New high conductivity lead (Pb)-free conducting adhesives

Abstract

Solder interconnection technology is currently in need of alternatives to address environmental issues associated with lead (Pb) abatement, and elimination of fluxes and flux cleaning solvents, and technical challenges related to extending to line pitch assembly. Electrically conducting adhesive technology is one of the alternatives being actively considered in this context. The most common conductive adhesive used today is an epoxy resin filled with fine silver particles. Silver particles provide electrical conduction, while epoxy provides adhesive bonding of the components to a substrate. This material has several limitations such as low electrical conductivity, low joint strength, increase in contact resistance upon thermal cycling, and silver migration. In order to overcome these limitations, a new formulation is proposed based on alternative Pb-free conducting filler powders and tailored polymer resins. This new material provides a metallurgical bonding as well as polymer adhesive bonding leading to an increase in joint strength and in electrical conductivity. Several potential applications of these adhesive materials such as glass-to-board connection in LCD packaging, SMT package assembly to PCB, and direct chip attachment to a high density card are discussed.