Design Optimization of a Wafer Level Package for Surface Acoustic Wave Filters

In this paper, wafer level packaging of a surface acoustic wave (SAW) filter is considered. Numerical studies based on a three-dimensional finite element method (FEM) have been conducted in order to evaluate the reliability of a wafer level SAW package. The effects of package geometric parameters, such as the diameter of via hole and wafer thickness, on the reliability of the wafer level SAW package have been studied. The results show that the diameter of via hole for interconnection plays a key role in the reliability of the SAW package because the CTE mismatch between the filling materials of via holes (copper) and surrounding cap wafer martial (LiTiO3) is the highest among the material pairs in the package. Such CTE mismatch leads to the maximum stresses and warpages. The optimal thermo-mechanical properties of packaging materials have been proposed to achieve the minimum thermal stress during reflow process. Moreover, numerical results have also been compared with the experimental ones to validate the FEM model.