Last year we performed what is called so called highly accelerated life testing (HALT) and during these tests it turned out that even though the setup is only taken to 125°C for 2000 hours, there was a failure on the pigtails that were connected to some of the Sunsensors.

The root cause of this failure was a mystery until today.

In advance of the HALT test we irradiated 6 diodes with 4 10^14 1MeV electrons (equivalent to 9.4Mrad)

Because we are preparing for additional radiation tests taking the diodes up to 8.10^14 1MeV electrons (18.8Mrad) we needed 6 pigtails again and tried to locate the pigtails we used earlier.

As it turns out all six pigtails we used for the radiation testing show a brittle fracture in the PTFE insulation.

This is too much of a coincidence to be without correlation so we looked up the radiation tolerance of standard PTFE wiring and found that the wires should not be used beyond 8Mrad.

Mystery solved.

The PTFE will not break away when not moved, but when moved will shatter and form kind of a confetti of PTFE slithers.

At least now we know why the wiring failed during the HALT testing and are reassured that selecting ECSS-3901-019 wiring for the BiSon64-ET (specified up to 40Mrad) was a good decision.

This example goes to show that ensuring radiation hardness has many aspects.