X-RAY MICRO-COMPUTED TOMOGRAPHY BASED FE-MODELS TO CAPTURE REALISTIC MANUFACTURING VARIABILITY IN Cu-Al WIREBONDS AND SOLDER-JOINTS IN QFNs

摘要

QFN packages have found extensive applications in automotive and defense electronics. Electronic components comprise many material-interfaces between EMC (Epoxy mold compound), wire bonds, aluminum pads, silver die, die attachment adhesive and lead frame. Making traditional CAD model, mesh and FE models for electronic packages is time-consuming. In addition, nominal modeled geometry may not include manufacturing variabilities from molding and bonding processes. In this paper, a new method to create finite-element models based on x-ray micro-computed tomography data of the actual part assembly has been presented. The method has been applied to assembled QFN parts for assessment of stresses at various interfaces and solder joints during thermal cycling. Effect of EMC properties on the stresses at the various interfaces, Cu-Al wirebond interconnects, and solder joints in the presence of voiding has been studied. Life prediction has been pursued using the inelastic strain energy density based damage relationship. The model has been validated with experimental data.