High Thermal Conductive Die Attach Paste Using Polymer and Micron Size Silver for Power Semiconductor Package

Abstract

Abstract Power semiconductor package manufactures and electronic device suppliers have been looking for Pb-free alternative to traditional high Pb solder die attach adhesives. Lead solders have high thermal conductivity, 30–50W/mK, and known process with some difficulties in high volume mass production such as void, bond line control, and requiring reducing atmosphere such as forming gas. Lead is now categorized as hazardous substance to human body and environment and its products are scheduled to be banned within a few years. Standard silver epoxy pastes and Electrically Conductive Adhesives (ECSs) are other forms of die attach adhesives but the thermal conductivity is not adequate for Power devices. Eutectic gold-tin solder (80Au20Sn) has 57W/mK but it is high cost material. Currently Silver sintering material has become popular for electronic device because it has high thermal conductivity (150~250W/mK) by using nano silver sintering. But it requires high bonding temperature and pressure. It makes brittle bonding structure and has limitation in die size due to high stress. New silver sintering material in this paper is composed of micron size silver and organic polymer. This technology overcomes all the limitations of conventional silver epoxy, eutectic gold thin solder and silver sintering product by using the unique design of polymer composition. This new silver sintering technology using polymer and micron size silver is a cost effective solution to replace Pb solder for power device and the thermal performance is almost same as nano silver sintering products. The application process is the same as standard silver epoxy and does not require new equipment. It is a cost effective drop in solution.