Development of low cost, low temperature conductive adhesives

Abstract

Summary form only given. Electrically and/or thermally conductive materials comprising metallic filler particles and polymer matrix are actively investigated for replacement of the solder interconnects used for microelectronic applications. Ag-filled epoxy resin materials originally developed for thermal conduction in die attach applications have been candidates for this purpose. However, several limitations have been realized when they are considered for solder interconnect replacement, such as low electrical conductivity, low joint strength, increased contact resistance upon thermal cycling, lack of reworkability, Ag migration, etc. In order to overcome these limitations, a new formulation has been developed based on alternative high conductivity filler particles and tailored polymer resins. The high conductivity filler particles are coated with low melting point nontoxic metals or alloys which can be fused to achieve metallurgical bonding between adjacent particles as well as to a substrate. Specifically, a conductive adhesive made of Sn-coated Cu powder and polyimide-siloxane resin was developed, and its salient properties were reported previously. This material is a good candidate for replacing high temperature solder joints such as controlled collapse chip connection (C4) and solder ball connection (SBC) to a ceramic substrate, but not for assembly on polymeric PCBs. In this paper, we report a new formulation of electrically conductive adhesive materials with coated metal filler, which can be used for low temperature and low cost applications.