Improved physical understanding of intermittent failure in continuous monitoring method

Accelerated reliability tests are used to evaluate product life and to ensure a good fit with mission profile. Adequate detecting failure methods and criteria are fundamental to ensure the validity of the test results. In electronic interconnect reliability tests, several types of in-situ electrical continuity methods or manual resistance measurements with crack length analyses are used as failure indicator. Continuous monitoring at high sampling rate shows intermittent signals before permanent failure. In this paper we present a new test approach to improving physical understanding of these intermittent failures. Two different test benches are used to monitor BGA component solder joints under stress. Cross-section analysis, electrical circuit models and signal analysis are used to highlight the relationship between crack propagation and electrical continuity. Finally, basic electric contact theory is applied to explain resistance value fluctuations before permanent failure. The results suggest that high sampling rate in-situ monitoring methods have to be used in order to have an appropriate failure criterion and consequently be more representative of reliability results for electronic interconnects in the field.