The detector/readout-electronics assembly of the eXTP Wide Field Monitor

One of the four instruments on the Chinese-European enhanced X-ray Timing Polarimetry (eXTP) mission is the Wide Field Monitor (WFM), consisting of 6 coded aperture cameras. The detector plane of each camera is comprised of four 7x7 cm(2) silicon drift detectors assembled with similarly sized hybrid circuit board that contain the front-end electronics (FEE) to read out the detectors. The whole assembly needs to be positioned and kept stable within similar to 50 micron to guarantee the scientific performance of the WFM. The FEE will have analogue ASICs to perform the read-out process. These bare dies are connected to the detector anode output pads. The detector cathodes need to be provided with voltages down to -1300V. Electrical connections between detector, ASICs and FEE are made by bond wires. The hybrid circuit board is a thick film circuit based on 96% Al2O3 which has a coefficient of thermal expansion that is sufficiently close to that of the silicon detector to avoid misalignment due to the large variations in temperature (-50/+60 degrees C) during assembly and flight. All materials, components and manufacturing processes will have to be without technology originating from the USA. For eXTP's phase B, we are developing a Demonstration Model. For this, an early generation ASIC ('IDeF-X HDBD') is employed as well as some components that are US-made but for which there is path to European alternatives. The FEE manufacture and the assembly is already completely non-US. We outline the detector/electronics assembly and discuss the main challenges involved.