Modeling and reliability analysis of lead-free solder joints of bottom leaded plastic (BLP) package

The electronic packaging and assembly technology is developing to high-density, fine-pitch and micromation. At the same time, an ever increasing need has developed for a lead-free solder joint interconnection due to the restrictions on the use of lead, and the upward spiraling market demand of green products. As a result the reliability of solder joint has attracted a great deal of attention, especially the lead-free solder joint. In this study, the three-dimensional (3D) shape of bottom leaded plastic (BLP) solder joints are predicted by the surface evolver software tool based on the minimum energy theory. And the geometrical models for reliability analysis are built directly from 3D shape models of BLP solder joints predicted by surface evolver using interface software of model converting. The lead-free solders considered are 96.5Sn3.5Ag and 95.5Sn3.8Ag0.7Cu. The 63Sn37Pb and 62Sn36Pb2Ag leaded solders are also considered to establish baselines. The Anand unified viscoplastic constitutive law is applied to represent the viscoplastic deformation behaviors for these solder alloys. Time-temperature-dependent nonlinear analysis of BLP solder joints on printed circuit board (PCB) assemblies subjected to thermal cycling conditions are presented using ANSYS finite element simulation software tool. The stress distribution, strain distribution and failure location of BLP-I and BLP-II solder joints are presented. The comparisons of Von Mises stress time history and equivalent plastic strain time history between different solder joints are provided also. The thermal fatigue life of BLP solder joints is predicted by the modified Coffin-Manson model based on the equivalent plastic strain range. Also, the effects of various solders and solder joint shape on BLP solder joint reliability are provided