Estimation of thermo-mechanical Anand model parameters of die-attach materials for power electronics assemblies

Abstract:
This work presents a general framework to identify the viscoplastic Anand model parameters for die-attach materials through the use of common instrumentation available in power electronics packaging laboratories. The method relies on the extraction of force-displacement curves from test vehicles at different temperatures and displacement rates, using a standard die-shear equipment as a substitute of specific tensile stress-test systems. The force-displacement data is then transformed to stress-strain format and post-processed to identify the Anand model parameters. For evidencing the suitability of the proposed estimation method for materials with remarkable plastic and creep behaviour, the methodology has been applied to the 95.5Pb2Sn2.5Ag solder alloy. The whole approach has been validated by comparing experimental warpage data of a test vehicle subject to thermal stresses and its simulated counterpart using the identified Anand model parameters. The fit between experiment and simulation is excellent, even predicting permanent deformations at the end of the thermal cycle.