Large-Scale Stress Analyses for Fatigue Reliability at Die-Mount Solder of Plastic IC Packages

In this paper, the influence of the interface debonding area between the molding material and the metal frame on the fatigue reliability at die-mount solder joints in plastic IC packages was studied by means of large-scale finite element analyses. There are several factors causing the interface debonding between the molding material and the metal frame, such as manufacturing process, moisture absorption and deformation under field conditions. The debonding will change the structural stiffness of the packages and deformation shape during a thermal or mechanical load. Therefore, it is a critical issue for fatigue reliability. In this paper, three-dimensional large-scale finite element analysis is used for evaluating the influence of the debonding area on fatigue reliability under thermal cycling. The die-mount solder considered is the high-temperature solder 5Sn/95Pb. which is described by the nonlinear kinematic hardening model of Armstrong and Frederick in the finite element constitutive model. From the result of stress analyses, the debonding area has a large influence on inelastic strain, which is related to fatigue reliability. Large-scale finite element analysis is capable of providing useful guidance for structural design and material selection of plastic IC packages.