Solid State Bonding of Silver Foils to Metalized Alumina Substrates at 260°C

Summary In this study, 6 mm 6 mm Ag foils were bonded directly onalumina substrates which were precoated with TiW and Au with-out any bonding medium such as solder. This is made possible bysolid state bonding theory where Ag atoms and Au atoms arebrought within atomic distance so that they can share electrons.The close proximity of Ag and Au is achieved by deformationwith static pressure. Since Ag and Au are ductile, only 1000 psiand 260 C are required. SEM images show that the Ag foil iswell bonded to the Au layer on alumina. Five bonded sampleswent through shear test. The shear strength measured far exceedsthe strength requirement speciﬁed in MIL-STD-883G standard.This bonding technology can serve as an alternative to DBC orDBA technology on applications where Ag is preferred over Cudue to its ductility to manage CTE mismatch and Ag is preferredover Al owing to its higher thermal conductivity. References [1] Yoshino, Y., 1989, “Role of Oxygen in Bonding Copper to Alumina,” J. Am.Ceram. Soc., 72(8), pp. 1322–1327.[2] Dupont, L., Khatir, Z., Lefebvre, S., and Bontemps, S., 2006, “Effects of Metal-lization Thickness of Ceramic Substrates on the Reliability of Power Assem-blies Under High Temperature Cycling,” Microelectron. Reliab., 46(9–11), pp.1766–1771.[3] Yoshino, Y., Ohtsu, H., and Shibata, T., 1992, “Thermally Induced Failure ofCopper-Bonded Alumina Substrates for Electronic Packaging,” J. Am. Ceram.Soc., 75(12), pp. 3353–3357.[4] Schulz-Harder, J., 2001, “HPS DBC Substrates for High ReliableApplications,” Proceedings of IMAPS Nordic, Oslo, Norway.[5] Schulz-Harder, J., 1997, “Reliability of Direct Copper Bonded (DBC) Sub-strates,” Proceedings of ISHM 11th European Microelectronic Conference,Venice, Italy.[6] Schulz-Harder, J., 2003, “Advantages and New Development of Direct BondedCopper Substrates,” Microelectron. Reliab., 43(3), pp. 359–365.[7] Cusano, D. A., Loughran, J. A., and Sun, S. E., 1976, “Direct Bonding of Met-als to Ceramics and Metals,” U.S. Patent No. 3,994,430.[8] Dalgleish, B. J., Trumble, K. P., and Evans, A. G., 1989, “The Strength andFracture of Alumina Bonded With Aluminum Alloys,” Acta Metallic., 37(7),pp. 1923–1931.[9] Ning, X. S., Lin, Y., Xu, W., Peng, R., Zhou, H., and Chen, K., 2003,“Development of a Directly Bonded Aluminum=Alumina Power ElectronicSubstrate,” Mater. Sci. Eng. B, 99(1–3), pp. 479–482.[10] Knoll, H., Weidenauer, W., Ingram, P., Bennemann, S., Brand, S., and Petzold,M., 2010, “Ceramic Substrates With Aluminum Metallization for PowerApplication,” Proceedings of IEEE Electronic System-Integration TechnologyConference, Berlin, Germany, pp. 1–5.[11] Lei, T. G., Calata, J. N., Ngo, K. D. T., and Lu, G. Q., 2009, “Effects of LargeTemperature Cycling Range on Direct Bond Aluminum Substrate,” IEEETrans. Device Mater. Reliab., 9(4), pp. 563–568.[12] Lee, C. C., Wang, D. T., and Choi, W. S., 2006, “Design and Construction of aCompact Vacuum Furnace for Scientiﬁc Research,” Rev. Sci. Instrum., 77(12),p. 125104.[13] Wang, P. J., Kim, J. S., and Lee, C. C., 2008, “Direct Laminating SilverFoils on Copper Substrate,” J. Mater. Sci.: Mater. Electron., 19(11), pp.1097–1099.[14] Available online: http://www.q-tech.com/assets/tests/std883_2019.pdf