Influence of the Hybrid BGA Residual Stress after Reflow on the Thermal Cycling Reliability

Abstract

Thermal cycle reliability in Sn3.0Ag0.5Cu lead-free solder joints of ball grid array(BGA) package assembled with eutectic SnPb paste is investigated under the residual stress induced by reflow soldering. According to the mixed BGA package, the finite element model of lead-free and mixed BGA package is established. The residual stress and strain of BGA solder bumps are obtained after loading the different reflow profiles. The peak temperature ranges from 220 ℃ to 265 ℃, while the cooling rate is from 1 ℃/s to 6 ℃/s. The thermal cycling loads are applied on the BGA package model with the 243 ℃ peak temperature and 3 ℃/s cooling rate. The solder joint lifetime is calculated based on the equation of Coffin-Manson. In the reflow analysis, the cooling rate has a greater influence to the residual stress which increases from 27.9 MPa to 32.5 MPa with the cooling rate adding, while the highest temperature in the reflow curve has obvious impact on the residual strain. In the thermal recycle analysis, the most dangerous locationis is the upper-left corner of the BGA ball as the high stress and strain. The prediction life of the hybrid BGA could be compatible to the SnPb solder joints. Compared to the reflow curve load the life prediction among them has almost no difference.