Evaluation of die-attach adhesives by curvature measurements

The authors examined three types of die-attach adhesives by measuring curvatures in assemblies that are formed by adhesively joining silicon chips to alumina substrates. The adhesives differ mainly in their post-cure elastic moduli, which are 24 GPa for a solder-like adhesive, 2.7 GPa for an epoxy-like adhesive, and 0.003 GPa for a gel-like adhesive. All of the as-prepared assemblies have residual bending resulting from the adhesive curing process. The assembly bonded by the gel-like adhesive has substantially lower, about a factor of ten less, bending than the assemblies attached by the other two types of adhesives. Thermal responses of assembly curvatures are measured by subjecting the assemblies to a temperature excursion from -15°C to 160°C. The measured temperature dependences of curvature in all three types of assemblies are found to be in good agreement with the theoretical derivations by E. Suhir (1986) for thermally induced bending in finite tri-material structures