The influence of solder fillet geometry on the occurrence of corona discharge during operation between 400 and 900 V in partial vacuum

A number of experiments have been made to study the effect that different solder joint designs have on the voltage needed to initiate the onset of corona discharge under low ambient pressures. Wires were joined to both printed circuit board terminations and to electrical feedthroughs. All were constructed from materials known to be suitable for spacecraft. The main factor that determines whether solder joints will be prone to initiate corona discharges or electrical breakdown in a space environment is the actual minimum distance between terminals. Large, rounded solder fillets are desirable, but those containing protrusions or contours around wire strands have little adverse effect. It is shown that it is not always necessary, as is usually required by workmanship specifications related to high voltage connections, for operators to rework solder joints in order to achieve protrusion-free fillets. It would appear from metallurgical analyses of solder joints that it is the tin-rich phase that is sputtered from the fillet's surface during the phenomenon of corona discharge.