The interconnection technique to realize the detection planes have been defined through numerous tests, in collaboration with the firm Mipot (Cormons, Italy), using both "mechanical" and "real" silicon detectors. As a first step, the printed circuit boards are fixed to the corresponding tungsten plates. The detectors are glued, in rows of 3, on a specially designed 75 mm thick silicon detectors). thick kapton layer with a siliconic glue. Then, the wire bonding of the corresponding strips on each detector is performed. Afterwards, 3 such rows are glued on the supporting printed circuit board, again by using a special siliconic glue, to form the 3x3 silicon detector matrix of one view (either X or Y).
The silicon detectors for the PAMELA calorimeter are very large area devices (8 x 8 cm2 each), 380 mm thick and segmented into 32 strips with a pitch of 2.4 mm. They feature an innovative bias technique, adopted in order to bring the bias voltage with a wire bonding directly on the junction side of the devices. To accomplish that, the bulk contact is realised via a forward biased p+ implant running at the edge of the device. In this way, we can avoid the use of a conductive epoxy glue for gluing the detectors on the PCB, therefore preserving the devices from the large mechanical stress that these type of glues can induce during polymerization.
Several pre-series detectors, from two manufacturers, have been completely characterised in the laboratory. The test results are very good: the average value of strip leakage current is about 400 pA, which corresponds to an average current per unit area of 0.17 nA/cm2. Figure 3 shows the result (for one strip) of an I-V measurement performed over 72 hours on a pre-series detector. As one can see, the stability of the current, which is a crucial item in space applications, is excellent.
