Numerical simulation on soldered joints of QFP device with different substrate materials and thicknesses

Visco-plastic finite element method was used to analyze the reliability on soldered joints of QFP devices with three kinds of different substrate materials.The results indicate that the maximum stress of soldered joint concentrates on the sharp corner of interior part of the joint with FR-4 substrate, and the maximum stress focuses on the sharp corner of exterior part of the joint with LTCC substrate and the largest stress concentrated area is at the sharp corner between the soldered joint and lead with PTFE substrate.Comparing the residual stress of soldered joints with the three substrate materials, the value of residual stress in the joint with FR-4 substrate is the least, and the value is middle in the soldered joint with PTFE substrate, and the value is the largest in the soldered joint with LTCC substrate.The analysis results of Sn37Pb soldered joints are in accord with those of Sn3.8Ag0.7Cu soldered joint.At the same time, the optimizing simulations on substrate thicknesses are made and the results show that the value of residual stress is the largest in the soldered joint when the thickness is 0.8 mm