Surface micromachined membranes for wafer level packaging

Novel surface micromachined membranes have been developed for wafer level packaging and polymer encapsulation. Laterally unconstrained electroforming allows small etch holes to be included in thick membranes whilst only requiring a thin, low stress, mould. These holes have been shown to have a sufficiently small aperture (<10 µm) and depth (17 µm) to block a high viscosity encapsulant (AZ4562 photoresist). However, they enable the low viscosity sacrificial release etchant (acetone) to pass through. Etch hole inclusion provides a rapid and clean release. In order to route interconnect to the membranes, side port flow channels have been developed which effectively block spin-on encapsulants from entering the protected cavity. The influence of the membranes on the RF performance of micromachined meander inductors is reported.