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Gamma-ray Large Area Space Telescope. Kapton bias circuits delaminations Alessandro Brez INFN - Pisa Brez@pi.infn.it. The problem.
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Gamma-ray Large Area Space Telescope Kapton bias circuits delaminations Alessandro Brez INFN - Pisa Brez@pi.infn.it
The problem • Several trays show a delamination of the Kapton bias circuit in the peripheral area, up to the shield Cu plane. The shielding plane stays covered by the upper Kapton layer. • we had a first isolated case (tray MID093, back side, bias s/n 4606), i.e. 1 failure over 317 cases between SN/4000 and SN/4699 • batch with SNs/4700-4899 show much higher rate of defective bias circuits (9/47 glued to trays) • current batch (SNs 49xx) has not been used yet
Test Method Kapton layers Cu shield plane double tape Al base The bias circuit is attached to an Al plane with a double adhesive tape A corner of the bias circuit is cut out with a scalpel The adhesion of the 2 Katpon layers is qualitatively tested with the scalpel edge , trying to remove the upper layer, simulating the trimming operation
Test results from Bias circuit #4504 Good Bias circuit: Working hard with the scalpel it was possible to delaminate only very small flaps of the upper Kapton layer. The adhesion of the 2 layers is higher than the adhesion to the tape. Cu Kapton+Kapton Cu tape
Test results from Bias circuit #4759 Bad Bias circuit from batch with some problem (SNs/4700-4899): Working with the scalpel it was possible to delaminate flaps of few mm size of the upper Kapton layer. The adhesion of the 2 layers is smaller than the adhesion to the tape. Flaps
Test results from Bias circuit #4969 Bad Bias circuit from current batch: Working with the scalpel it was possible to delaminate flaps of several mm size of the upper Kapton layer. The delamination stops at the Cu layer: very similar to the defective trays. The adhesion of the 2 layers is very poor: when the edge of the scalpel in inserted between the layers, the delamination propagates by itself.
Conclusion • We cannot use Bias circuits with S/N > 4700 • We ask urgent production of new bias circuits – we can cover up to tower 7 tray production with other bias circuits currently in Plyform • We will send back the whole batches 47xx and 49xx for test