Predicting reliability behavior in HBM packages through numerical simulation

A typical HBM (High Bandwidth Memory) package consists of multiple memory dies in a stack formation. A passivation material may be inserted between the dies by laminating each with a NCF (Non Conductive Film) prior to stacking. This enables a thin joint gap, and therefore a higher number of stacked dies in keeping with increasing density demands. Of particular interest in the present study is the interface between an Si die and adjacent NCF in a 2.5D SiP arrangement. These interfaces may carry the risk of acting as sites where cracks could form if exposed to a severe load or high stress. It is necessary to quantify their robustness and ensure their reliability during processing and end-user applications. We employ FEM(Finite Element Method) simulation to investigate the degree of stress created by a thermal load in HBM packages. Simulation is also employed to model the path by which moisture is absorbed into the NCF -Si interface. We then combine these considerations into an Interface Reliability Index which quantifies and predicts the reliability at any given site along the NCF -Si interface. The same parameters are also incorporated into a TC (Thermal Cycle) Index, which predicts the fail cycle under TC load at the same interface. Both Indices demonstrate a high degree of correlation with experimental results. This makes them a highly useful tool to quantify and predict the reliability behavior of HBMs in various arrangements and conditions. As such, it becomes possible to optimize the geometry and materials of each component for maximum resilience, and to ensure that even the most severe reliability demands and requirements are met or exceeded.