Effective ALT for Micro-Relay Reliability Assessment

Keyanna Qi April Aire

In the process of new product development or supplier management, it has always been a challenge to assess if a component meets the reliability requirement in a timely manner. Accelerated Life Test (ALT) can provide the statistical assurance that reliability goals are met or early warnings if they are not met. This paper describes in detail the case studies of the mechanical micro-relay reliability tests using accelerated life testing. In order to qualify the new component using accelerated life testing, it is very important to understand the operating conditions, the failure mode, and the cause of the failure under the current application conditions. The operating conditions should include the modes of operation (startup, shutdown, normal operation, any foreseeable overloads), load characteristic (static, repeated & reversed, fluctuating, shock or impact), and variations of loads over time. For the mechanical micro-relay, the relay life (cycles of operation) was characterized as function of operation current (two to eight times rated) and operation temperature, therefore, the two high current and higher temperature. The failure modes are “Stuck Open” where the mechanical switching element fails to close and the relay fails to carry a current, also see one “short” contact. The cross-section of the contacts shows damage (degradation) on the contact pat surface caused by the high inrush currents, high-sustained currents, and high voltage spikes. The life of a contact can be further degraded if contamination or pitting is present on the contact. This relay ALT saved testing time by up to 5 to 10 times with two stress variables (temperature and current), and the analysis of the ALT test results demonstrates that the relay under test meets the product reliability requirement.