Compact 3D packaging of a photodetector array camera and spectrometer

CEA/DSM/DAPNIA/ Service d´Astrophysique in Saclay and CEA/DRT/LETI in Grenoble have been developing filled Bolometer arrays, sensitive in far infrared and submillimeter, since 1997. These arrays are based on an all Silicon technology development, and made of a Silicon grid held onto a substrate using very thin Silicon beam. Currently we are developing a Photodetector Array Camera and Spectrometer (PACS) for spatial observations that will be launched by the Herschel satellite. In this project, we are facing an extremely harsh environment with high thermal and mechanical constraints. The detector package must thermally insulate different temperature levels, assure a very high interconnection efficiency, protect from the high photon background environment, while remaining compact and light. To create one detector we use eight 16×18 pixels arrays with a 750 μm pitch, which are positioned next to each other and hybridized onto readout circuits. This assembly is connected onto buffer circuits using flexes made of Constantan wires imbedded into Kapton (polyimide). Because of the large amount of connections (over 800) we use a collective method with Indium pads to hybridize the flexes onto the readout circuits. We are able to fold the system together and place it in an isolating cavity. Here we are describing this assembly in details as well as giving some qualification results regarding vibration and shock.