JINST JINST Hybrid circuits for the CMS tracker upgrade frontend electronics Blanchot G CERN 2013 8 The upgrade of the CMS tracker at the HL-LHC requires the design of new front-end modules to cope with the increased luminosity and to implement L1 trigger functionality. The new modules under development are based on high density hybrid circuits with new flip-chip front-end ASIC, and are wire bonded to strip sensors and connected to a service board for the data transmission. The suitability of different substrate technologies considered for the design of the hybrids is discussed, aiming for a cost effective and reliable manufacturability of the CMS tracker modules. research-article