Ni/Au镀层与SnPb焊点界面电迁移的极性效应

Polarity of Electromigration at the Interface between SnPb Solder Joints and Ni/Au Finishes

采用Ni(P)/Au镀层-SnPb焊点-Ni(P)/Au镀层的互连结构,研究电迁移作用下焊点/镀层界面金属间化合物(IMC)的极性生长特性,从电位差和化学位梯度条件下原子定向扩散的角度分析互连结构的微结构变化的微观机制。在无外加应力条件下,由于液态反应速率远远快于固态反应速率,Ni(P)/Au镀层与焊点界面IMC经过120℃、100h的热处理后无明显变化。但是,在电迁移作用下,由于Sn沿电子流方向的定向扩散使阳极界面IMC异常生长,而阴极界面IMC厚度基本不变。由于电子由上层Cu布线进入焊点的电子注入口位于三相结合界面位置,在焦耳热的作用下会导致焊料的局部熔融,引起Cu布线与焊料的反应,使电子注入口的Cu布线合金化。

The polarity of electromigration at the interface between solder joints and finishes was studied with the interconnects structure of Ni（P）/Au finishes-SnPb solder joint-Ni（P）/Au finishes. The mechanism of microstructural evaluation of interconnects was investigated in terms of directional diffusion of atoms under electrical and chemical potential. The IMC layers on the interface between Ni（P）/Au finishes and solder joints have only a little change in thickness after the annealing of 120 ℃ for 100 h because the velocity of wetting reaction is faster than the solid state reaction. But under the condition of electromigration, the directional diffusion of Sn atoms along the electron flow direction induces the abnormal growth of IMC on the anode interface, and the restraint at cathode. The cathode contact is on the upside, where the electron current enters the solder bump, and locates at the triple point. The solder would melt at this point by Joule heating, resulting in the reaction between the Cu wire and solder.