Wafer Level Package with Polymer Sealed Air Cavity

A wafer level package (WLP) with polymer sealed air cavity was demonstrated with high modulus photo-dielectric film. Different polymer sealed air cavity sizes with and without support features were fabricated and Cu redistribution layer was processed over the cavity structures to form the WLP with fan-in RDL and solder bumps interconnects. The fabricated test packages were subjected to surface profile measurement to measure deflection of the polymer sealed air cavity under reflow condition. The cavity structures with wall support features shows lowest deflection at reflow temperature when compared to pillar and no support. In all cases, the cavity surface profiles restore to its original states when cooled down reflow temperature. Test packages were subjected to reliability tests; moisture stress test level 3 and liquid to liquid thermal shock of 100 cycles. C-SAM imaging shows no ruptures of the polymer sealed cavity structure after the reliability test. These results indicated that the high modulus film is able to endure RDL processing, solder reflow temperature and reliability test conditions.