Reliability optimisation for the multi-contact connector system under fretting conditions

The harsh operating environments of many electronic systems, such as in the automotive and aerospace applications, make the semi-permanent connector terminal susceptible to intermittent failure or high contact resistance. Fretting, small cyclic movements at the contact interface, is exacerbated by oxidation to cause fretting corrosion, resulting in these types of failures. However, due to the fretting action, the contact does not remain in the failed state but often recovers to low contact resistance for a period before the next failure event. Improvements in reliability can be achieved by specific design considerations, either increasing the normal force of the contacts, or increasing the number of contacts per terminal or both. This paper shows the optimum design for the ratio of the total normal force (F) of all contacts and the number of contacts (n) per terminal, for one of the most popular contact materials used in connector technology. A model is developed, the optimum F/n Model, incorporating failure and recovery rates based on a theoretical understanding of the contact interface and experimental investigations. This is used to select the appropriate ratio between normal force and number of contacts per terminal (force/multi-contact, F/n) ratio for optimised reliability. A minimum in the unreliability function is found for particular values of force and contact number and recommended for optimum performance for the tin-plated system.