Accelerated tests to simulate metal migration in hybrid circuits

The dominant form of metal migration (i.e. Ag) in thick films, is composed of electrodissolution, ion transport and electrodeposition steps. Depending on the product type and its operating environment, some of these mechanisms are dominant and could alone be used to essentially model the metal migration in hybrid circuits. In this study, the dominant root cause for Ag migration was accelerated using coupon tests with dilute NaCl, which simulates the effect of contaminants on the board. It was demonstrated that these tests could be used as a rapid screening procedure for the various pastes. The coupon tests were also substantiated with results from the product test in the temperature, humidity, bias (THB) tests, which demonstrated the effect of Pd on Ag migration. Weibull curves obtained from the coupon and THB data demonstrated the product robustness. This was also determined by using the THB data and acceleration factors using field monitoring programs and those published in literature. The coupon and THB data were used to initiate changes in product design and manufacturing, thereby increasing product reliability.