Evaluation of contact resistance of silver-loaded epoxy with aluminized backplane of silicon microstrip sensors

Some modules of the ATLAS silicon strip detector (SCT) exhibited a significantly higher effective bias resistance than we had expected. About 20 % of the barrel modules, for instance, showed such a resistance of 40 Omegak or higher. We have tried to identify causes of this high resistance as well as to find a remedy if necessary. As for the SCT modules, the bias connection is made with silver-loaded epoxy to the aluminized backplane of the silicon sensors. It was identified that the contact of the silver-loaded epoxy to the surface of the aluminized backplane sometimes provoked the high resistance. Fortunately, however, it automatically cures in practice by applying a usual bias voltage, to become harmlessly small of a few ten ohms.