In Situ Evaluation of Residual Stresses in an Organic Die-Attach Adhesive

Abstract

Development of the residual stresses in an organic adhesive, alumina filled epoxy (EPO-TEK H65-175MP) during curing process has been studied in-situ. The effect of the adhesive’s thickness was evaluated by preparing samples and analyzing residual stresses. Samples were prepared by applying a layer of the epoxy in various thicknesses on the back side of the silicon die. The topology changes of the die’s surface during curing process and cooling of the epoxy were monitored by digital image analysis enhanced moiré interferometry (DIAEMI). Residual stresses were calculated from the curvature changes of the surface of the die. The results show that the stress buildup is mainly caused by the mismatch in coefficient of thermal expansion between the adhesive and the die. Relaxation of the residual stress was found while the samples were kept in an open environment at room temperature. Such reduction in stress may be attributed to moisture absorption by the epoxy that results in expansion of the epoxy.