Numerical Analysis on Stress and Strain in QFP Lead-Free Solder with Temperature Impact

To study the relation between the QFP lead-free solder stress and strain accumulation under the condition of the impact of temperature (-55°C~125°C), Visco-plastic finite element model based upon Anand constitutive equations is established to numerically analyze the interfacial stress of solder formed by three different kinds of solders to the same substrate FR-4. The results shows that the interface stress between three different solders and FR-4 board is different, and 95.5Sn3.8Ag0.7Cu is smaller than 63Sn-37Pb, So 95.5Sn3.8Ag0.7Cu will be helpful for the connecting reliability in electronic package; After circular temperature impact, the joint's maximum stress formed by 95.5Sn3.8Ag0.7Cu usually accumulated in the middle of both sides and right chamfer; During the temperature cycle, the greatest strain X direction is compression strain.