热迁移作用时小间隙Cu/Sn-58Bi/Cu焊点显微组织演变

Microstructure Evolution of Cu/Sn-58Bi/Cu Solder Joints with Small Gap during Thermomigration

研究了高度为10μm的Cu/Sn-58Bi/Cu微焊点在加载2 000℃/cm温度梯度以及125℃时效不同时间后的显微组织。结果表明,随着热迁移时间延长,Bi先粗化,然后向冷端偏聚,800h时焊点冷端形成几乎连续的Bi层,同时焊点界面金属间化合物(IMCs)呈对称生长,并且生长速率较慢。在时效条件下,焊点两端的界面IMCs向焊点中心快速生长,逐渐在焊点中心形成均匀且连续的Bi带,200h时Sn被消耗完毕。随着时效时间进一步延长,IMCs中Cu6Sn5逐渐转变为Cu3Sn。此外,热迁移条件下,焊点中的Bi可以抑制界面IMCs的不对称生长,并且降低界面IMCs的生长速率,这表明在钎料合金中加Bi可提高微焊点的服役可靠性。

The microstructure evolution of the Cu/Sn-58Bi/Cu solder joints with 10μm bump heiGHTunder a temperature gradient of 2 000℃/cm and aging at 125 ℃for different time were investigated,respectively.The results reveal that Bi phase is firstly coarsened and then segregated to the cold end with TM time increase,and then formed a nearly continuous Bi layer at the cold end after TM 800 h.Meanwhile,the intermetallic compounds(IMCs)are grown nearly symmetrically and slowly at the solder joint interface.However,during aging process,the interfacial IMCs are grown rapidly toward the center of the solder joint,resulting in a uniform and continuous Bi layer generation.After Sn phase is consumed completely at aging for 200 h,the Cu6Sn-5 in IMCs is gradually transformed to Cu3 Sn.By comparing the above experimental results,it is found that Bi phase in the solder joint can inhibit asymmetric growth and reduce the growth rate of the interfacial IMCs under TM condition,which reveal that the Bi addition in the solder alloy can improve the service reliability of micro solder joint.