Development of 3D Wafer Level Package for SAW Filters Using Thin Film Lamination

As the accelerating development of mobile communication, 3D wafer level packaging (3D-WLP) has attracted much attention since it can provide smaller form factors, lower cost and better electrical and thermal performance.In this paper, the design and process development for an ultra-small 3D-WLP with the size of 1070 μm×920 μm ×355 μm for a SAW filter was comprehensively studied. In the present package, thin dry films were used to generate a gas-filled cavity structure, which provided a stable and safe environment for the interdigital transducers (IDT) structure from the contaminants or corrosions to ensure reliability. Through film via interconnects were formed to contact the chip's pads and the solder balls formed with the Ni/Au under bump metallization (UBM). Finally, the wafer was diced into individual packages.Finite element modeling (FEM) was used to simulate the mechanical stress during the actual packaging process. The effects of cavity structure and geometric parameters on the peeling stress values were studied using FEM, and some recommendations were given for package structure optimization. Based on the above studies, the optimized SAW packages successfully passed the reliability test of pre-con level 3.