Thermo-mechanical reliability of SAC leadfree alloys

In this paper, thermo-mechanical reliability of four different low-silver SnAgCu (SAC) lead free alloys is investigated in a harsh thermal environment of -55 to 125°C. Four configuration of test boards were assembled all having identical 100 I/O, 0.8mm pitch chip array ball grid array (CABGA) packages. Previous researchers have demonstrated the superior performance of low-silver leadfree alloys in shock and vibration. The presented study focuses on understanding the low-silver alloys reliability and the effect of dopants for prolonged operation under thermo-mechanical stresses in harsh environments. A direct comparison has been made between the low-silver alloys with and without dopants, keeping the package architecture and board assembly construction identical amongst the board assemblies tested. Solder alloys studied include SAC105, Sn0307, SACX, and SACX+. Accelerated test data has been gathered under thermal cycling from -55 to 125°C with ten minute dwells at each extreme. Weibull distributions have been created for all four-alloys and failure modes studied with cross-sections.