AN APPROACH TO DETERMINING RESIDUAL STRAINS AND MOISTURE DIFFUSION COEFFICIENTS OF CURED ADHESIVES IN ELECTRONIC PACKAGING

摘要

Polymeric adhesives are popular in the application to electronic or optoelectronic packaging for die attaching, underfilling or interconnection. Their residual strains or stresses (induced by temperature, moisture, and curing shrinkage) and moisture diffusion coefficients have to be determined and cooperated into the package design for better reliability. The purpose of this study is to propose an approach for quantifying adhesive moisture diffusion coefficients and residual strains due to chemical shrinkage, stress relaxation and temperature- and moisture-loading. This approach feature testing fully-cured adhesive/silicon bi-material plates under thermal and moisture loading using Twyman-Green (T/G) interferometry system plus analyses with Timoshenko's bi-material theory and finite element method (FEM). Three types of adhesives: paste adhesive, film adhesives A and B have been tested for illustrating the approach. The results suggest that the residual strains for the paste adhesive are only induced by CTE mismatch during thermal loading, rather than other factors, after the cured paste adhesive being cooled down to room temperature. On the other hand, the film adhesive A was found to have the additional residual strain caused by chemical shrinkage plus stress relaxation, besides thermal one, is about 2.26×10~3, which accounts for 85% of thermal strains, after the bi-material plate being cooled down to room temperature. Through moisture diffusion test, the average of the coefficients of moisture diffusion and saturated hygro-strains of the film adhesive B under 30°C/85%RH are obtained to be 1.09 ×10~6 mm2/s and 1.51 ×10~3, respectively. From the aforementioned results, it has been demonstrated that this method with a combination of experimental data and analytical tools can be able to determine the residual strains and moisture diffusion coefficients of the cured film or paste adhesives.