Development and Reliability of Wafer-Level SAW Filter Packaging Using Photosensitive Films

The development of 5G era has set higher standards for existing radio frequency (RF) packaging technologies, driving wafer-level packaging (WLP) toward small size, enhanced performance, and lower cost. In this work, a new 3-D WLP solution based on photosensitive films was presented to resolve reliability issues for surface acoustic wave (SAW) filters. A high-strength photosensitive dry film (Roof A), characterized by its high modules of elasticity and excellent pressure resistance, was selected as the roof layer. Meanwhile, a complementary photosensitive film (Wall D), optimized for compatibility with Roof A, was used as the wall layer. Finite element method (FEM) simulations were conducted to evaluate roof layer deformation under various conditions, including different roof and wall layer materials, wall layer thicknesses, and aperture ratios during the reflow process and molding experiment. The results confirmed the superior properties of Roof A and Wall D, which were successfully implemented in the packaging structure. Moreover, the packaged chip passed rigorous reliability tests, paving the way for the mass production of this innovative packaging solution.