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This paper presents a wafer scale low-loss and broad-band RF MEMS packaging technology developed at MIT Lincoln Laboratory. The fabrication includes CMOS compatible front-end processing and thick Au backend processing. Au thermo-compression bonding is used to mate a metal coated capping wafer to a device wafer, offering high-isolation and low-loss transmission lines within the cavity. Hermetic thru-wafer vias carry the RF signal in and out of the package through the 25 μm-thick device wafer. We demonstrate a packaged 100 μm-long transmission line with 0.06 dB and 0.1 dB total insertion loss at 20 GHz and 50 GHz, respectively. The packaged transmission line has 0.96 dB/cm attenuation at 40 GHz and less than ± 1 degree phase error from DC to 50 GHz for a 10.8 mm-long line. The isolation of closely spaced lines is also presented. Hermeticity is evaluated with in-situ moisture sensors after exposure to an autoclave environment for 4 hours.