Study on PLCC Lead Free Solder Joint's Thermal Reliability Based on Shape Prediction and Response Surface Methodology

Abstract

In this paper, PLCC lead free solder joint’s thermal fatigue lifetime is analyzed by using the Response Surface Methodology, combined with solder joint’s shape prediction and finite element simulation. Three key solder joint’s process parameters, pad length, gap height and solder paste’s volume are chosen to build an orthogonal array , 25 PLCC lead free SAC305 solder joint’s models with different parameters combination are built in Surface Evolver to predict the solder joint’s shape. Then the PLCC device’s surface shape models in Surface Evolver are converted to three-dimensional finite element models by using a special method. Thermal analyses give the distribution and the change of thermal stress and strain, which show the dangerous solder joint in the whole PLCC device and position with weak thermal reliability in single solder joint. Furthermore, the PLCC solder joints’ thermal fatigue lifetime are calculated with the modified Coffin-Manson equation, and the series of thermal fatigue lifetime data are processed by the Response Surface Methodology. Regression equation between thermal fatigue lifetime and the three key factors is concluded. With the solder joint’s influencing rule on thermal fatigue lifetime and the solder joint’s process parameter combination belong to the highest thermal fatigue lifetime, assembly process of PLCC is improved and then enhance the PLCC solder joint’s reliability.