Thermomechanical FEM Analysis of Sn-Bi Solder Joint During Temperature Cycling for Fine Pitch 1st Level Interconnect

Thermomechanical analysis by finite element method (FEM) was performed for Sn-Bi and Sn-Ag-Cu (SAC) solder joints with pitches of 130 microns and 40 microns in a 2D package during a temperature cycling (TC) test. The results showed a smaller inelastic strain range of solder for the Sn-Bi joints than the SAC joints. Inelastic strain ranges for Sn-Bi and SAC increase when the joint size decreases from the C4 to the Cu pillar. However, the increasing rate for Sn-Bi is remarkably smaller than that for SAC.