Abstract
Reliability requirements for harsh environment electronic packages are increasing with the use of electronics in automotive underhood. The underhood includes various safety and critical functions such as automated locking systems, electronic fuel injection systems, engine control units, and anti-lock braking systems. Pad cratering manifests with initiation and propagation of micro-cracks beneath the BGA packages in the organic printed circuit boards. Major factors of these cracks formed with the combination of thermal cycling, shocks, vibrations, incorrect design or material selection, and manufacturing defects. In this investigation, the problem of pad cratering has been systematically approached by analyzing the bulk behavior of the resins using a tensile dogbone specimen and then moving forward with a bent specimen for the glass-resin interfaces. The first bulk study consists of 12 different resin formulations in which material property changes were studied under two and six reflow cycles. In the second part, a four-point bend interface specimen was used. The effect of reflow cycles was investigated by reporting perc-change in the Mode-I stress intensity factor and using this metric to rank the interfaces. In the end, an effort was made to create a predictive regression model with predictors being material properties of the samples such as elastic modulus, toughness, UTS, elongation of the resins, glass transition temperatures, and environmental conditions such as reflow cycles.
