关键词: SAC305 BGA 焊点, 电迁移, 电阻变化, 微观组织, 失效模式

Abstract: By real-time monitoring of the resistance change of SAC305 ball grid array (BGA) solder joints during electromigration (EM), and correlating it with the microstructural evolution of the solder joints, the EM failure modes of SAC305 BGA solder joints were revealed. For the No.1 solder joint, where the θ angle (the angle between the c-axis of the β-Sn grain and the electron flow direction) was as high as 67°, the self-diffusion of Sn atoms during EM led to void formation at the cathode interface of the joint. These voids gradually induced crack initiation and propagation, resulting in a slow but continuous increase in resistance. After 1 500 h of current stressing, the rate of change of resistance was only 8.72%; For the No.2 solder joint, which had a small θ angle of 23°, the directional migration of Cu atoms during EM caused extensive dissolution of the Cu under-bump metallization (UBM) at the cathode. The overall rate of change of resistance was relatively high; however, the resistance increased slowly during the early EM stage. Once the resistance increase reached approximately 15%, it rose sharply to 100%, leading to rapid failure.

Key words: SAC305 BGA solder joint, electromigration, resistance change, microstructure, failure mode