  The Simons Observatory (SO) is a suite of instruments sensitive to
temperature and polarization of the cosmic microwave background (CMB) to be
located at Cerro Toco in the Atacama Desert in Chile. Five telescopes, one
large aperture telescope and four small aperture telescopes, will host roughly
70,000 highly multiplexed transition edge sensor (TES) detectors operated at
100 mK. Each SO focal plane module (UFM) couples 1,764 TESes to microwave
resonators in a microwave multiplexing (uMux) readout circuit. Before detector
integration, the 100 mK uMux components are packaged into multiplexing modules
(UMMs), which are independently validated to ensure they meet SO performance
specifications. Here we present the assembly developments of these UMM readout
packages for mid frequency (90/150 GHz) and ultra high frequency (220/280 GHz)
UFMs.
