Bus Bar Solder Joint Durability Evaluation

Thermostructural analyses were conducted in support of an investigation into bus bar solder joint reliability for military aircraft. In electronics packaging applications, the most common cause of solder joint failure is repeated straining during temperature cycling as a result of mismatch of the coefficients of thermal expansion (CTE) of the solder joint assembly. To ensure that the bus bar solder joints for military aircraft have sufficient reliability to withstand the environmental exposures, a thermostructural evaluation becomes necessary. To analyze the durability of bus bar solder joints, nonlinear finite element analyses were conducted with the ABAQUS computer code. In the analysis, the solder constitutive relation was incorporated into the ABAQUS code to calculate the nonlinear strains of the solder joints during temperature cycling. These nonlinear strains, combined with modified Manson-Coffin fatigue life prediction theory and Miner’s cumulative damage law, were then used to predict the cumulative damage index (CDI) of the solder joints for two thermal cycling life times. The CDI was also estimated for the case where cracks have initiated and propagated through about half the length of the solder joint. All analysis results indicate that these solder joints have sufficient structural margins to survive two thermal cycling life times.