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In this paper, the reliability of a pyramidal-shape three-die-stacked package with through-silicon via (TSV) is studied experimentally and numerically. The initially designed microbumps are located peripherally along the edge of the TSV die, which induces a concentrated bending force on the lower die when the upper die is stacked. Finite-element (FE) simulation results show that such bump layout induces large stress and deflection in the lower die under the die-stacking process. Three-point bend tests were conducted to determine the die strength. Die-stacking experiments were also carried out. The experimental results show that the bottom die cracks when the middle die is stacked and the middle die cracks when the top die is stacked even with a small stacking force. Consistent results have been obtained among FE simulation, die strength bend test, and die-stacking experiments. An optimal bump layout design is proposed, which adds some dummy bumps on the central area of the die to support the bending force induced by the die-stacking process. The optimal design significantly reduces the die stress level and deflection. Finally, a successful die-stacking process is achieved even using a larger stacking force.