Construction of the ATLAS SCT Endcap modules

The ATLAS Semi-Conductor Tracker (SCT) uses silicon strip detectors to measure trajectories of charged particles coming from 14 TeV proton–proton collisions at the Large Hadron Collider at CERN. The SCT provides at least four space points, in the radial range of 27–50 cm from the beam, for tracks within the angular acceptance |η|<2.5. The SCT is built up of 4088 modules, each consisting of two or four silicon detectors, a hybrid carrying several readout ASICS, and other components to support, cool and align the detectors. We report on construction of over 2000 end-cap modules of the SCT by a group of 14 institutes from seven countries. A key aspect of the project was to fully standardise the final module tests and to insist that test data from all institutes was stored in a single central database, while leaving institutes flexibility to vary their module assembly methods to suit local circumstances. First the module specifications and tests used for quality control are summarised, then we describe the main test results. Finally, we report our experience in terms of component quality, assembly and testing rates, yield of good modules and causes of lost modules. At the outset we assumed losses during assembly of 15% and procured components accordingly; in fact, losses were around 7%.