First MCM-D modules for the b-physics layer of the ATLAS pixel detector

The innermost layer (b-physics layer) of the ATLAS pixel detector will consist of modules based on MCM-D technology. Such a module consists of a sensor tile with an active area of 16.4 mm/spl times/60.4 mm, 16 read out ICs, each serving 24/spl times/150 pixel unit cells, a module controller chip (MCC), an optical transceiver and local signal interconnection and power distribution busses. We show a prototype of such a module with additional test pads on both sides, The outer dimensions of the final module will be 21.4 mm/spl times/67.8 mm. The extremely high wiring density which is necessary to interconnect the read-out chips was achieved using a thin film copper/photo-BCB process on the pixel array. The bumping of the readout chips was done using electroplating PbSn. All dies are then attached by flip-chip assembly to the sensor diodes and the local busses. This thin film technology has been described previously and is under further development at Fraunhofer-IZM in Berlin. The focus of this paper is the description of the first results of such MCM-D-type modules.