Sintered Micro-Silver Paste Doped with Indium for Die Attachment Applications of Power ICs

Over the past decades, the demands for high temperature power electronics for automotive applications increased continuously. Inverters and converters in power integrated circuit modules dominate both energy conversion efficiency and performance in electric vehicles. Furthermore, the operating temperature of wide band gap semiconductors like SiC and GaN are much greater than Si-based power ICs. However, conventional tin-based solders which melt at around 220°C will encounter failure problem at such high temperature. As a result, nano-silver paste and nano-copper paste were both developed to apply in die attachment as new and promising packaging materials. Nevertheless, joints of sintered pure nano-silver paste were inevitable to several problems such as copper substrate oxidation problem at high temperature and tarnishing phenomenon by sulfur and hydrogen sulfide. In addition, nano-silver particles are not only expensive to produce, but also harmful to human body because they can penetrate skins directly. Therefore, it is necessary to figure out solutions to handle the problems in pure sintered silver joints and investigate the bonding of sintered micro-silver particles to observe if the scale effect will cause negative influences to the joint.In our research, silver paste which is composed of micro-scale particles is utilized for die attachment technology with indium. As-bonded silver-indium joint can be obtained through the sintering and transient liquid phase bonding process. By adding indium element, the target is to solve the serious copper substrate oxidation problem at 300°C thermal aging and tarnishing phenomenon in sulfur-containing environment in order to enhance the mechanical reliability at high temperature. Also, mechanical property of Ag-In joints was better than that of pure sintered silver joint from results of die shear tests. Besides, thermal aging tests were conducted to investigate the phase transformation of sintered micro-silver joints and sintered silver-indium joints. Meanwhile, these samples were also put in the sulfur-containing surroundings to observe if the sulfur element will lead to failure problem in the joints. It was concluded that joints of silver-indium intermetallic compounds and solid solution phase exhibited good mechanical property, anti-oxidation property, anti-tarnishing ability, and consequently improved the problems existing in the pure sintered silver joint.