Design and Validation of Corner Nonfunctional Solder Joint Canaries Using Damage Modeling and Four-Point Bending Tests

In this article, corner nonfunctional solder joints were designed as solder joint canaries, and their cycles to failure were compared under four-point bending and thermal cycling tests. A more efficient design and verification method for solder joint canaries was developed. By changing the PCB pad area of the corner solder joints, they were used as canaries for internal functional solder joints, allowing in-situ prediction of internal solder joint failures. To obtain the cycles to failure of solder joint canaries of different sizes, both thermal cycling tests and four-point bending cyclic tests were performed. The four-point bending test provides a more controllable and faster stress loading process. The results show that, compared with the four-point bending test, the thermal cycling test has a longer testing period and shows less distinct regulation effects among different-sized solder joint canaries. To verify the experimental results, a unified creep-plasticity constitutive model coupled with damage was proposed based on a previous model. Using the four-point bending simulation model, the damage evolution during solder joint fatigue was simulated, and the failure behaviors of different-sized solder joint canaries were validated. Further analysis shows that the initial R50 solder joints contain more low-angle grain boundaries and smaller orientation differences compared with the R100 solder joints, resulting in a longer fatigue life. These findings provide important theoretical and methodological support for the efficient design and verification of solder joint canaries.