Measurement and effects of high electrical current stress in solder joints

Damage mechanics of solder interconnects under high electrical current stress is an important reliability issue for next generation power electronic packaging as well as for future IC packaging, and may well be the dominant issue. Understanding the strain evolution in the solder over time is an important step toward developing the damage mechanics model. The real-time displacement evolution of eutectic SnPb solder in the solder joint under electrical current stressing was measured with Moiré Interferometry. For the first time the strain distribution in a solder joint under such stressing is reported. A comparison of measured strain with finite element (FE) simulation for pure thermal stressing was performed. The initial results show that the measured strain was largely due to electrical current. However, the current density in the solder joint was only 175 Amps/cm². This indicates the strain was developed in the solder at a current density considerably lower than that to invoke electromigration, and consequently, raises a strong reliability concern for solder joints exposed to relatively low current densities.