Reliability analysis of a SLIM/SHOCC package

In this work, a five-layer electronic package called SLIM/SHOCC is considered for thermal stress analysis using finite element method. The objective is to choose optimum materials in the 2(nd) and 3(rd) layer from the top so that the package survives due to thermal stresses. In the analysis, the materials in the top layer (Silicon), 2nd layer (95 Pb-5Sn), 4(th) layer, which is a Ball Grid Array (BGA) without underfill (eutectic 37 Pb-63Sn), and the 5(th) layer (FR4), are considered to be same in all the analyses. Different materials are considered for underfill in the 2nd layer and substrate in the 3rd layer for survival of the package. A finite element model, UASTRESS [1] is used to analyze stress for this system. This assembly is subjected to a temperature change of around 200 degreesC. Three-dimensional linear elastic and viscoplastic analyses are done to investigate reliability. Among the materials used for the substrate, 85NT and liquid crystal polymer (LCP) are the optimum ones. In addition to the substrate optimization, the effect of underfill materials on the critical stress is also considered. Results from inelastic analysis shown that the SLIM/SHOCC package may survive. The effect of considering elastic, viscoplastic and creep on critical stresses are compared in the elastic and viscoplastic analysis. The computer modeling issues are discussed in detail.