Environmental-stress screening of space-qualified printed circuit boards

Two separate statistically designed experiments were performed in order to determine the long-term degradation of solder joints in two space-qualified board technologies: wire-wrap and stitch-weld boards. In the first experiment, extensive temperature cycling (1024 cycles) at a temperature change rate of 20°C/min showed that the solder contacts between the pins and board planes are more reliable on stitch-weld boards than on wire-wrap boards. In the second experiment, the effects of changing the environmental stress-screening (ESS) parameters pertinent to temperature cycling (i.e. the temperature range, the rate of temperature change, and the number of temperature cycles) were studied using the degradation of contact resistance in soldered and unsoldered connections in stitch-weld boards. The results showed that (1) soldered joints are more reliable than pins that are press-fitted into plated-through holes, (2) a wide range of temperature change or a high rate of temperature change degrades soldered or press-fit joints in stitch-weld boards, and (3) there are no differences of engineering significance due to the effect of the position of the solder joint relative to the head or collar of the stitch-weld pin. It is also shown that the effect of the rate of temperature change in ESS decreases while the effect of temperature range increases as the number of temperature cycles increases. In this experiment, the effects of temperature range began to dominate the effects of rate of temperature change after approximately 100 cycles