The Effect of the Volume Fraction of Silver on the Thermal Resistance of Die Attach Adhesives

Abstract

A theory for the thermal resistance in adhesive joints between semiconductor dice and substrates has been developed. The theory takes into account the thermomechanical shear stress in the bond layer caused by differences in thermal expansion. The theoretical result indicates that only small reductions in thermal resistance can be obtained by increasing the bulk thermal conductivity of the adhesive by filling it with silver particles. Experiments were carried out in order to verify this effect. An epoxy resin was loaded with various amounts of silver particles and used to bond thermal test chips to copper substrates. There was a surprisingly small difference in thermal resistance between the various adhesives. The difference was considerably less than the difference in bulk thermal conductivity indicated, thus confirming the basic result of the theory.