Abstract
Pad cratering is one of the major failure modes encountered during PCB assembly and operation. Fracture is generally mechanically induced between the outermost layer of board resin and copper foil, between the resin and the glass fibers, or in the bulk resin of the printed circuit board. Prior work on the reliability of printed circuit board assemblies focuses on solder joint fatigue. However, data on the reliability of pad cratering and predictive models on expected pad-crater propensity are scarce. Mechanical characteristics of the copper/resin interfaces and bulk resin material evolve with reflows. Pad cratering at copper-to-resin interfaces with respect to reflows has not been studied widely yet. Ten distinct bulk resin materials have been investigated to compute the evolution of bulk resin properties. Copper-to-resin interfacial samples have been tested under four-point bend loading with respect to reflow conditions. The evolution of bulk resin properties has been considered for computing the evolution of copper/resin interfacial properties. The steady-state energy release rate and Interfacial Fracture Toughness are determined for each testing condition. This research would be useful in proposing a copper/resin interface combination that is more reliable against pad cratering. Based on the data captured, a predictive regression model has been developed to predict the material combinations providing the best reliability against pad cratering.
