The high- and low-stressed photodetector array camera and spectrometer (PACS) modules (linear 16-pixel arrays) are the basic constituents of the 16 × 25 pixel far-infrared (57–220 μm) PACS cameras aboard the Herschel satellite. The essentials for the stress application and the pixel stacking technique originate from detectors aboard the Infrared Space Observatory (ISO, 1995–1998) and for the field imaging far infrared line spectrometer (FIFI-LS) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). To meet the mass budget of the cameras and provide the required high tensile strength, the only usable material for the module body turned out to be an aluminum alloy (AL 7075 T651). Especially challenging was the tight thermal budget for the PACS modules. Compared to FIFI-LS, in the case of the PACS module the heat dissipation from the front end electronics (FEE) and harness substrates at about 4 K to the module body containing the pixel stack at about 2 K had to be reduced drastically. A genuine suspension concept and packaging for the respective substrates was developed and successfully applied, allowing reliable electrical wiring from the harness over the FEE on to the pixels. The FEE with the cryogenic readout electronics (CRE) is contributed by the Interuniversity Microelectronics Centre (IMEC).
The photodetector array camera and spectrometer (PACS) for the Herschel Space Observatory
