Stress Analysis of Thermal Inclusions With Interior Voids and Cracks

Abstract

Thermal mismatch induced residual stresses are identified as one of the major causes of voiding and failure of some critical components in electronic packaging, such as passivated interconnect lines and isolation trenches. In this paper, a general method is presented for thermal stress analysis of an embedded structural element in the presence of internal or nearby voids and cracks. Here, the elastic mismatch between dissimilar materials is ignored. Hence, the embedded structural element is modeled as a thermal inclusion of arbitrary shape surrounded by an infinite elastic medium of the same elastic constants. Thermal stresses are caused by thermal mismatch between the inclusion and the surrounding material due to a uniform change in temperature. With the present method, the problem is reduced to one of an infinite homogeneous medium containing the same voids and cracks, subjected to a set of remote stresses determined by the geometrical shape of the thermal inclusion. In particular, the remote stresses are uniform when the thermal inclusion is an ellipse. The method gives an elementary expression for the internal stress field of a thermal inclusion with a single interior void or crack. Several examples of practical interest are used to illustrate the method. The results show that an internal void or crack can significantly change stress distribution within the inclusion and gives rise to stress concentration around the void or crack. [S1043-7398(00)00303-0]