Screening of Flexible Cables by Nonlinear Resistance Measurements

摘要

Two traces in flexible cables used in the Milstar agile beam antenna systemfailed during acceptance testing. The cables, essentially printed circuit boards fabricated on flexible substrates, are composed of copper-foil conductors sandwiched between insulating Kapton layers. The cables carry current pulses used in the steering circuitry for the antenna beam. Upon sectioning and inspection of the suspect cables, substantial thinning of the copper foil conductors at feedthrough connections was noted. Other cables examined also exhibited thinning of metallization. Cables with degraded metallization develop anomalously high electrical resistances or can fail 'open'. The difficulties encountered with these cables resulted from poor workmanship, and the cable manufacturer subsequently lost certification from the Defense Electronics Supply Center. However, a large number of the cables had already been installed in satellites, and the reliability of the cables is critically important to mission success. A considerable effort was, therefore, mounted by the contractors, with the support of Aerospace, to assess the extent of the problem and determine whether a suitable screening procedure could be developed so that only selective, rather than total, replacement of the cables installed on the first Milstar satellite, DFS 1, might be necessary. In the course of this investigation, a screening test based on nonlinearities in cable resistance was developed. This test was originally intended to be applied to the cables in flight hardware. In fact, the application of this test to cables still in stores uncovered additional defective cables and led to a decision to replace all flexible cables with those from another manufacturer. Flexible cable, Nonlinear resistance.