LHCb VErtex LOcator module characterisation and long term quality assurance tests

LHCb is the dedicated b-physics experiment of the LHC. Its vertex detector, the VErtex LOcator (VELO), will operate in a harsh radiation environment with limited access due to its proximity to the LHC beam. To ensure the long term operation and performance, every module was required to pass a set of quality assurance tests. These were specifically developed for the VELO modules to take into account their operational environment and assembly steps. Each VELO module was rigorously inspected, tested and thermally cycled in the Glasgow module burn-in procedures. This paper provides details of the burn-in procedures and summarises the main results that were found. Some of the major results presented in this paper are: the full characterisation of the leakage currents; identification of bad channels; and signal to noise measurements. A few minor problems were identified through visual inspections of the modules and the feedback into the production process proved critical. As a result of the electrical and thermal tests, one module out of the 45 that were tested was rejected due to its thermal performance. Studies are also reported, based on individual modules, characterising the front end read out chip pulse shape.