Prediction of pad cratering fracture at the copper pad - Printed circuit board interface

Pad-crater fracture was characterized in terms of the critical strain energy release rate, J _ci, measured at various mode ratios, ψ. Specimens were prepared from lead-free chip scale package-PCB assemblies and fractured at low and high loading rates in various bending configurations to generate a range of mode ratios. The specimens tested at low loading rates all failed by pad cratering, while the ones tested at higher loading rates fractured in the brittle intermetallic layer of the solder. The J _ci of pad cratering increased with the phase angle, ψ, but was independent of surface finish (OSP and ENIG) and reflow profile (time above liquidius 60 s and 120 s). The generality of the J = J _ci(ψ) failure criterion to predict pad-cratering fracture was then demonstrated by predicting the fracture loads of single lap-shear specimens made from the same lead-free assemblies.