Development of thermoplastic isotropically conductive adhesive

Abstract

Isotropically conductive adhesive formulations usually include epoxy resin as the polymeric matrix. Although epoxy has superior adhesion capability, one of its drawbacks is its tendency to absorb moisture. As a result, a finite amount of water may accumulate at the interface of ICA and contact pads. Previous studies have shown that the presence of water in ICA interconnects causes contact resistance degradation at the interface by means of galvanic corrosion. In this study, an alternative thermoplastic polymeric matrix with low moisture absorption is used in isotropically conductive adhesive (ICA) formulation. Presence of residual solvent in the thermoplastic ICA interconnects increased their contact resistance values. Adhesion of the thermoplastic polymer on Cu/OSP surface was better than Sn/Pb, Sn, or Ni/Au, and that trend correlated with contact resistance stability after aging. Addition of coupling agents and plasticizer improved adhesion of the thermoplastic polymer, especially on Ni/Au surface. A blend of thermoplastic and thermosetting polymers was evaluated for ICA application, and it was shown that it is a feasible approach for improving contact resistance stability.