【摘要】 利用SEM和EDS研究了Cu/Sn-58Bi/Cu焊点在电流密度为5×10³A/cm²,80℃条件下晶须和小丘的生长。通电540 h后,在焊点阴极界面区出现了钎料损耗,同时形成了晶须,而在阳极Cu基板的钎料薄膜上形成了大量弯曲状晶须和块状小丘。EDS检测表明,这些晶须和小丘为Sn和Bi的混合物。通电630 h后,阳极上的晶须和小丘数量明显增多,原来形成晶须的尺寸和形状没有变化,阴极界面处形成Cu₆Sn₅金属间化合物。上述现象表明:电迁移引发了金属原子的扩散迁移,从而在阳极Cu基板上形成了一层钎料薄膜。钎料薄膜中金属间化合物的形成导致压应力的产生,促使晶须和小丘生长,而阴极钎料损耗区域内晶须的形成与Joule热聚集有关。更多还原

【Abstract】 With the trends of higher integration and microminiaturization in electronic packaging, the sizes of the soldered joints are becoming smaller and smaller.The corresponding current density in the soldered joints can easily reach 10³A/cm² or higher,which makes the electromigration（EM） much more prominent.EM will lead to the atoms to pile up at the anode side and produce voids or cracks at the cathode side.Furthermore,with the stressing time increasing,these voids or cracks will propagate gradually resulting in the soldered joint rupture.EM may induce whisker growth resulting in the short circuit.All these defects can degrade the reliability of the soldered joints.In this paper,the effect of electric current（5×10³ A/cm²,80℃） on the whisker and hillock growth in Cu/Sn-58Bi/Cu soldered joint was investigated by SEM and EDS.It was found that after current stressing for 540 h,the solder at the cathode side is depleted and whiskers appear in the depleted zone,while solder film forms on the Cu substrate at the anode side and a large number of whiskers and hillocks appear on the film. EDS revealed that these whiskers and hillocks are mixtures of Sn and Bi.When the stressing time reached 630 h,more whiskers and hillocks form and more amounts of Cu₆Sn₅ intermetallics form at the interface of solder and cathode.The above facts indicated that the electromigration may induce diffusion and migration of metal atoms,leading to formation of a thin solder film on the anodic Cu substrate.The compressive stress generated by intermetallics formation provides a driving force for whisker and hillock growth on the solder film,and the Joule heating should be responsible for the whisker growth at the cathode side.There is no credible approach for predicting the whisker growth time,growth velocity and whisker length although several mechanisms have been proposed,but are not universally accepted.By general consensus,compressive stress is recognized as the main driving force for whisker growth and a break of the protective oxide on the surface.更多还原