Flexible front-end hybrids for the CMS outer tracker upgrade

The upgrade of the CMS tracker for the HL-LHC is based on a binary readout scheme using the CMS Binary Chip (CBC2). The connectivity requirements of this flip-chip ASIC requires the use of high density interconnecting hybrids. Module integration studies indicated that a foldable flexible hybrid circuit results in an optimal module arrangement. A full module size HDI flexible hybrid was designed, integrating eight CBC2 ASICs. The hybrid is fitted with carbon fiber stiffeners and a sharp folding allows connecting the two strip sensor wirebond arrays. The front end circuit development was focused on the 2 Strip (2S) module electronics. This paper will present the implementation of the 2S front end electronics on a flexible substrate covering the mechanical and electrical properties of the assembly.