Evaluation of Die Strength by Using Finite Element Method With Experiment Validation

Abstract

3-D chip stacking packaging is becoming increasingly popular in the electronics packaging industry because the demand of current market has focused on cheaper products with higher performance characteristics and smaller form factors. Silicon wafers must be ground using wafer-thinning processes to achieve smaller packaging sizes. However, cracks may form in the silicon chips during stacking or while the device is in use. In this paper, the ball-breaker test is used to determine the maximum allowable force on a (1 0 0) silicon die. Finite element (FE) analysis using the commercial software ANSYS/LS-DYNA3-D is introduced to calculate the strength of the silicon die and compared with the experimental findings shows that the results are consistent with Hertzian contact theory. The effects of silicon die thickness and foundation material on the silicon die strength are also discussed in this paper. As the applied force increases, a crack appears on the edge of the contact area and propagates within the die. A decrease in die thickness results in the formation of radial cracks on the bottom surface as well as significant bending effects on the test die. The initial failure may originate from the radial crack and propagate toward the top surface of the die leading to die breakage. The strengths determined in this experiment decrease as the test die becomes thinner. Furthermore, if the insignificant bending behavior is observed, simulation results show that the maximum allowable force on a silicon die increases when a softer foundation material is used. However, a thin test die placed on a soft material is considerably easy to break because the tensile stress on the bottom surface of the die caused by the rapid increase in bending behavior significantly affects die breakage.