Physics based prognostics of solder joints in avionics

Abstract

Applicability of a physics based prognostics approach for solder joints using microstructural damage models is investigated. A modified deformation mechanism map for the solder alloys is introduced where grain boundary sliding (GBS) plays a dominant role during creep deformation. The high homologous temperature of solder as well as the combined thermal-vibration cycling experienced during typical operating missions necessitates the use of a combined creep-fatigue failure approach. In this work, a PCB consisting of a heat generating chip with Ball-Grid Array (BGA) solder joints is considered for avionics application. A prognostics based Life Cycle Management approach was used to perform the mission analysis, FEA, thermal-mechanical stress analysis and damage accumulation analysis. The remaining useful life (RUL) is predicted for different rupture strains. The uniqueness of this approach lies in the use of microstructure based damage models and consideration of both material and mission variability to predict the RUL under actual usage. The life critical nodes were observed near the junction of the solder joints with the substrate due to high disparities in their coefficients of thermal expansion. In addition, the probabilistic analysis was also performed by randomly varying the grain size and fitting a two-parameter Weibull distribution to the failure data. The model calibration and the results show some practical trends that need to be verified through future experimentation. The simulation results demonstrate the viability of using a physics based approach for the prognosis of solder joint failures in avionics.