Development of technology for deposition of thick copper layers onto ceramic substrates applied in power electronics published by Ural Federal University eISSN 2411-1414; chimicatechnoacta.ru LETTER 2022, vol. 9(3), No. 20229307 DOI: 10.15826/chimtech.2022.9.3.07 1 of 4 Development of technology for deposition of thick copper layers onto ceramic substrates applied in power electronics Yuri K. Nepochatov a, Pyotr M. Pletnev b , Vladimir F. Kosarev c, Тatiana S. Gudyma d* a: HC PJSC NEVZ–Soyuz, Novosibirsk 630049, Russia b: Department of Physics, Siberian State Transport University, Novosibirsk 630049, Russia c: Laboratory of cold gas-dynamic spraying, Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk 630090, Russia d: Department of Chemistry and Chemical Technology, Novosibirsk State Technical University, Novosibirsk 630073, Russia * Corresponding author: gudymatan@mail.ru This paper belongs to the CTFM'22 Special Issue: https://www.kaznu.kz/en/25415/page. Guest Editors: Prof. N. Uvarov and Prof. E. Aubakirov. © 2022, the Authors. This article is published in open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract The basic element of the design of a power module is a metallized ce- ramic substrate. In this work, the formation of metallization coatings by the method of thermal transfer of metallization pastes (Mo-Mn-Si + binder) for alumina and aluminum nitride ceramics was carried out. The fixing of the metallization coating on the ceramic substrate was performed by firing at a temperature of 1320 °C. The subsequent deposition of the copper layer was carried out by the method of cold gas-dynamic spraying (CGDS) followed by annealing of the deposited coating. For high-quality adhesion, the optimum annealing tempera- ture was 1000 °C. Keywords ceramics metallization coating aluminum nitride copper adhesion Received: 23.06.22 Revised: 19.07.22 Accepted: 19.07.22 Available online: 26.07.22 Key findings ● The technology of a two-layer metallization coating on ceramic substrates made of aluminum nitride and oxide was developed. ● The resulting copper coatings are characterized by a strong adhesive bond with the base and low elec- trical resistance (at the level of 3·10–6 Ohm·cm). ● For high-quality adhesion, the optimum annealing temperature was 1000 °C. 1. Introduction Cold gas dynamic spraying (CGDS) is a relatively new modification of cold spraying techniques that uses con- verging-diverging (De Laval) nozzle at a supersonic veloci- ty to accelerate different solid powders towards a sub- strate on which they are plastically deformed. This defor- mation results in adhesion to the surface. CGDS is one of the innovative cold spraying processes with fast-growing scientific interests and industrial applications in the fields of aerospace, automotive and biotechnology. Cold spray research and development efforts have doubled during the last decade and along with new industry applications and novel demands provide both a strong body of knowledge and market pull to identify and address these roadblocks. [1, 2]. Due to the high strain rate deformation of particles in (CGDS), in situ investigation is challenging. Metallurgi- cal bonding is one of the main adhesion mechanisms of particles during coating buildup [3]. The properties of the kinetically deposited coating layer are significantly affect- ed by the microstructure of the coating. The most power- ful influencing factors in microstructural evolution of ki- netic-sprayed coating layers are instant generation of thermal energy and high-strain, high-strain-rate plastic deformation at the moment of particle impact [4]. Heat treatment of the 316 L austenitic steel coating improves its mechanical properties [5]. In [6] the microstructure of the coating obtained by cold gas-dynamic spraying was inves- tigated. A Cu-Al2O3-Zn powder blend was sprayed onto a copper substrate to restore a worn copper contact wire. The coating thickness was 1–2.5 mm. Improved adhesion http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2022.9.3.07 mailto:gudymatan@mail.ru http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0003-0190-7133 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2022.9.3.07&domain=pdf&date_stamp=2022-7-26 Chimica Techno Acta 2022, vol. 9(3), No. 20229307 LETTER 2 of 4 strength was achieved through substrate surface prepro- cessing with coarse Al2O3 particles. To obtain the pattern of an electronic power module, ceramic substrates should be metallized. Therefore, con- ducting layers, over 300 µm thick, are deposited by differ- ent techniques to form multilevel metallization [7]. While in production and operation, the metallized structures of power modules are exposed to thermal and mechanical stresses. The research objective is to optimize the technique of thick copper layers deposition onto ceramic substrates used in power electronics. We considered the use of finely-dispersed PMVD-0, PMVD-1 and coarse PMС-1 copper powders for their sput- tering by gas dynamic cold spray technique (GDCS). After preliminary experimental studies of gas dy- namic cold spray technique (GDCS), we made a choice of PMС-1 copper powder (GOST 4960-2009) as the most appropriate, affordable and cheap. The basic element of the power module structure is considered to be a metallized ceramic substrate with the power semiconductor crystal, which is used for imple- menting two main functions: firstly, for electrical isola- tion of conductor buses patterned on one or both sides; secondly, for the conductance of heat emitted by the ac- tive elements of the electronic power module to heat ra- diators. Besides their high heat conductivity, the sub- strates of power modules must be very strong, heat- and chemically resistant. In this regard, we use the sub- strates made from different grades of aluminum oxide ceramics and aluminum nitride ceramics providing high dissipation capacity. Based on the properties analysis carried out for ceramic materials applied by DBC tech- nology abroad [8, 9], we come to the conclusion that aluminum oxide ceramics with the content of aluminum oxide exceeding 95% is more frequently used, but alumi- num-nitride ceramics with the content of nitride oxide, which is more than 98%, is suitable for the circuits with high specific dissipation capacity. Taking into account their main characteristics, aluminum-oxide ceramic sub- strates for DBC boards made by СЕТС (China) are compa- rable with ВК96 substrates produced by JSC NEVZ- Ceramics (Russia). However, their characteristics are inferior to the ones of ВК100 ceramics produced by JSC NEVZ-Ceramics (Russia), where the content of the basic substance is equal to 99.7% (in contrast to VК-96 ceram- ics with 96% content of the base material). With regard to their physical properties, aluminum- nitride ceramics (AlN) is characterized by high thermal conductivity (170–200 W/m·К) and electrical resistance stability (1013–1014 Ohm·cm) when the temperature is increasing [10–13]. In Russia JSC NEVZ-Ceramics special- izes in manufacture of aluminum-nitride ceramic sub- strates [9]. Produced at this enterprise, aluminum- nitride substrates are characterized by high thermal con- ductivity of 160–185 W/m·К, isolation and strength pa- rameters at the level of world’s brands, such as MARUVA (Japan), LEATEC (Taiwan), ClecGroup (China), CeramTec (Germany). The substrates are produced by slip casting tech- nique followed by annealing of aluminum-oxide ceram- ics at 1650 °С and aluminum-nitride ceramics at 1850 °С. 2. Experimental Metallized coatings (MC) formation was tested by the heat transfer of two metallization pastes compositions for alu- minum-oxide and aluminum-nitride ceramics. Pastes compositions: А. Mo-Mn-Si+Ta2O5+ZrO2+TiH2+binder. B. Mo-Mn-Si+ binder. The organic binder for the metallization pastes con- tains: ethylcellulose-100, α-terpineol, dibutylphthalate and oleic aсid. Surface preparation is considered to be one of the main stages of metallized coating formation on ceramics. Ce- ramic substrates had been mechanically polished before metallization to obtain alignment and surface roughness of Ra = 0.15 µm. MC bonding on the ceramic substrates was achieved via its annealing. In this regard, nitrogen-hydrogen through- and pusher-type furnaces were used. The furnac- es consist of 5 mullite muffles, which are 90 cm long. The muffles are located in series to provide a continuous channel with 3 temperature ranges. Annealing was carried out with 30 minutes exposure at 1320 °С. The GDCS technique is based on acceleration of 1–150 µm particles with a supersonic gas flow up to the speed of 500–1200 m/s. The particles colliding with an obstacle tend to bond on it without melting [14, 15]. Meanwhile, the substrates are not strongly affected by temperatures. Sputtering was carried out on VK-96 aluminum oxide substrates with the dimensions of 30290.3 mm, and with a Mo-Mn-Si sublayer being 10–20 μm thick. PМС-1 copper powder was used for sputtering. Formation of metallized coatings from copper pow- ders was carried out according to typical GDCS diagrams with the use of a planar contracting-expanding nozzle with 3.053.05 mm critical cross section and 9.53.05 mm exit geometry. The rate of powder con- sumption from a dispenser was set to 0.1 g/s. The dis- tance of sputtering was equal to 30 mm; the nozzle scan- ning velocity against the substrate varied from 5 to 50 mm/sec. Air was chosen as a carrier and working gas. The deposition was conducted on the GDCS ITAM SB RAS test installation. The substrates were split into two batches after sputtering. Then annealing was carried out in the hydrogen medium at different temperatures to determine the optimal thermal mode. Chimica Techno Acta 2022, vol. 9(3), No. 20229307 LETTER 3 of 4 3. Results and discussion Since the products obtained are operated in air, the re- sistance of the coatings in aggressive media (acids or base solutions) was not determined. It is also known that semiconductor devices with these products are operated at low temperatures (not exceeding 125 °C). For this rea- son, the thermal stability of coatings was not studied. The most important performance characteristics of coat- ings are adhesion resistance and low electrical resistivity. The key parameters were determined after annealing as follows: the measured values of adhesion and intrinsic resistance were compared with the same parameters for DBC-substrates produced in Germany and China (Table 1). 1000 °С appeared to be the optimum annealing tempera- ture for adhesion. The best results are peculiar to DBC- substrates with the lowest resistance, which is close to the resistance of pure copper. The substrates with thick cop- per layers sputtered by the GDCS technique are character- ized by the key parameters close to the values of DBC- substrates, despite the use of copper powder to obtain the copper coatings. 4. Conclusions The technology of applying a two-layer metallization coat- ing on ceramic substrates made of nitride and aluminum oxide was developed. Initially, a layer of molybdenum- manganese-silicon was deposited on the surface of the substrates by burning in a nitrogen-hydrogen medium for 30 minutes at a temperature of 1320 °C. At the second stage, a layer of copper was deposited by the CGDS meth- od with a flat Laval nozzle. The working gas was air. After deposition, annealing was carried out in hydrogen atmos- phere. The optimal annealing temperature was 1000 °C. The obtained coatings are characterized by a stable adhe- sive bond of the copper coating with the base (the adhe- sion value exceeds 60 MPa) and low electrical resistance (at the level of 3·10–6 Ohm·cm). Supplementary materials No supplementary materials are available. Funding The work was funded by the State task of Ministry of Sci- ence and Higher Education of Russia (project no. FSUN- 2020-0008). Acknowledgments None. Table 1 Measurement results of adhesion and intrinsic resistance. No. Sample Adhesion MPa Average value of intrinsic resistance ρ·106, Ohm·cm 1 GDCS, Al2O3 + MoMnSi + Cu, 850 °С 63.7 2.95 2 GDCS, Al2O3 + MoMnSi + Cu, 850 °С 51.7 3.05 3 GDCS, Al2O3 + MoMnSi + Cu, 950 °С 65.3 3.18 4 GDCS, Al2O3 + MoMnSi + Cu, 1000 °С 66.2 3.22 5 GDCS, Al2O3 + MoMnSi + Cu, 1000 °С 67.2 3.30 6 GDCS, AlN + MoMnSi + Cu, 850 °С 8.3 2.91 7 GDCS, AlN + MoMnSi + Cu, 850 °С 6.3 2.81 8 GDCS, AlN + MoMnSi + Cu, 950 °С 20.2 2.92 9 GDCS, AlN + MoMnSi + Cu, 1000 °С 31.3 3.07 10 GDCS, AlN + MoMnSi + Cu, 1000 °С 33.0 2.98 11 DBC, Al2O3 + Cu, 1065– 1080 °С (Germany) 59.0 2.40 12 DBC, Al2O3 + Cu, 1065– 1080 °С (China) 28.5 2.90 Author contributions Conceptualization: N.Yu.K. Data curation: N.Yu.K. Formal Analysis: N.Yu.K., P.P.M. Investigation: N.Yu.K., P.P.M., G.T.S. Methodology: N.Yu.K., P.P.M. Project administration: N.Yu.K. Supervision: P.P.M., G.T.S. Validation: N.Yu.K., P.P.M., K.V.S. Visualization: N.Yu.K., P.P.M. Writing – original draft: P.P.M., K.V.S. Writing – review & editing: N.Yu.K., G.T.S. Conflict of interest The authors declare no conflict of interest. Additional information Author IDs: Yuri K. Nepochatov, Scopus ID 56059064700; Pyotr M. Pletnev, Scopus ID 6603166237; Vladimir F. Kosarev, Scopus ID 7005349023; Тatiana S. Gudyma, Scopus ID 57220042373. Websites: HC PJSC NEVZ–Soyuz, https://nevz.xspe.ru; Siberian State Transport University, http://www.stu.ru; http://www.scopus.com/inward/authorDetails.url?authorID=56059064700 https://www.scopus.com/authid/detail.uri?authorId=6603166237 https://www.scopus.com/authid/detail.uri?authorId=7005349023 https://www.scopus.com/authid/detail.uri?authorId=7005349023 https://www.scopus.com/authid/detail.uri?authorId=57220042373 https://nevz.xspe.ru/ http://www.stu.ru/ Chimica Techno Acta 2022, vol. 9(3), No. 20229307 LETTER 4 of 4 Institute of Theoretical and Applied Mechanics SB RAS, http://itam.nsc.ru; Novosibirsk State Technical University, https://en.nstu.ru. References 1. 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