Development and Reliability Study of 3-D Wafer Level Packaging for SAW Filter Using Thin Film Capping

The rapid growth of the advanced consumer 5G wireless mobile phones has propelled the demands of fabricating surface acoustic wave (SAW) filters with smaller size and high performance. Three-dimension wafer-level package (3-D WLP) for SAW filter is a promising solution to replace conventional surface mounted technology and chip-scale packaging. In this article, a new WLP for SAW filter with a size of 1.3 mm $\times1.1$ mm $\times0.35$ mm is developed using thin dry film capping. The new 3-D WLP significantly reduces the overall thickness which is particularly meaningful for low-profile smartphones and tablets. A number of key processes were developed. To improve the quality, finite element modeling (FEM) is used to simulate the mechanical stress to optimize cavity structure. Reliability tests were performed and the results indicated that there were no significant frequency response changes occurred and low insertion loss (IL) in pass band was less than 0.2 dB after pro-conditional level 3 test, unbiased highly accelerated stress (uHAST) test, and temperature cycling (TC) test on SAW filter packages. It can be concluded that 3-D WLP for SAW filter achieves miniaturization, good electrical performance, and reliability.