Low-temperature sintering behavior of ternary solder and copper powder for high-power device packaging

Abstract

For a high-power device of hybrid electrical vehicles requiring high thermal reliability, the concept of low temperature sintering material composed of Ag coated Cu, Sn/Ag/Cu ternary solder and chemical components removing oxide on the surface of metal fillers was studied under a processing temperature of 240oC. Due to the limited thermal reliability of conventional Tin based solder systems, the high-power device applications with a good thermal performance have been hindered because these solder materials were possibly re-melted under extreme operating conditions. Isotropic conductive paste based on thermosetting resin was previously investigated. With increase of temperature during processing, the Sn/Ag/Cu ternary solder in low temperature sintering material was melted at the melting temperature (220oC) of solder, and then, Sn was reacted with the adjacent Cu particles, producing intermetallic compound such as Cu6Sn5 or Cu3Sn. The metallic reaction between Tin and copper increased the melting temperature of the yielded metal filler from 220oC to 360oC. Therefore, we expect the enhanced reliability and thermal stability of low temperature sintering material, compared to the solder-based conventional conductive interconnection materials, because the created metal filler product (intermetallic compound) in low temperature sintering material after processing will not be re-melted at the similar operating temperature to the processing temperature, 240oC. After sintering processing of low temperature sintering material in present research, 3.7 wt.% of the residue chemicals was detected by TGA because most of chemical components was evaporated during sintering process. In conclusion, low temperature sintering material is believed to be a good candidate material for the high-power device packaging due to the phenomena of the increased melting temperature of metal filler.