Approaches to wafer level packaging for SAW components

Truly die-size wafer level packages for surface acoustic wave (SAW) devices are necessary due to stringent size, weight, and price requirements. Recent approaches are presented that feature a bottom and cap wafer both made of the same piezoelectric material. The wafers are adhesively or eutectically bonded with, respectively, polymer or copper frames acting as spacers that ensure the obligatory cavities above the acoustic structures. Variants of these basic structures allow for the integration of coils within the packages. Due to its extremely compact realization a component - consisting of a first die with the acoustic structures and a second die forming the cap that optionally includes integrated coils - demands for extensive model building and sophisticated simulation tools in order to capture its electromagnetic couplings. The complex models comprise the 3D line crossings on the die as well as the 3D interconnects between the dies. Such complex simulations have been the base for both successfully developing the packaging technologies and optimizing the performance of the concrete components. Examples of application to duplexers will be shown.