Mechanism of wire bond shear testing

摘要

Shear testing of wire bonds in microelectronics devices is important in bonding process qualification, but the actual mechanism of shearing Cu bonds from Al pads is not thoroughly understood. In this study, experiments and finite element analysis (FEA) are employed to develop a deeper understanding of shear testing and its change with bond degradation. Thermosonic ball bonding on Al pads causes Al deformation, including thinning beneath the bond and Al “splash” to the sides, while forming the weld through intermetallic compound (IMC) formation. Pad Al thickness and IMC area are both important factors for shear force of as-bonded circuits, explained by simulations calibrated to experimental data of destructive shear testing. Shear test results after reliability stress testing, are compared with shear force of un-aged bonds, along with post shear images. Result shows an initial increase in bond shear force up to 168 h in most bond recipes, after which it drops. Explanation of the observed trend is provided along with recommendation of effectiveness of bond shear test method.