Comparison of Fatigue Crack Initiation/Propagation and Daisy-Chain Resistance in Lead-Free Solder Joints Under Temperature Cycling Test

It has been a common practice in the microelectronics industry to evaluate the long-term solder joint reliability using the accelerated temperature cycling (ATC) test. The thermal fatigue failure mechanism of solder joints during the ATC test involves the initiation of microcracks and, subsequently, their propagation and coalescence for a complete joint separation. Traditionally, the industry employs methods based on the measurement of the daisy-chain resistance to monitor the failure of the solder joints. Yet, there is no specific study to investigate the relationship between the resistance change during the ATC test and the crack formation of the solder fatigue. This study aims to provide an experimental investigation on such relationship. A custom-made sample is designed and fabricated in the study. The fatigue crack growth in solder joints of certain custom-made assemblies can be directly inspected during the test. The daisy-chain resistance is real-time monitored. The test results reveal that the electrical resistance monitoring approach is not effective in detecting the fatigue crack initiation and subsequent propagation. As a result, a partially degraded interconnect cannot be identified. Therefore, new monitoring methods should be developed for this purpose.