Predicting delamination in multilayer composite circuit boards with bonded microelectronic components

The present work developed a mixed-mode cohesive zone model (CZM) with a mode I failure criterion to predict the delamination bending loads of multilayer, composite printed circuit boards (PCBs) assembled with soldered ball grid array (BGA) components that were reinforced with an underfill epoxy adhesive. Two different delamination modes were observed in these microelectronic assemblies: delamination at the interface between the solder mask and the first conducting layer of the PCB, and PCB subsurface delamination at the interface between the epoxy and glass fibers of one of the prepreg layers. The cohesive parameters for each of the two crack paths were obtained from fracture tests of bending test specimens consisting of PCB substrates bonded with the underfill adhesive. The model provided relatively accurate predictions of the crack paths and the bending strength of the actual underfilled BGA-PCB assemblies for a range of adhesive fillet sizes, PCB stiffnesses, and strain rates.