A fracture mechanics analysis of the effects of material properties and geometries of components on various types of package cracks

Various package cracks observed in service, with different locations and propagation directions, in plastic packages of surface mount technology (SMT) are analyzed in terms of the energy release rate in fracture mechanics. It has been reported that the types of the cracks observed in the package depend on the chip size, relative thickness of the epoxy resin on the chip and under the chip pad, properties of the materials and the adhesion strength of the interfaces in the package. The stress derived from the thermal expansion mismatch of the materials during the temperature cycling and the pressure induced by the expansion of moisture absorbed in the package at soldering temperature are considered separately in estimating the effects of various parameters on the package cracks. As a result of the analysis, we find that the propagation direction of the package crack is dependent on the location of the delaminated interface from which the package crack originates and the loading type imposed on the package, and that the influence of the various parameters on the package cracks are largely dependent on the loading type. Some results of the analysis are compared with the experimental results.