基板材料对QFP焊点应力应变影响的数值模拟

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

采用粘塑性有限元法,针对三种不同基板材料,对Sn3.8Ag0.7Cu焊点的应力及应变进行分析。结果表明,FR-4基板对应焊点的最大应力集中在焊点最内侧的尖角处;LTCC基板对应焊点的最大应力集中在焊点最外侧的尖角处;PTFE基板对应焊点的最大应力集中在焊点和引线交界的尖角处。三种基板材料中,FR-4基板对应焊点的残余应力最小,LTCC基板对应焊点残余应力最大,PTFE基板对应焊点居中。运用Anand方程计算得出Sn37Pb钎料的分析结果和Sn3.8Ag0.7Cu钎料对应的结果具有相同的规律。对基板厚度进行的优化模拟计算结果表明,基板厚度为0.8mm时对应焊点的残余应力最大。

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.