Optimizing Die Corner and Optical Groove Corner Crackstop Support Structures for Mitigating Dicing and CPI Risks

An experimental correlation showing flipchip packaged larger dies more susceptible to corner delamination is, first, established in this work. Chamfer structures have been inserted into the architecture of traditional orthogonal crackstop designs with the aim to alleviate the accumulation of strains present in the corners of larger dies. Finite element modeling (FEM) was employed to uncover the optimum chamfer structure size that minimizes both the chamfer space usage as well as chip package interaction (CPI) related risks. Die size was shown to have quantifiable impact on the corner strain. The effect of die size was shown to be enhanced with lower underfill modulus. The effect of changing the crackstop corner chamfer structure size on both corner strain and strain energy release rate was studied. While varying the crackstop corner chamfer structure size had minimal effect on strain, it did have a significant effect on the strain energy release rate. It was observed that chamfer structure significantly reduces the strain energy release rate at the edge of the die near the corner. It has been determined that the optimum location for the support structure triangle vertex is to be situated at the point where the peeling strain switches from compressive to tensile at the corner square. The effectiveness of corner chamfer support structures in reducing CPI risk at the optical attach cavity used for lateral optical fiber attach was evaluated. The simulations have determined that inclusion of crackstop corner support structures at the newly created internal cavity corners of the die result in a reduction of the average corner strain by 33% at the external corner and 21% at the internal corner of the optical cavity.