Development of high conductivity lead (Pb)-free conducting adhesives

Electrically conducting adhesive technology is one of the alternatives being actively investigated for the possibility of replacing the solder interconnection technology used for microelectronics applications. An isotropically conducting adhesive consists of metallic filler particles dispersed in the matrix of a polymer resin. Silver-filled epoxy resin is commonly used for thermal conduction in die attach applications. Silver particles can provide electrical and/or thermal conduction, while epoxy provides adhesive bonding of the components to a substrate. This material has several limitations when it is 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 is proposed based on alternative Pb-free conducting filler powder and tailored polymer resins. The conducting filler particles are coated with low melting point, nontoxic metals which can be fused to achieve metallurgical bonding between adjacent particles as well as to a substrate. This new conductive adhesive material has shown improved electrical and mechanical properties over the existing silver-filled epoxy materials.