to investigate the chemical composition of the polyimide surface, before and after treatment with NaOH solution (4 min at 30 °C). Survey XPS spectrum (see Figure 3a) of the pristine polyimide sample consists of C (80.7%), O (14.2%), and N (5.5%). Typical high-resolution XPS spectra of carbon (C 1s) and oxygen (O 1s) atomic core levels are presented in Figures 3b and 3c. High-resolution C 1s XPS spectrum of the pristine polyimide substrate was deconvoluted into four main peaks assigned to C-C (53.7%), C-N (28.5%), C-O (7.4%), and C=O (10.4%) bonding, respectively. High-resolution O 1s XPS spectrum was deconvoluted into two main peaks attributed to C=O (71.5%) and C-O (28.5%) bonding, respectively. 27 , 28 Figure 3d shows the survey XPS spectrum of the polyimide sample after surface treatment with NaOH solution, indicating the presence of chemical elements C (70.5%), O (20.7%), N (5.5%), and Na (3.3%). High-resolution XPS spectra of C 1s and O 1s atomic core levels of this sample are presented in the Figures 3e and 3f. The same signals observed in the Figures 3b and 3c were found for the polyimide sample with surface treatment. In the high-resolution C 1s XPS spectrum (see Figure 3e), the signals referring to C-O (14.6%) and C=O (11.9%) chemical bonds were more pronounced. In addition, a new signal localized at 535.4 eV referring to the C-OH (3.2%) chemical bond was observed in the high-resolution O 1s XPS spectrum (see Figure 3f), indicating the incorporation of hydroxyl groups on the surface of the polyimide substrate after surface treatment with NaOH solution, in agreement with FTIR data. Water contact angle measurements were then performed to evaluate the wettability of the polyimide surface after surface treatment with NaOH solution. Contact angle images of pristine polyimide substrate showed that the surface before pretreatment was hydrophobic, so the drop does not spread over the surface, presenting a contact angle of ca. 69° (Figure 4a). After the pretreatment using an aqueous NaOH solution (4 min at 25, 30 and 40 °C), the contact angle reduced to approximately 25° and the drop greatly spread on the treated surface (Figure 4b, 4c, 4d). It indicates that the wettability on the polyimide surface increased with surface treatment with NaOH solution, due to the increased concentration of hydroxyl groups on its surface, as observed from XPS and FTIR. At 50 °C, the contact angle becomes larger (32°) this behavior can also be attributed to the formation of other functionalization groups on the polyimide surface, and this can reduce the adhesion of the Ni-P film, as observed in adhesion tests performed with an adhesive tape. The treatment at 30 °C resulted in the smaller contact angle (23° Figure 4c) and therefore this temperature was chosen for the subsequent study. Structural, morphological, and electrical characterization of Ni-P/ polyimide samples Figure 5a presents the variation of Ni-P film thickness as a function of the deposition time on the polyimide substrate pretreated with NaOH solution at 30 °C for 4 min. The Ni-P deposition rate was 122.1 nm min -1 , as calculated from the slope of the linear regression, as shown in the inset of Figure 5. Interestingly, this deposition rate is close to that obtained using for Ni-P platting on polyethylene terephthalate (112.2 nm min -1 ), as reported in our previous work 17 . A high deposition rate corroborates the success of the surface pretreatment applied to the polyimide. Figure 5b presents the variation of Ni-P film sheet resistance and its standard deviation as a function of the deposition time on the polyimide substrate. As expected, these measurements show a very fast decline in the sheet resistance value as the time of deposition rises due to the thickness enhancement, but the standard deviation also decreases, which suggests that the deposition is more uniform in longer deposition times. The polyimide substrates are naturally insulators, so the sheet resistance obtained after only 2 min of deposition is still high, about 856 W/sq. However, this value decreases exponentially upon enhancing the deposition time, reaching a value of 131 W/sq at 6 min and 69 W/sq at 10 min. Figure 6a displays the XRD patterns of polyimide samples, with and without surface treatment and after the electroless Ni-P process, for a 6 min deposition time. This time was fixed for further investigations because the Ni-P film thickness at this condition is around 1 µm, a thickness that has been used as reference by our group in metallization processes. XRD pattern of the pristine polyimide sample shows that three prominent signals can be clearly observed at 2θ = 14.2°, 21.9°, and 26.0° due to some crystallinity of the substrate. 29 , 30 No change in the diffractogram profile was detected after surface treatment with NaOH. The presence of the amorphous Ni-P film deposited on the polyimide surface was detected from the appearance of a broad signal ranging from 40° to 50°, in which this signal centered at 2θ = 45° corresponds to Ni(111) plane. 31 , 32 Figure 6b shows the surface roughness profile measured by a profilometer for the polyimide substrates: untreated, with surface treatment, and with Ni-P film deposited by electroless process. The average surface roughness of the pristine polyimide substrate (black line) was about 42.7 nm. After surface treatment (red line), the average surface roughness decreased to 34.2 nm, indicating a slight change in the morphology on the polyimide surface. After electroless Ni-P deposition the average roughness increased to 110.9 nm, suggesting the nucleation and growth of small Ni-P grains. The SEM images in Figure 7a show the surface morphology of the Ni-P film deposited was uniform, with compact spherical nano-structures, without holes and scratches, and no flaws. We observed that the growth of the film occurred in the form of agglomerates with particles sizes ranging from 380 to 780 nm (Figure 7b). The EDS analysis showed a high purity film, with a high Ni concentration (~90 at%) and about 10 at% phosphorous (see Figure 7c,d). This corresponds to approximately 94 wt% of Ni and 6 wt% of P. Other works that used NaOH pretreatment of polyimide substrates, with different procedures for the catalyzing/reducing and ED steps, using higher temperatures, obtained similar Ni-P alloys with roughly 92 wt% Ni and 8 wt% P 14 . Finally, the adherence of Ni-P films on Kapton was tested via bending tests, which showed no visible cracking or film delamination (see Figure 8). From the test, we observed that the Ni-P film deposited on the flexible polyimide substrate has good mechanical stability, maintaining its integrity and adherence to the polyimide after the bending test. The FTIR, XPS and contact angle results confirm and demonstrate the effectiveness of the pretreatment process on the polyimide surface, and the conditions that enable the wet process electroless deposition. Thickness, XRD, SEM, EDS and 4-point probe data are also consistent with each other and demonstrate that the deposited metallic layer can be obtained in a uniform and adherent film with properties suitable for use in electronic devices. Conclusions In this study, we investigated the deposition of Ni-P thin layer on the surface of the flexible polyimide through a wet surface pretreatment using only low temperatures (30°C and 50°C), providing a low-cost alternative to other more expensive methods previously reported in the literature. This adherent layer might be used as seed for the growth of other metallic films, such as gold, aiming at electronic circuit applications, thus being a versatile method besides being fast and of low cost. The characterization of Ni-P deposited samples showed that the treatment of the flexible polyimide enables a high performance in ED, with a deposition rate of 122.1 nm min − 1 , and delivering a compact spherically-shaped nano-structured film without holes, scratches and flaws, with particles sizes ranging from 380 to 780 nm, and high purity, with 9:1 Ni:P atomic ratio. The sheet resistance of the samples decreased to 69 Ω/sq for Ni-P films deposited for 10 min. With such value, it´s possible to fabricate structures such as Wheatstone bridges which, combined with another materials and/or functionalization, can lead to sensors/detectors of various physical parameters, like temperature, pressure and/or moisture among others. Declarations Acknowledgments The authors gratefully acknowledge PCI/CTI/CNPq (301232/2024-5 and 301216/2024-0), National Council for Scientific and Technological Development (CNPq, 409215/2023-6), São Paulo Research Foundation (FAPESP, 2017/11986-5), Shell and Brazilian Innovation Agency (FINEP 0139/21) for scholarships and financial support. The authors also thank Dr. José Maria Clemente da Silva Filho for the XRD measurements and Rafael de Godoi Machado for the XPS measurement at the Center for Innovation on New Energies (CINE). Research supported by CTI-Nano, strategic laboratory from SisNano, MCTI and financed by CNPq. Author Contributions Alex contributed with the following roles: Conceptualization, data curation, formal analysis, investigation, methodology, project administration, resources, supervision, validation, visualization, writing – original draft and writing – review & editing. Andréia contributed with the following roles: data curation, formal analysis, investigation, validation, visualization, and writing – review & editing. Marcelo contributed with the following roles: data curation, formal analysis, investigation, validation, visualization, writing – original draft and writing – review & editing. Michele contributed with the following roles: data curation, formal analysis, investigation, resources, validation, visualization and writing – review & editing. Jilian contributed with the following roles: formal analysis, funding acquisition, visualization, writing – review & editing. Ricardo contributed with the following roles: formal analysis, funding acquisition, project administration, resources, supervision, visualization, writing – review & editing. Conflict of Interest Statement Authors certify that they have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript. Data and Code Availability Not Applicable Supplementary Information Not Applicable Ethical Approval Not Applicable References Xiang, J.; Zhou, G.; Hong, Y.; He, W.; Wang, S.; Chen, Y.; Wang, C.; Tang, Y.; Sun, Y.; Zhu, Y.; Appl Surf Sci 2022 , 587 , 152848. 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[https://doi.org/10.1088/0268-1242/16/2/311] Prajwal, K.; Dey, A.; Sudhakar, M.; Nandi, A.; Esther, A. C. M.; Sridhara, N.; Yougandar, B.; Kumar, P.; Arya, S. B.; Rajendra, A.; J Mater Eng Perform 2019 , 28 , 5820. [https://doi.org/10.1007/s11665-019-04289-4] Buchtík, M.; Krystỳnová, M.; Másilko, J.; Wasserbauer, J.; Coatings 2019 , 9 , 461. [https://doi.org/10.3390/coatings9070461] Seifzadeh, D.; Kazemi Mohsenabadi, H.; Rajabalizadeh, Z.; RSC Adv 2016 , 6 , 97241. [https://doi.org/10.1039/c6ra19984d] Supplementary Files GraphicalAbstractGA.png Cite Share Download PDF Status: Published Journal Publication published 07 Feb, 2026 Read the published version in Journal of Materials Science: Materials in Engineering → 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. 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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-6147604","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":432342722,"identity":"6fc053fe-eb3c-48f3-a006-96abf1f9aae9","order_by":0,"name":"Marcelo Kioshi Hirata","email":"","orcid":"","institution":"Centro de Tecnologia da Informacao Renato Archer","correspondingAuthor":false,"prefix":"","firstName":"Marcelo","middleName":"Kioshi","lastName":"Hirata","suffix":""},{"id":432342723,"identity":"b44405fb-6439-4da1-a756-5b97cee0f6ac","order_by":1,"name":"Andreia de Morais","email":"","orcid":"","institution":"Centro de Tecnologia da Informacao Renato Archer","correspondingAuthor":false,"prefix":"","firstName":"Andreia","middleName":"","lastName":"de Morais","suffix":""},{"id":432342724,"identity":"7aa0fd46-3438-40da-a259-0af270cf1ef4","order_by":2,"name":"Alexander Flacker","email":"","orcid":"","institution":"Centro de Tecnologia da Informacao Renato Archer","correspondingAuthor":false,"prefix":"","firstName":"Alexander","middleName":"","lastName":"Flacker","suffix":""},{"id":432342725,"identity":"1bbbbab3-dab5-4de5-85dd-f64afd490acb","order_by":3,"name":"Michele Odnicki da Silva","email":"","orcid":"","institution":"Centro de Tecnologia da Informacao Renato Archer","correspondingAuthor":false,"prefix":"","firstName":"Michele","middleName":"Odnicki da","lastName":"Silva","suffix":""},{"id":432342726,"identity":"cfeed969-70e6-4180-ad5e-02b2193257a4","order_by":4,"name":"Jilian Nei de Freitas","email":"","orcid":"","institution":"Centro de Tecnologia da Informacao Renato Archer","correspondingAuthor":false,"prefix":"","firstName":"Jilian","middleName":"Nei","lastName":"de Freitas","suffix":""},{"id":432342727,"identity":"e9c50541-f98a-4c6f-89f0-a1a7893d1048","order_by":5,"name":"Ricardo Cotrin Teixeira","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtUlEQVRIiWNgGAWjYNACAwY5EHXgAZHqGRuAWozBWhKI18LAkAgiGIjSYt5++PjjioI76fPDDj8E2mInp9tAQIvMmbTExjMGz3I33k4zAGpJNjY7QECLhASPYWODweHcjbMTQFoOJG4jVku64ez0D6RpSZCXziHWFp60xJlALYYbpHMKDiQYEOMX9sMHPjb8OSwvPzt984cPFXZyBLXAgQFYpQGxykFAvoEU1aNgFIyCUTCiAAB6uUVEu8A7GwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-5443-2605","institution":"INPE: Instituto Nacional de Pesquisas Espaciais","correspondingAuthor":true,"prefix":"","firstName":"Ricardo","middleName":"Cotrin","lastName":"Teixeira","suffix":""}],"badges":[],"createdAt":"2025-03-03 15:32:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6147604/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6147604/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s40712-025-00376-8","type":"published","date":"2026-02-07T15:58:07+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":79664085,"identity":"801e1931-9412-465d-bcc3-1f62737b87d6","added_by":"auto","created_at":"2025-04-01 10:00:04","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":515561,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Scheme of polyimide surface pretreatment (functionalization), catalyzing and reducing steps, and the electroless Ni-P deposition on the surface.\u003csup\u003e \u003c/sup\u003e(b) Photo sequence of Ni-P deposition on the flexible Kapton\u003csup\u003e®\u003c/sup\u003e substrate: (1) Kapton substrate after catalyzing and reducing steps; (2) Electroless Ni-P deposition process (time: \u0026lt; 1 min); (3) Electroless Ni-P deposition process (time: 6 min); (4) final product: flexible Ni-P/Kapton\u003csup\u003e®\u003c/sup\u003e substrate.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/376059fb42ffcafd978d0018.png"},{"id":79662428,"identity":"8725383e-6d2e-4b5b-a397-59d87b8b9e37","added_by":"auto","created_at":"2025-04-01 09:52:04","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":307850,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of flexible polyimide substrate treated with NaOH solution for 4 min at different temperatures.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/9ff27c8598cf135ca2edd5e7.png"},{"id":79664088,"identity":"6b716a2d-ba4f-42ca-902a-b488548f95d5","added_by":"auto","created_at":"2025-04-01 10:00:04","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":424440,"visible":true,"origin":"","legend":"\u003cp\u003eSurvey XPS spectra and high-resolution XPS spectra of C 1s peak and O 1s peak of the polyimide samples, without and with surface treatment (NaOH, 4 min at 30 °C).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/3138ee1bbe7e819b51df165a.png"},{"id":79662427,"identity":"6ad1b45e-2c04-4f0b-86c1-5470a7163388","added_by":"auto","created_at":"2025-04-01 09:52:04","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":216313,"visible":true,"origin":"","legend":"\u003cp\u003eContact angle of polyimide surface: (a) untreated, and treated with NaOH solution \u003cbr\u003e\n(4 min) at (b) 25 °C; (c) 30 °C; (d) 40 °C; (e) 50 °C.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/5c64801822905d4c82f40fb1.png"},{"id":79662418,"identity":"2b0228f8-dead-4f36-b25d-c610476537dc","added_by":"auto","created_at":"2025-04-01 09:52:04","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":60743,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Deposition rate of Ni-P film on the polyimide substrate. (b) Sheet resistance as a function of the Ni-P deposition time on flexible polyimide substrates.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/e22ff6eea4fa2148c0266df3.png"},{"id":79662426,"identity":"8e5597c9-e222-4ec1-80d4-6cdc8eead345","added_by":"auto","created_at":"2025-04-01 09:52:04","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":211386,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XRD patterns and (b) surface roughness profile of the polyimide samples: (black line) untreated, (red line) with surface treatment and (blue line) after electroless Ni-P process using 6 min of deposition time.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/18e34b0182746343207d9ede.png"},{"id":79665227,"identity":"c71c512c-feba-4433-ad86-a9c8474be9df","added_by":"auto","created_at":"2025-04-01 10:08:04","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":635995,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of Ni-P film on polyimide surface with scale bars representing (a) 50 mm and (b) 2 mm. (c) EDS elemental spectrum of the same sample. (d) Quantification results of EDS analysis for Ni-P films on the flexible Kapton® substrate.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/eb9abfca136abbadaa0c84a6.png"},{"id":79662429,"identity":"1a63deb5-dad4-478f-8667-96bd327d643c","added_by":"auto","created_at":"2025-04-01 09:52:04","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":378218,"visible":true,"origin":"","legend":"\u003cp\u003eBending test of Ni-P film deposited by electroless process on flexible Kapton\u003csup\u003e® \u003c/sup\u003esubstrate: (a) Before bending; (b) bending; (c) after bending. Sample size is 50x50mm.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/411291907dd5c71ef9a74447.png"},{"id":102234328,"identity":"fcacbd88-1a4a-47bf-aa2d-9cda21c56132","added_by":"auto","created_at":"2026-02-09 16:10:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3607401,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/131002ba-6013-4012-a305-df01dbd1792e.pdf"},{"id":79665226,"identity":"469f269e-0059-47be-a191-e6459ece37fc","added_by":"auto","created_at":"2025-04-01 10:08:04","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":439236,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstractGA.png","url":"https://assets-eu.researchsquare.com/files/rs-6147604/v1/a4334061db8852f916c3b547.png"}],"financialInterests":"","formattedTitle":"Electroless Ni-P Deposition on Flexible Polyimide Substrates with Tin-Palladium nucleation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eNowadays, flexible electronics are widely spreading due to its portability and compatibility with arbitrary-shaped and curved surfaces.\u003csup\u003e1,2\u003c/sup\u003e High selectivity and environment friendly procedures for surface metallization (such as additive methods) are preferred for manufacturing such devices because of the reduced consumption of metal materials.\u003csup\u003e1,3,4\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eFlexible polyimide substrates, commonly known by the brand name Kapton\u0026reg;, are versatile materials often used for fabricating flexible electronic circuitry because they are excellent insulators, capable of preventing the flow of electrical current.\u003csup\u003e2\u003c/sup\u003e Polyimide is also known for its high-temperature resistance. It can withstand elevated temperatures, up to 400 \u0026ordm;C without degrading, making it a valuable insulator for components that generate heat, such as in the aerospace and automotive industries.\u003csup\u003e5\u003c/sup\u003e Polyimide also has good dielectric properties, meaning it can separate conductive materials and prevent electrical discharge. In addition, polyimide can be flexible and can be easily conformable into the shape of electronic components.\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eInterests in wet-process surface modification of polyimides have increased due to simplicity and low cost. Polyimide films are resistant to most solvents and chemicals, but they react with oxidizing or reducing agents. However, if the concentration of the chemical reagents, reaction temperatures and reaction time are well controlled, the reactions can be confined to the surface.\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eElectroless deposition (ED) technique is an important metallization method for non- conductive materials and its use is increasing for a wide range of commercial applications.\u003csup\u003e6,8,9\u003c/sup\u003e It was found to be very useful for interconnection applications on several micro technology assemblies and offers high selectivity that allows self-aligned deposition, hence reducing the needs for lithography steps. ED methods are also very versatile and can produce multi component films. In addition, many metals and alloys can be deposited as thin films with good quality.\u003csup\u003e10\u003c/sup\u003e Other advantages of ED are high metal purity, low operating temperature, planar topography, low cost and applicability for mass production.\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eFor most polymers, including polyimide, the ED process requires a pretreatment before surface metallization. The purpose of the pretreatment is to generate sufficient nucleation sites for the metal atoms to deposit. There is a full sort of process routes to this end, for instance, polyimide surface modification has been achieved by means of immersion on NaOH/HNO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e12\u003c/sup\u003e or KOH\u003csup\u003e7,13\u003c/sup\u003e solutions, via plasma treatment\u003csup\u003e1\u003c/sup\u003e or more complex techniques using different baths compositions\u003csup\u003e1,7,12,13,14\u003c/sup\u003e associated with heat treatments\u003csup\u003e14\u003c/sup\u003e or vacuum drying\u003csup\u003e7\u003c/sup\u003e. Another possible route is to use of PdCl\u003csub\u003e2\u003c/sub\u003e/SnCl\u003csub\u003e2\u003c/sub\u003e catalyst solutions, which has already been demonstrated for other types of nonmetallic substrates by our research group\u003csup\u003e15,16,17\u003c/sup\u003eand others\u003csup\u003e18\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHerein, we investigated a pretreatment based on the use of NaOH and PdCl\u003csub\u003e2\u003c/sub\u003e/SnCl\u003csub\u003e2\u003c/sub\u003e solutions using only low temperatures, to modify the surface of a polyimide substrate and achieve a high rate ED of Ni-P. The main advantage of the process presented here relies on the use of a pure wet method, with lower thermal expenses than the ones reported in previous studies using NaOH for functionalization of polyimides \u003csup\u003e14\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Experimental","content":"\u003ch2\u003eMaterials\u003c/h2\u003e\n\u003cp\u003ePolyimide substrate, NaOH (\u0026ge; 99%), SnCl\u003csub\u003e2\u003c/sub\u003e\u0026sdot;2H\u003csub\u003e2\u003c/sub\u003eO, PdCl\u003csub\u003e2\u003c/sub\u003e and HCl (36.0-38.0%) were purchased from Merck (PA ACS, Darmstadt, Germany). NiSO\u003csub\u003e4\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO, NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e\u0026sdot;H\u003csub\u003e2\u003c/sub\u003eO, CH\u003csub\u003e3\u003c/sub\u003eCOONa\u0026sdot;3H\u003csub\u003e2\u003c/sub\u003eO were purchased from Synth (PA-ACS, Diadema, SP, Brazil). Pb(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e and NH\u003csub\u003e4\u003c/sub\u003eCl were purchased from Vetec Quimica Fina Ltda (PA, Duque de Caxias, RJ, Brazil) and Cin\u0026eacute;tica (PA, Jandira, SP, Brazil), respectively. All chemical reagents were of analytical grade and used as received.\u003c/p\u003e\n\u003ch2\u003eSurface pretreatment of the polyimide sample\u003c/h2\u003e\n\u003cp\u003eFlexible polyimide (Kapton\u003csup\u003e\u0026reg;\u003c/sup\u003e 300HN DuPont\u0026trade;), with a size of 50 mm \u0026times; 50 mm \u0026times; 0.08 mm was used as reference substrate material. The surface pretreatment of polyimide consisted of three stages: functionalization, nucleation (catalyzing and reducing steps), and acceleration processes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor functionalization, the samples were immersed in a NaOH solution under magnetic stirring during a few minutes at the following temperatures: 25, 30, 40, 50 or 60 \u0026deg;C. NaOH excess was removed by rinsing with de-ionized (DI) water (18 MΩ cm) during 5 min. As for the nucleation step, the functionalized polyimide substrate was seeded with Pd by immersion in an acidic SnCl\u003csub\u003e2\u003c/sub\u003e solution followed by an immersion in acidic PdCl\u003csub\u003e2\u003c/sub\u003e solution, with a temperature range between 22-25 \u0026deg;C. Each immersion lasted about 15 to 30 s and was followed by washing the samples by immersion in distilled water. Finally, the sample was dipped in an accelerating solution consisting of 10% HCl. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAfter nucleation, a non-commercial autocatalytic solution of electroless Ni-P, reported by Flacker \u003cem\u003eet al\u003c/em\u003e.\u003csup\u003e\u003cspan lang=\"DE\"\u003e15\u003c/span\u003e\u003c/sup\u003e was used. The deposition was performed at 50\u003csup\u003e\u0026nbsp;\u003c/sup\u003e\u0026deg;C, at a controlled pH of 5-5.3 by addition of NaOH and mechanical agitation. Table 1 shows the reagents, concentration and conditions of the solution used for electroless Ni-P deposition on polyimide surface.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Ni-P bath composition.\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eCompound\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003eConcentration / (g L\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eNiCl\u003csub\u003e2.\u0026nbsp;\u003c/sub\u003e6H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eNaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e.H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eCH\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eOONa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003eNH\u003csub\u003e4\u003c/sub\u003eCl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 132px;\"\u003e\n \u003cp\u003ePb(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 170px;\"\u003e\n \u003cp\u003e0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003ch2\u003eCharacterization\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThe following techniques and equipment were used to characterize the polyimide surfaces: contact angle OCA 15 plus (Dataphysics Instrument GmbH Filderstadt, Germany); infrared spectra (FTIR) Spectrum 100 (PerkinElmer) range 4000-550 cm\u003csup\u003e-1\u003c/sup\u003e; X-ray photoelectron spectroscopy (XPS) measurements were carried out on a Thermo Scientific K-Alpha spectrometer (Brno, Czech Republic) equipped with monochromatized Al-Ka radiation (1486 eV). Binding energies for all peaks were calibrated by the C 1s peak at 284.8 eV. The background in high resolution spectra was computed by the Shirley method. The high-resolution XPS spectra were deconvoluted using a weighted sum of Lorentzian and Gaussian components curves. The XPS data were analyzed using CasaXPS software (Casa Software, Ltd., UK, version 2.3 25PR1.0). Samples thicknesses were estimated with a Dektak XT scan profiler (Bruker, Billerica, USA). X-ray diffraction (XRD) was performed with a Shimadzu LabX XRD-6000 on an operating voltage of 40 kV with a current of 30 mA and Cu K\u0026alpha; radiation (1.5406 \u0026Aring;), with 2\u0026theta; from 10 to 80\u0026deg;. Scanning electron microscopy images and energy dispersive spectroscopy (EDS) data were obtained with a field emission gun scanning electron microscope (SEM-FEG) (MIRA 3 XMU model, TESCAN, Brno, Czech Republic) coupled with Bruker Quantax System EDS. The sheet Resistance values of the substrate were estimated at using four-point probe (Thin Film Devices, INC, FPP-2000).\u0026nbsp;\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003eFlexible polyimide substrates are of great interested of the microelectronics field, since this material can be used as substrate for the assembly of flexible electronic devices.\u003csup\u003e\u003cspan lang=\"DE\"\u003e19\u003c/span\u003e\u003c/sup\u003e This material also has an excellent thermal stability from -273 \u0026deg;C up to 400 \u0026deg;C and good dielectric properties.\u003csup\u003e\u003cspan lang=\"DE\"\u003e20\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eIn this work, the proposed pretreatment process before plating the polyimide involving three stages: (\u003cem\u003ei\u003c/em\u003e) formation of polar functional groups. This step adds new functions on the surface to enable the next step: the pretreatment is necessary because electroless deposition onto insulator materials demands the formation of seeds onto the surface. (\u003cem\u003eii\u003c/em\u003e) Nucleation (catalyzing and reducing). In this step, a redox reaction takes place between Pd\u003csup\u003e2+\u003c/sup\u003e and Sn\u003csup\u003e2+\u003c/sup\u003e on the substrate where Pd\u003csup\u003e2+\u003c/sup\u003e is reduced to Pd\u003csup\u003e0\u003c/sup\u003e to catalyze the following steps:\u003csup\u003e\u003cspan lang=\"DE\"\u003e21\u003c/span\u003e\u003c/sup\u003e,\u003cspan lang=\"DE\"\u003e22\u003c/span\u003e,\u003cspan lang=\"DE\"\u003e15\u003c/span\u003e,\u003cspan lang=\"DE\"\u003e23\u003c/span\u003eWith this, the Pd/Sn sites created on the pretreatment leads to the formation of the Pd seeds, which will enable the nucleation and growth of \u0026nbsp;NiP particles during the ED process. (\u003cem\u003eiii\u003c/em\u003e) acceleration process, where the excess of ionic tin from colloid-covered surface, which surrounds the palladium catalyst, is removed.\u003csup\u003e\u003cspan lang=\"DE\"\u003e24\u003c/span\u003e\u003c/sup\u003e,\u003cspan lang=\"DE\"\u003e16\u003c/span\u003e(\u003cem\u003eiv\u003c/em\u003e) ED process, using a Ni-P containing bath. Figure 1a shows the scheme of the polyimide reaction after the pretreatment and deposition of the metallic film through the wet process (acceleration process is not represented in this Figure because it only removes the excess Sn). Figure 1b shows a photography sequence of the ED process.\u003c/p\u003e\n\u003cp\u003eMechanistically, it has been proposed that the funcionalization step leads to the introduction of OH\u003csup\u003e-\u003c/sup\u003e groups in the surface of polyimide, which would then work as sites for attachment of Pd\u003csup\u003e2+\u003c/sup\u003e ions. After the reducing step, Pd\u003csup\u003e0\u003c/sup\u003e would be generated, which would act as seed layer for Ni-P deposition.\u003csup\u003e25\u003c/sup\u003e Then, once the seed layer has been formed, metallic Ni is deposited during ED process according to equation 1, while elemental phosphorus is co-deposited according to equation 2. Other byproducts such as hydrogen gas are also produced, as shown in equation 3.\u003csup\u003e\u003cspan lang=\"DE\"\u003e25\u003c/span\u003e\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cimg 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\" width=\"808\" height=\"189\"\u003e\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eSince the pretreatment was observed to be crucial to enable successful ED of Ni-P onto the polyimide substrate, a detailed characterization of the substrate surface before and after pretreatment was performed, as discussed below.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eCharacterization of the polyimide substrate after surface pretreatment\u003c/h2\u003e\n\u003cp\u003eFTIR spectra of the polyimide\u0026nbsp;surface before and after treatment with NaOH are shown in Figure 2.\u0026nbsp;The characteristic absorption bands of untreated polyimide surface were assigned to N-H stretch (3481 cm\u003csup\u003e-1\u003c/sup\u003e) of amine groups; C-H in aromatic stretch (3100-3000 cm\u003csup\u003e-1\u003c/sup\u003e); asymmetrical and symmetrical C=O stretch (1780 and 1708 cm\u003csup\u003e-1\u003c/sup\u003e), -NH\u003csub\u003e2\u003c/sub\u003e deformation bending (1604 cm\u003csup\u003e-1\u003c/sup\u003e), aromatic ring C=C bending (1500 cm\u003csup\u003e-1\u003c/sup\u003e), and C-N imide group (1373 cm\u003csup\u003e-1\u003c/sup\u003e).\u003csup\u003e\u003cspan lang=\"DE\"\u003e26\u003c/span\u003e\u003c/sup\u003e The polyimide surface was pretreated with NaOH solution to enhance the wettability and the concentration of polar functional groups (e.g., -OH group). As seen from the FTIR spectrum of polyimide substrates treated with NaOH solution (4 min at 25, 30, 40, 50, and 60 \u0026deg;C), the absorption bands assigned to O-H stretching bands (3700-3100 cm\u003csup\u003e-1\u003c/sup\u003e) increase with increasing surface treatment temperature. It indicates that the pretreatment with NaOH solution introduced oxygen-containing functional groups on the polyimide surface. We verified experimentally that this would then affect the adherence of the Ni-P film, with best results obtained in the 30-40 \u0026deg;C range (determined by simple 3M Scotch Tape adhesion tests). When the pretreatment was performed at 25 \u0026deg;C, the Ni-P film deposited in the subsequent steps was not uniform (flaws were observed, suggesting an incomplete substrate coverage). On the other hand, when higher temperatures (50-60 \u0026ordm;C) were used in this step, the Ni-P film would adhere very poorly on the\u0026nbsp;polyimide\u0026nbsp;surface. This behavior was thus correlated to the increase in the amide C=O content on the polyimide surface after functionalization using higher temperatures (see the signal at 1650 cm\u003csup\u003e‑1\u003c/sup\u003e), which seems to interact poorly with the metal elements, this leading to poorer adhesion.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eXPS technique was also used to investigate the chemical composition of the polyimide surface, before and after treatment with NaOH solution (4 min at 30 \u0026deg;C). Survey XPS spectrum (see Figure 3a) of the pristine polyimide sample consists of C (80.7%), O (14.2%), and N (5.5%). Typical high-resolution XPS spectra of carbon (C 1s) and oxygen (O 1s) atomic core levels are presented in Figures 3b and 3c. High-resolution C 1s XPS spectrum of the pristine polyimide substrate was deconvoluted into four main peaks assigned to C-C (53.7%), C-N (28.5%), C-O (7.4%), and C=O (10.4%) bonding, respectively. High-resolution O 1s XPS spectrum was deconvoluted into two main peaks attributed to C=O (71.5%) and C-O (28.5%) bonding, respectively.\u003csup\u003e\u003cspan lang=\"DE\"\u003e27\u003c/span\u003e\u003c/sup\u003e,\u003cspan lang=\"DE\"\u003e28\u003c/span\u003e Figure 3d shows the survey XPS spectrum of the polyimide sample after surface treatment with NaOH solution, indicating the presence of chemical elements C (70.5%), O (20.7%), N (5.5%), and Na (3.3%). High-resolution XPS spectra of C 1s and O 1s atomic core levels of this sample are presented in the Figures 3e and 3f. The same signals observed in the Figures 3b and 3c were found for the polyimide sample with surface treatment. In the high-resolution C 1s XPS spectrum (see Figure 3e), the signals referring to C-O (14.6%) and C=O (11.9%) chemical bonds were more pronounced. In addition, a new signal localized at 535.4 eV referring to the C-OH (3.2%) chemical bond was observed in the high-resolution O 1s XPS spectrum (see Figure 3f), indicating the incorporation of hydroxyl groups on the surface of the polyimide substrate after surface treatment with NaOH solution, in agreement with FTIR data.\u003c/p\u003e\n\u003cp\u003eWater contact angle measurements were then performed to evaluate\u0026nbsp;the wettability of the polyimide surface after surface treatment with NaOH solution. Contact angle images of pristine\u003csup\u003e\u0026nbsp;\u003c/sup\u003epolyimide substrate showed that the surface before pretreatment was hydrophobic, so the drop does not spread over the surface, presenting a contact angle of ca. 69\u0026deg; (Figure 4a). After the pretreatment using an aqueous NaOH solution (4 min at 25, 30 and 40 \u0026deg;C), the contact angle reduced to approximately 25\u0026deg; and the drop greatly spread on the treated surface (Figure 4b, 4c, 4d). It indicates that the wettability on the polyimide surface increased with surface treatment with NaOH solution, due to the increased concentration of hydroxyl groups on its surface, as observed from XPS and FTIR. At 50 \u0026deg;C, the contact angle becomes larger (32\u0026deg;) this behavior can also be attributed to the formation of other functionalization groups on the polyimide surface, and this can reduce the adhesion of the Ni-P film, as observed in adhesion tests performed with an adhesive tape. The treatment at 30 \u0026deg;C resulted in the smaller contact angle (23\u0026deg; Figure 4c) and therefore this temperature was chosen for the subsequent study.\u003c/p\u003e\n\u003ch2\u003eStructural, morphological, and electrical characterization of Ni-P/ polyimide samples\u003c/h2\u003e\n\u003cp\u003eFigure 5a presents the variation of Ni-P film thickness as a function of the deposition time on the polyimide substrate pretreated with NaOH solution at 30 \u0026deg;C for 4 min. The Ni-P deposition rate was 122.1 nm min\u003csup\u003e-1\u003c/sup\u003e, as calculated from the slope of the linear regression, as shown in the inset of Figure 5. Interestingly, this deposition rate is close to that obtained using for Ni-P platting on \u0026nbsp; polyethylene terephthalate (112.2 nm min\u003csup\u003e-1\u003c/sup\u003e), as reported in our previous work\u003csup\u003e17\u003c/sup\u003e. A high deposition rate corroborates the success of the surface pretreatment applied to the polyimide.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 5b presents the variation of Ni-P film sheet resistance and its standard deviation as a function of the deposition time on the polyimide substrate. As expected, these measurements show a very fast decline in the sheet resistance value as the time of deposition rises due to the thickness enhancement, but the standard deviation also decreases, which suggests that the deposition is more uniform in longer deposition times. The polyimide substrates are naturally insulators, so the sheet resistance obtained after only 2 min of deposition is still high, about 856\u0026nbsp;W/sq. However, this value decreases exponentially upon enhancing the deposition time, reaching a value of 131\u0026nbsp;W/sq at 6 min and 69\u0026nbsp;W/sq at 10 min. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 6a displays the XRD patterns of polyimide samples, with and without surface treatment and after the electroless Ni-P process, for a 6 min deposition time. This time was fixed for further investigations because the Ni-P film thickness at this condition is around 1 \u0026micro;m, a thickness that has been used as reference by our group in metallization processes. XRD pattern of the pristine polyimide sample shows that three prominent signals can be clearly observed at 2\u0026theta;\u0026nbsp;= 14.2\u0026deg;, 21.9\u0026deg;, and 26.0\u0026deg; due to some crystallinity of the substrate.\u003csup\u003e\u003cspan lang=\"DE\"\u003e29\u003c/span\u003e\u003c/sup\u003e,\u003cspan lang=\"DE\"\u003e30\u003c/span\u003e No change in the diffractogram profile was detected after surface treatment with NaOH. The presence of the amorphous Ni-P film deposited on the polyimide surface was detected from the appearance of a broad signal ranging from 40\u0026deg; to 50\u0026deg;, in which this signal centered at 2\u0026theta; = 45\u0026deg; corresponds to Ni(111) plane.\u003csup\u003e\u003cspan lang=\"DE\"\u003e31\u003c/span\u003e\u003c/sup\u003e,\u003cspan lang=\"DE\"\u003e32\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003eFigure 6b shows the surface roughness profile measured by a profilometer for the polyimide substrates: untreated, with surface treatment, and with Ni-P film deposited by electroless process. The average surface roughness of the pristine polyimide substrate (black line) was about 42.7 nm. After surface treatment (red line), the average surface roughness decreased to 34.2 nm, indicating a slight change in the morphology on the polyimide surface. After electroless Ni-P deposition the average roughness increased to 110.9 nm, suggesting the nucleation and growth of small Ni-P grains.\u003c/p\u003e\n\u003cp\u003eThe SEM images in Figure 7a show the surface morphology of the Ni-P film deposited was uniform, with\u0026nbsp;compact spherical nano-structures, without holes and scratches, and no flaws. We observed that the growth of the film occurred in the form of agglomerates with particles sizes ranging from 380 to 780 nm (Figure 7b). The EDS analysis showed a high purity film, with a high Ni concentration (~90 at%) and about 10 at% phosphorous (see Figure 7c,d). This corresponds to approximately 94 wt% of Ni and 6 wt% of P. Other works that used NaOH pretreatment of polyimide substrates, with different procedures for the catalyzing/reducing and ED steps, using higher temperatures, obtained similar Ni-P alloys with roughly 92 wt% Ni and 8 wt% P\u003csup\u003e14\u003c/sup\u003e. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFinally, the adherence of Ni-P films on Kapton was tested via bending tests, which showed no visible cracking or film delamination (see Figure 8). From the test, we observed that the Ni-P film deposited on the flexible polyimide substrate has good mechanical stability, maintaining its integrity and adherence to the polyimide after the bending test.\u003c/p\u003e\n\u003cp\u003eThe FTIR, XPS and contact angle results confirm and demonstrate the effectiveness of the pretreatment process on the polyimide surface, and the conditions that enable the wet process electroless deposition. Thickness, XRD, SEM, EDS and 4-point probe data are also consistent with each other and demonstrate that the deposited metallic layer can be obtained in a uniform and adherent film with properties suitable for use in electronic devices.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn this study, we investigated the deposition of Ni-P thin layer on the surface of the flexible polyimide through a wet surface pretreatment using only low temperatures (30\u0026deg;C and 50\u0026deg;C), providing a low-cost alternative to other more expensive methods previously reported in the literature. This adherent layer might be used as seed for the growth of other metallic films, such as gold, aiming at electronic circuit applications, thus being a versatile method besides being fast and of low cost. The characterization of Ni-P deposited samples showed that the treatment of the flexible polyimide enables a high performance in ED, with a deposition rate of 122.1 nm min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and delivering a compact spherically-shaped nano-structured film without holes, scratches and flaws, with particles sizes ranging from 380 to 780 nm, and high purity, with 9:1 Ni:P atomic ratio. The sheet resistance of the samples decreased to 69 Ω/sq for Ni-P films deposited for 10 min. With such value, it\u0026acute;s possible to fabricate structures such as Wheatstone bridges which, combined with another materials and/or functionalization, can lead to sensors/detectors of various physical parameters, like temperature, pressure and/or moisture among others.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgments\u003c/h2\u003e\n\u003cp\u003eThe authors gratefully acknowledge PCI/CTI/CNPq (301232/2024-5 and 301216/2024-0), National Council for Scientific and Technological Development (CNPq, 409215/2023-6), S\u0026atilde;o Paulo Research Foundation (FAPESP, 2017/11986-5), Shell and Brazilian Innovation Agency (FINEP 0139/21) for scholarships and financial support. The authors also thank Dr. Jos\u0026eacute; Maria Clemente da Silva Filho for the XRD measurements and Rafael de Godoi Machado for the XPS measurement at the Center for Innovation on New Energies (CINE). Research supported by CTI-Nano, strategic laboratory from SisNano, MCTI and financed by CNPq.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eAuthor Contributions\u003c/h2\u003e\n\u003cp\u003eAlex contributed with the following roles: Conceptualization, data curation, formal analysis, investigation, methodology, project administration, resources, supervision, validation, visualization, writing \u0026ndash; original draft and writing \u0026ndash; review \u0026amp; editing. Andr\u0026eacute;ia contributed with the following roles: data curation, formal analysis, investigation, validation, visualization, and writing \u0026ndash; review \u0026amp; editing. Marcelo contributed with the following roles: data curation, formal analysis, investigation, validation, visualization, writing \u0026ndash; original draft and writing \u0026ndash; review \u0026amp; editing. Michele contributed with the following roles: data curation, formal analysis, investigation, resources, validation, visualization and writing \u0026ndash; review \u0026amp; editing. Jilian contributed with the following roles: formal analysis, funding acquisition, visualization, writing \u0026ndash; review \u0026amp; editing. Ricardo contributed with the following roles: formal analysis, funding acquisition, project administration, resources, supervision, visualization, writing \u0026ndash; review \u0026amp; editing.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eConflict of Interest Statement\u003c/h2\u003e\n\u003cp\u003eAuthors certify that they have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers\u0026rsquo; bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eData and Code Availability\u003c/h2\u003e\n\u003cp\u003eNot Applicable\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eSupplementary Information\u003c/h2\u003e\n\u003cp\u003eNot Applicable\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eEthical Approval\u003c/h2\u003e\n\u003cp\u003eNot Applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eXiang, J.; Zhou, G.; Hong, Y.; He, W.; Wang, S.; Chen, Y.; Wang, C.; Tang, Y.; Sun, Y.; Zhu, Y.; \u003cem\u003eAppl Surf Sci\u003c/em\u003e \u003cstrong\u003e2022\u003c/strong\u003e, \u003cem\u003e587\u003c/em\u003e, 152848. 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[https://doi.org/10.1039/c6ra19984d]\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":"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":"polyimide, Ni-P, electroless deposition, flexible substrate","lastPublishedDoi":"10.21203/rs.3.rs-6147604/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6147604/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe purpose of this study is to report a low-cost electroless deposition (ED) process of Ni-P thin film using wet technology on flexible polyimide substrate (Kapton\u0026reg; 300HN DuPont\u0026trade;), comprising functionalization with NaOH, nucleation with Sn and Pd and acceleration with HCl. The pretreatment performed on the polyimide surface was investigate using a contact angle system and attenuated total reflection Fourier-transform infrared spectroscopy. Structural, morphological and electrical characterization of the Ni-P film were performed by X-ray diffraction spectroscopy, stylus scan profiler, scanning electron microscopy, X-ray photoelectron spectroscopy and four-point probe measurements. The characterization showed that the treatment of the flexible polyimide enables a high performance in ED, delivering a very compact spherical nano-structured film without holes, scratches and flaws, with particle size ranging from 380 to 780 nm.\u003c/p\u003e","manuscriptTitle":"Electroless Ni-P Deposition on Flexible Polyimide Substrates with Tin-Palladium nucleation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-01 09:51:59","doi":"10.21203/rs.3.rs-6147604/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":"867bfc69-37d3-4077-8605-3b0e2d526aa6","owner":[],"postedDate":"April 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-02-09T16:06:07+00:00","versionOfRecord":{"articleIdentity":"rs-6147604","link":"https://doi.org/10.1186/s40712-025-00376-8","journal":{"identity":"journal-of-materials-science-materials-in-engineering","isVorOnly":true,"title":"Journal of Materials Science: Materials in Engineering"},"publishedOn":"2026-02-07 15:58:07","publishedOnDateReadable":"February 7th, 2026"},"versionCreatedAt":"2025-04-01 09:51:59","video":"","vorDoi":"10.1186/s40712-025-00376-8","vorDoiUrl":"https://doi.org/10.1186/s40712-025-00376-8","workflowStages":[]},"version":"v1","identity":"rs-6147604","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6147604","identity":"rs-6147604","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}