Fracture load prediction of BGA solder joints: Cohesive zone modeling and experimental verification

Abstract

• BGA test vehicles were prepared in a standard surface mount technology line. • Specimens with different geometries tested under various test configurations. • A strain-rate dependent cohesive zone model was developed. • The model was calibrated using one experimental data point. • The model was validated at arbitrary geometries and loading conditions. Ball grid array (BGA) test vehicles, assembled in a standard surface mount technology (SMT) line, were used to prepare fracture specimens in seven configurations in order to measure solder ball fracture loads at two different strain rate regimes for a range of loading mode ratios. The measured strengths of the specimens were compared with the predictions of a cohesive zone model (CZM). The phase angle of the specimens under bending was found to be close to mode I and hence the fracture criterion was governed predominantly by mode I parameters. The mode I peak stress and fracture energy of the CZM were obtained in two separate ways: (i) The fracture energy was obtained from separate copper-solder-copper double cantilever beam (DCB) tests, while the peak stress was obtained from one of the BGA specimen configurations. (ii) One BGA specimen configuration was used to obtain the mode I fracture energy, and the peak stress was assumed to be given by the yield stress. In both cases (i) and (ii), the rising slopes of the modes I and II traction-separation laws corresponded to the compliance of the system. The accuracy and generality of these CZ models was then assessed by using them to predict the fracture loads of the remaining BGA specimens that had different geometries and hence fracture strengths. The fracture loads predicted using either model were in reasonable agreement with the measured forces at a given strain rate. Therefore, once the CZM parameters have been defined for a given solder system using one BGA specimen, the CZM could predict the fracture of BGA solder joints with different geometries and strengths.