| Summary: | 碩士 === 中原大學 === 機械工程研究所 === 96 === This investigation describes about the effect of different shape solder ball on stress in flip chip packaging. The stress developed in then used to evaluate the fatigue life.
ANSYS has been implemented to study the von Mises stress an Shear strain behavior and fatigue life of pin shaped solder ball in flip chip package under mechanical and thermal stress. Twenty-seven different parameters such as solder ball shape, size etc. has been considered for simulation. The stress/strain behavior is initially studied at thermal load 25C to 125C. The thermal distribution obtained from the thermal analysis is used to simulate the structural analysis to acquire mechanical stress/strain behavior. Coffin-Manson fatigue formula is used to optimize the life of solder balls in flip chip package.
The stress/strain behavior of twenty-seven pin shaped solder balls having same diameter but different heights, different solder ball separations and different distances of solder balls to the edge of a chip is studied. The optimized result is obtained with the solder ball having diameter = 0.075mm; height= 0.121mm and the ball pitch 1.135mm and the distance of solder balls to the edge of a chip 0. 5mm. The maximum values of von Mises stress and shear stress are calculated to be 54.594 MPa and 6.016 MPa respectively. The fatigue life is determined to be 253706 cycles in the optimized structure. The analysis process points out that the height of solder ball, intervals between solder ball, and distance of solder ball to the chip edge influence the fatigue life. This suggests that special attention has to be given on these parameters during the design of the structure in Flip Chip.
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