Effect of Viscosity and Fillet Size of Board-Level Underfills on Reliability of BGA Assemblies
Authors: Saeed Akbari, Amir Nourani, Jan K. Spelt Company: Department of Mechanical and Industrial Engineering, University of Toronto Date Published: 5/19/2015
ICSR (Soldering and Reliability)
Abstract: BGA/PCB assemblies underfilled with silica-filled and unfilled epoxy adhesives were tested in a double cantilever beam (DCB) configuration to investigate the effect of fillet on the fracture load and the failure pattern. Two different failure modes were observed. For relatively small fillets, the crack initiated and propagated along the solder mask / PCB interface. For larger fillets, the crack propagated within the PCB at the interface between the epoxy and glass fiber of the prepreg layer at a higher load. The results show the importance of the underfill viscosity and the corresponding fillet size on the reliability of the underfilled BGAs.