Speaker
Description
The Wide-Field-Imager (WFI) instrument is one of two instruments planned to fly on the ATHENA observatory. At its current capabilities, WFI can image incoming X-ray photons in the energy band from 0.2 eV up to 15 keV and a time resolution of less than 5ms with its Large Detector (LD) Array . It also has the provision for high-count rate measurements in the same energy band using a Fast Detector (FD), with a photon-counting time resolution of 80µs. Mechanically, the Large Detector Array of the WFI is composed of 4 identical Large Detectors quadrants. Each Large Detector quadrant consists of a 512 x 512 pixel DEPFET (depleted p-channel field effect transistor) sensor with dedicated read-out Front End Electronics (FEE). The FEE ASICs (Application-Specific Integrated Circuit) and the DEPFET sensor are linked through bond-wires. Both the DEPFET sensor and the FEE are supported using separate frames that are thermally decoupled to reduce the parasitic heat between them since DEPFET sensor operates at a much lower temperature compared to the FEE. The DEPFET sensor and the FEE PCB are both bonded to their frames using adhesives.
Two critical thermo-mechanical aspects of the design are identified: the stresses induced in adhesive bonds during cool-down to operating temperatures and stresses in the bond-wires due relative displacement between the DEPFET sensor and the FEE ASICs caused by their thermo-elastic deformation.
A single LD-quadrant is tested in a ‘'qualification-like’' manner by cycling it through the operational and non-operational temperatures to verify the above-mentioned aspects of design. The test is carried out at the in-house LUCHS test facility of the Max Planck Institute for Extraterrestrial Physics with a setup consisting of a small vacuum chamber, a Stirling cooler, heater power supply and control, and temperature measurement equipment. The presentation describes the test rationale, test environment and the success criteria. Further, the results of the test are presented and discussed.
