Development of low cost, low temperature conductive adhesives

Electrically and/or thermally conductive materials comprising metallic filler particles and polymer matrix have been actively investigated as replacements for the solder interconnections used in microelectronic applications. Silver-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 as a replacement for solder interconnections, such as low electrical conductivity, low joint strength, increase in contact resistance upon thermal cycling, lack of reworkability, and silver migration. In order to overcome these limitations, a new formulation has been developed based on alternative high conducting filler particles and tailored polymer resins. The high conducting filler particles are coated with low melting point, non-toxic metals or alloys which can be fused to achieve metallurgical bonding between adjacent particles as well as particles to the substrate contacts. Specifically, an electrically conductive adhesive made of Sn-coated Cu powder and polyimide-siloxane resin was developed, and their salient properties were reported previously. This material is a good candidate for the high temperature solder joints such as controlled collapse chip connection (C4) and solder ball connection (SEC) to a ceramic substrate, but not for the polymeric printed circuit board applications.