Contact resistance comparison of good and bad crimp joints with tinned wires under thermal shock

#16 wire gauge crimp joints of good quality were made tinned wires in the conventional way. Some of them then subjected to twisting in gap between the two wings. All of them were heat-soaked at 135/spl deg/C for 300 hours. They were then into a thermal-shock furnace for thermal cycling from -40/spl deg/C to 125/spl deg/C, each cycle lasting one hour for a total of 570hours. The four-leads method was used to measure the contact resistance for every cycle under the dry circuit condition. The contact resistance of good crimps generally increased at a slower pace over time than the bad ones. The resistance of some good and bad crimps would tend to more or less off after 100-200 cycles while others would continue to increase their resistance without leveling off and some of them might show a sudden jump. Nevertheless, the measured resistance history showed that a crimp with a tinned wire exhibited accepted performance whether it was good or not so good a crimp. The results also showed that the temperature history would effect the contact resistance measured at a later time. For example, the resistance of a crimp at 125/spl deg/C would be somehow different depending on weather the previous temperature started from -40/spl deg/C or from -17/spl deg/C. Data analysis showed that even with severe thermal shocks for 570 hours and possible consequence of repeated shearing, the contact in the crimp was still essentially a metallic one.