Sensitive and robust heterodyne mixers are needed for future atmospheric remote sensing missions. This data from satellites such as NASA's Earth Observing System (EOS) lends great insight into molecular interactions in our environment. The Microwave Limb Sounder (MLS) on EOS will detect radiation emitted from 03, ClO, and OH molecules which are critical to our understanding of ozone depletion and greenhouse warming. The heterodyne mixers on MLS must exhibit sufficient spectral sensitivity, wide bandwidth, low noise, and minimal LO power requirements. Planar GaAs Schottky diodes currently are the most promising technology for space-borne radiometers where cryogenic cooling is not desirable. In this work we present progress on a novel wafer bonding technology, MASTER, used to integrate submillimeter wavelength planar GaAs Schottky mixer diodes with quartz microstrip circuitry. Problems associated with wafer expansion after bonding, open- circuited devices, and Ti/Pt/Au metallization removal have been solved and device yield is significantly improved. FTIR measurements of the bonding adhesive's properties at submillimeter wavelengths are discussed. We have fabricated 640 GHz subharmonic mixers for EOS-MLS which nearly match state-of-the-art performance at this frequency with DSB Tmix equals 2396 K and Lmix equals 10.98 dB using 4.67 mW of LO power. RF testing of a new higher yield batch of MASTER mixers is in progress.