Enhancing solder joint fatigue life for ball grid array packages

Solder joint fatigue failure is quite common in plastic ball grid array (BGA) packages. Accurately predicting solder joint fatigue life and developing advanced, efficient techniques of enhancing solder joint reliability are essential to package development. In this paper, a finite element model is created to simulate the thermal-mechanical behavior of solder joints in the thermal cycling environment. Darveaux's physical model is employed to study solder joint fatigue failure caused by crack initiation and propagation. Environmental tests are also conducted and agree with the simulation results. In an effort to improve the margin of solder joint fatigue life by enhancing solder joint reliability, two alternatives to conventional eutectic solder balls are explored: 1) solder balls with interior polymer cores; and 2) solder balls with circumferential polymer collars. Finite element simulations are performed on each to verify the effectiveness of these special solder balls. The results show that solder joint fatigue life can be significantly improved. Mechanical samples are built using these two ball enhancements, and shear and environmental tests conducted on them corroborate the simulation predictions.