Abstract
3D or stacked-die packages are becoming increasingly popular in the electronic packaging industry because of the current market demand for cheaper and smaller products with high performance characteristics. As the result, the IC silicon wafers should be thinned through wafer-thinning processes to achieve greater packaging density, such as etching, grinding and polishing. However, it is possible to induce crack of the chips during manufacturing process. Therefore, this study aims to determine the strength of silicon die which can provide a design guideline to prevent the silicon die failure problem. Several methods have already been adopted to determine the strength of silicon die. These methods include three-point bending test (3PB), four-point bending test (4PB) and ball-breaker test. However, 3PB and 4PB have difficulty for application not only in experiment set ups and silicon dies preparation but also in actual use because both edge and surface defects will influence the stability of strength evaluation. Therefore, the ball-breaker test is then proposed with the acoustic emission system (AE system) in this study to measure the allowable force of silicon die as the initial crack occurs. Besides, the failure modes of silicon die under different contact forces are also discussed in the study. Meanwhile, comparing with experiment data, the finite element method (FEM) analysis using commercial software ANSYS/LS-DYNA3DR are introduced to determine the silicon die strength. Moreover, the 3D model of the ball-breaker test is verified through the Hertzian contact theory. The strength of silicon die with different thickness and crystal orientation are determined through the methodology of this study. Moreover, the factors that influence the experiment results through ball-breaker test are also investigated. The results show that the area and the edge defect of silicon die have no effect on the strength determination. However, the roughness of silicon die influences the results. As the roughness increases, the die strength decreases because stress concentration at the rough part on the surface will cause the die failure. Furthermore, based on the strength of silicon die with different thickness in this research, the simulation results show that the allowable force of silicon dies increases as the softer foundation material is applied due to the softer foundation has better capacity for absorbing the contact force. However, the failure of the thinner test die placed on the softer foundation is much easier to happen. This is because the tensile stress on the bottom surface of thinner die resulting from the bending behavior increases rapidly and significantly influences the die breakage. Overall, the influence of the foundation material decreases as the silicon die thickness increases.