Modern test methods for a comprehensive thermo-mechanical deformation analysis in area-array-assemblies

The reliability of interconnects on area-array assemblies like micro-BGA or QFN packages is strongly affected by the thermo-mechanical deformation of solder bumps as a consequence of the CTE-mismatch problem. The common approach to determine the stresses and strains for reliability predictions in the critical interconnections is the utilization of finite elements simulations of the assembly. The computation results should be verified by a combination of experiments in order to prevent systematic errors and to improve the results qualitatively and quantitatively. In this work, the potential of modern test methods for the thermal-mechanical analysis of CSPs and ball grid array packages was evaluated and demonstrated. The applied test methods were electronic- speckle-pattern-interferometry (ESPI) and a silicon test chip with multi-axial resistive structures. It became evident, that a single analysis method is not sufficient to verify all of the information derived from simulations, but that several tests have to be combined in order to account for package effects as well as for solder joint phenomena.