Improvement of mechanical impact resistance of BGA packages with Pb-free solder bumps

In portable electronics or during the transport of other electronics, shock impact like drop is not easy to be avoided. Therefore, the ability of electronic packages and assemblies to resist the sudden shock impact is becoming a growing concern. Recently, some outer balls of lead free BGA packages even ´ tended to come off almost spontaneously during handling/transportation and the failures have typically a brittle nature. To overcome this, some efforts were done to improve the solder interconnects robustness to resist the shock. In this paper, a high-speed shear test is carried out to evaluate the robustness of lead-free solder interconnects of BGA packages under a shock impact. Five Pb-free solder compositions of SAC405, SAC305 + NiGe, CASTIN, and SACX are evaluated with eutectic SnPb as a reference. All BGA packages in the tests are with NiAu finished substrates. It is found that interconnects with reduced silver and copper content (SAC 101) outperform interconnects with other Pb-free solder alloys in the high-speed shear test. From the alloys studied, only BGA packages with SAC101 don´t show any brittle failure in the IMC interface similar to packages assembled with eutectic SnPb. A JEDEC based board level drop test is also carried to see the shock impact resistance of SAC101 with SAC305 and SnPbAg as references. In the drop test, the number of drops to failure for packages with SAC101 is also higher than those with SAC 305 and it is similar to the number with eutectic SnPb solder balls. It also shows that packages with Cu-OSP finished substrates outperform those with NiAu finished substrates.