Stress Analysis and Optimization of BGA Solder Joints Under Thermal Fatigue Loading by Solder Joint Structural Parameters

Abstract

BGA solder joints with 63Sn37Pb brazing material are used as an example. The thermal stress analysis of the solder joint under thermal cycling conditions is studied under changing BGA solder joint structure parameters, and optimization of the BGA solder joint structure under thermal cycling conditions is carried out. By observing a large number of research-based settings, I found that there are many factors that affect the thermal environmental conditions of BGA packaging, but this experiment only selected a relatively large impact of factors, namely, the study of BGA solder joint height, solder joint diameter, pad diameter three factors on the thermal stress analysis, the selection of solder joint diameter in order: 0.60mm, 0.62mm, 0.64mm, solder joint height in order: 0.44 mm, 0.46 mm, 0.48 mm, pad diameter: 0.48 mm, 0.50 mm, 0.52 mm. Through free combination we got 27 groups of tests, and in order to simplify the difficulty of the test, we designed this test again by using the orthogonal test method of the orthogonal test design assistant, and finally got the most representative 9 groups of test groups. We build Ansys model for each group of its test and mesh the BGA solder joint model, apply thermal fatigue, and then analyze the maximum stress of each group, and process the test data by using the extreme difference analysis method of SPSSAU software to obtain the extreme difference values of each data: 1.233, 1.367, and 0.266. At the same time, we found that the magnitude of structural factors affecting the stress of BGA solder joints under thermal fatigue conditions is in the following order: solder joint height > solder joint diameter > pad diameter, and obtained the optimal combination of test for solder joint diameter 0.60 mm, solder joint height 0.48 mm, pad diameter 0.52 mm, and the maximum thermal stress of 46.0 MPa for this model. And also when we observed the stress distribution diagram, we found that under temperature cycling (-55~125°C), BGA solder joints with different structural parameters have higher thermal stress around the top of the solder joint, in which case the first failure site is usually the top of the solder joint.