Comparison of the thermal-mechanical behavior of a soldered stack influenced by the choice of the solder

Abstract

Thermal cycling causes deformations in electronic packaging structures, which may result in severe loads of solder connections. Prediction of stresses and strains in the solder connections is a critical step in design for the reliability of interconnected parts. Leaded soldering materials have been broadly used for electronic interconnects in the past due to their favorable electric, mechanical and thermal properties. Presently many different lead-free solder materials are applied as a suitable replacement for the hazardous eutectic SnPb solder. Lead-free solders are frequently Sn-based alloys with silver (Ag) and copper (Cu), resulting in a higher melting temperature. In an electronic package, the thermal-mechanical integrity of a soldered structure is of high importance for the reliability of the assembly. Hence, its mechanical properties and consequently mechanical behavior should be analyzed to probe the reliability of unleaded solders.In this work, a fundamental finite element model was created for an electronic assembly, on which cyclic thermal and mechanical load was applied. For the interconnecting solder, three types: Sn-3.5Ag, SAC305, and SAC387 were employed in the different models and the integrity of the package were evaluated.