利用同步辐射实时成像技术原位研究了Cu/Sn-37Pb/Cu微焊点在185 ℃、1×10⁴ A/cm²电流密度条件下液-固电迁移过程中Pb原子的扩散迁移行为及其析出机制。在微焊点加热熔化阶段，Pb原子向阳极定向迁移并聚集形成富Pb相，其厚度随时间的延长而增大；在保温阶段，阳极的富Pb相部分溶解，Pb原子反向扩散至阴极，最终钎料内部形成两相平衡组织；在冷却凝固阶段，Pb原子再次向阳极定向迁移，直至凝固，最终钎料内部形成三相组织：富Pb相、Sn-Pb相和富Sn相。基于加热阶段富Pb相的生长动力学，计算获得Pb原子在185 ℃下的有效电荷数(Z^*)为-3.20，为Pb原子的电迁移方向提供了判断依据。Pb原子在电迁移中的反常迁移行为归因于电迁移通量(J_em)与化学势通量(J_chem)的竞争机制。

Electromigration (EM), which describes the mass transport due to momentum exchange between conducting electrons and diffusing metal atoms under an applied electric field, has become a serious reliability issue in high-density packaging. With the increasing demands for miniaturization, liquid-solid (L-S) EM will pose a critical challenge to the reliability of solder interconnects. In this work, synchrotron radiation real-time imaging technology is used to in situ study the interfacial reaction and atom migration in Cu/Sn-37Pb/Cu solder interconnects undergoing L-S EM at 185 ℃ with a current density of 1.0×10⁴ A/cm². In the heating stage, Pb atoms directionally migrate from the cathode toward the anode, resulting in the growth of Pb-rich phase at the anode. In the dwelling stage, Pb atoms diffuse backward, then equilibrium phase is obtained. In the cooling stage, Pb atoms directionally migrate from the cathode toward the anode again until the solder solidified, three phases is obtained: the Pb-rich phase, the Sn-Pb phase and the Sn-rich phase. The abnormal migration behavior of Pb atoms in different stages is determined by the combined effect of the chemical potential gradient flux (J_chem) and EM-induced flux (J_em). J_em is determined by the effective charge number (Z^*) of Pb atoms, which was calculated to be -3.20 at 185 ℃ based on the growth kinetics of the Pb-rich layer model.