A Novel Zero-Level Packaging using BCB Adhesive Bonding and Glass Wet-Etching for Millimeter-Wave Applications

This paper presents zero-level packaging by using wafer-level BCB adhesive bonding and a pyrex glass wet-etching technique. A novel MEMS packaging process was developed to fabricate housing cavities in a pyrex glass wafer and use BCB sealing rings on the pyrex to bond on the MEMS wafer. The BCB sealing ring is processed before the cavity formation. During a wet-etching of glass for cavity and pads feedthroughs formation, BCB was protected by 1.2 mum - thick AZ 1512 photoresist. The wafer level bonding and dicing encapsulation glass cap have completed the packaging. The bonding strength has been estimated to about 4 MPa for an implemented package dimension. To characterize a pyrex # 7740 packaging material in W-band, a 50 Omega coplanar waveguide (CPW) was designed and fabricated. The measured insertion loss (SI2) was - 0.3 dB / mm at 60 GHz. The RF characteristics of the glass packaged CPW line have been also measured to investigate the effect of the package at high frequencies. It shows that the insertion loss change of CPW lines by the package is below 0.1 dB from DC to 110 GHz.