A novel packaging method using wafer-level BCB polymer bonding and glass wet-etching for RF applications

This paper presents a zero-level packaging method using Pyrex glass wet-etched with pre-defined benzocyclobutene (BCB) sealing rings in the wafer level to obtain a denser packaging cap. Contrary to the conventional process, a polymer-sealing ring was patterned before a housing cavity formation on a glass wafer. As the number of housing cavities on the packaging cap increases, it is difficult to make a fine sealing ring on a cavity-formed wafer due to a topographical problem. The pre-defined BCB sealing ring was protected by a 1.2-μm thick AZ1512 photoresist while the glass-packaging cap was wet-etching for the housing cavity. The average thickness of the BCB bonding layer after removing the AZ1512 resist was measured at 5.14 μm. Packaging was accomplished by bonding at 250 °C for 1 h before a glass cap was half-diced for pad access. ANSYS simulation has shown a bonding strength of approximately 4 MPa for the implemented package dimension. To characterize the Pyrex #7740 packaging material in the W-band, a 50-Ω coplanar waveguide (CPW) was designed and fabricated. The measured insertion loss (S12) was −0.3 dB/mm at 60 GHz. The RF characteristics of the proposed glass-packaged CPW line have also been measured to investigate the effect of the package at high frequencies. It shows that the insertion loss change of CPW lines with the packaging is below 0.1 dB from DC to 110 GHz.