Wafer-level-package for Bulk Acoustic Wave (BAW) filters

Silicon based Bulk-Acoustic-Wave (BAW) filters utilize mainstream wafer processing and can create significant customer benefit in terms of cost, performance and size. Similar to conventional SAW filters the package is a dominant cost contributor as long as ceramic cavity packages are used. For both SAW and BAW the active area may not be coated with any package material. We report on an innovative process which enables to manufacture BAW filters in cheap plastic SMD packages similar to packages in use for diodes and transistors. Our process is based photo-epoxy SU-8 which allows to build air-cavities above the active areas of a filter. The process is cheap as it is done on wafer level and fits well into a CMOS manufacturing environment.