Overview of the HL-LHC CMS outer tracker upgrade and lessons learned from 2S module production

For operation at the High-Luminosity LHC, the CMS collaboration is developing a significantly enhanced silicon detector system with improved radiation hardness, higher granularity, and extended coverage up to a pseudorapidity of |eta| < 4. The Outer Tracker will be equipped with two types of modules (2S and PS) that will provide tracking information to the L1 trigger of the HL-LHC CMS detector, by rejecting signals from particles below a certain transverse momentum threshold. Hence, these modules must be assembled with high precision and have to pass strict requirements. In this note, an overview of 2S module production is presented, as well as representative examples of problems and experience acquired during module assembly and performance tests.