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This work investigates the influence on the partial discharge (PD) onset due to the geometry of solder fillets of aerospace and spacecraft component assemblies operating in vacuum and at high voltages. An automatic measuring system has been developed and calibrated to detect PD signals in vacuum (proportional to the apparent charge) which are recorded and displayed in terms of amplitude and temporal distributions. The experimental part of the project is aimed at investigating the influence of the geometry of solder fillets (produced according to the European space industry standard, ECSS-Q-70-08), on the occurrence of PD activity. Stranded terminals of high voltage cables were soldered to circular copper pads on FR4 fiberglass epoxy printed circuit board (PCB). Various copper electrode configurations have been produced and, prior to the test program, they were characterized for dimensional, electrical and optical properties. Two types of solder fillet geometries have been realized for each electrode configuration: round joints with an abundance of solder and sharp pointed joints made with minimal solder. The minimum distance between electrodes for all samples is nominally 5 mm. Paschen-like curves were established from measurements performed where the product of pressure x distance lies in the range of 2 mbar mm-50 mbar mm. Corona inception voltage (CIV) and corona extinction voltage (CEV) values were recorded at different values of pressure x distance. Stable glow discharge triggering voltage and current were also measured. The experimental results indicated that the PD activity for the sharp pointed pads and sharp pointed joints is greater than the other cases, but no significant differences (less than 50 V) of the values of CIV and CEV have been found.Index Terms-High voltage systems, partial discharges, printed circuit board, solder fillets.

The filamentary growths of single crystals on material surfaces are termed whiskers. They are seen to nucleate and grow on certain electronic materials either from vapour and liquid phases or by a process induced by residual stresses in electroplated surfaces. Whisker growth does not depend on the existence of an electric field and surfaces prone to their growth may nucleate and form whiskers as a result of exposure to a space environment. This paper includes a detailed examination of tin whiskers which were found to have 1 to 4 micron diameters and lengths exceeding 2 mm. Some were found to carry currents between 22 and 32 mA before burning out. Conductive whiskers can cause extensive short circuit damage to spacecraft electronics particularly as miniature devices progressively employ closer spacings between conductors. Several modes of whisker growth on spacecraft electronic materials (molybdenum, tungsten, Kovar, tin) have been observed and are described. Tin, cadmium and zinc surfaces can support stress‐induced whisker growth and it is recommended that these metal finishes are excluded from spacecraft design and possibly replaced by a tin‐lead alloy.