BGA SOLDER JOINT FRACTURE AS A FUNCTION OF STRAIN RATE AND PCB RIGIDITY

摘要

Package-on-board systems utilize printed circuit boards (PCBs) with different rigidities depending on the application of the product. This study investigated the effect of PCB stiffness on the fracture loads of ball grid array (BGA) solder joints over a range of strain rates. Fracture experiments under bending loads were performed using specimens with 1, 2 or 3 laminated PCBs, each 1 mm thick. Intermediate strain rates (0.2-0.6 s~(-1)) were achieved using a servo-electric machine, while a drop tester was used for high strain rate (30-50 s~(-1)) experiments. A strain-rate dependent cohesive zone model was calibrated using the measured fracture load of one specimen with 1 or 2 laminated PCB(s) in each of these strain rate regimes. This model was then used to predict the fracture loads of the specimens with 2 or 3 laminated PCBs. The predicted fracture loads agreed reasonably well with the measured values, being within 12% and 15% of the measured forces for intermediate and high strain rates, respectively. The cause of the residual error was believed to be the inability of the model to account for changes in adherend rigidity which would affect the solder joint constraint and hence the extent of its plastic deformation.