Optimization of through-silicon via structures in a fingerprint sensor package

Abstract: The through-silicon via (TSV) is a type of vertical electrical connection that can pass through a silicon wafer or die. By using TSVs, compared to using wire bonding as interconnections in a capacitive fingerprint sensor, the capacitive strength between the sensor die and the finger can be increased. However, since TSV structures are both more complex as structures and have a more complex manufacturing process compared to wire bonding, reliability can be an issue. This thesis studies a TSV structure that failed qualification in where the aim was to find the root cause of the failure and to find how the material parameters affect the reliability of the TSV. A set of changes in process steps and materials used have been evaluated both by cross-section analysis and thermomechanical finite element analysis (FEA) simulations. The root cause of the failure could not fully be determined, but the cross-section analysis and FEA simulations showed that the usage of low coefficient of thermal expansion (CTE) polymers and high modulus trench fill could reduce the delamination ratio in the TSV.