Effects of resin thickness on the stress intensity factors of edge-cracked adhesive joints

The effects the thickness of epoxy resin on the stress intensity factors (SIFs) of the edge-cracked adhesive joints subjected to external loads are investigated in the current paper. The three-layered joints composed of Silicon, epoxy resin and FR-4.5 are widely seen in the package solutions of CSP/FBGA for electronic devices. Cracks or delaminations from resin-substrate interface or resin-silicon interface are the common failure modes in plastic IC packages. However, it is difficult to determine the exact stress state of a bi-material interface due to the oscillatory singularity. In this paper, the SIFs of the single edge-cracked joints are determined accurately by using the Crack Tip Stress Method. Then, the effects of resin thickness on the SIFs of various edge interface cracks under uniform tension are investigated by varying the resin thickness and crack length. It was found that the SIFs grow with the increment of resin thickness and reach constants when the resin thickness is larger than the width of the joint.