Wirebondability enhancement for very small die in power packages with dynamic simulation

摘要

As microelectronics is moving towards miniaturization, function integration and cost reduction, the device itself is becoming smaller while keeping same or even more functions. Silicon die with area less than 2×2 mm is common. This poses challenges for very small die handling and assembly. In another respect, high reliability is required for power packages especially for automotive application. During the development of a new power package module (with 2 devices), wire bondability issue is encountered for the smaller device (1.8×1.9 mm), while the bigger die is not affected. After continuous effort, root cause analysis is focused on the softening of die attach glue material during high temperature wire bonding process. Finite element modeling is used to understand the dynamic behavior of the module during wirebonding. Both modal analysis and harmonic analysis have been performed. Modeling results confirmed the dynamic effect of glue softening. Results show dynamic response along Y-axis is much higher than that along X-axis, which correlated well with experimental observation. Further optimization has been carried out on package geometry and glue material properties, which leads to assembly guidelines on material selection and process control. Successful product qualification well demonstrated the benefit of numeral simulation for advanced package development.