Influence of ultrasounds on interfacial microstructures of Cu-Sn solder joints

Abstract

Purpose

This study aims to investigate the interfacial microstructures of ultrasonic-assisted solder joints at different soldering times.

Design/methodology/approach

Solder joints with different microstructures are obtained by ultrasonic-assisted soldering. To analyze the effect of ultrasounds on Cu₆Sn₅ growth during the solid–liquid reaction stage, the interconnection heights of solder joints are increased from 30 to 50 μm.

Findings

Scallop-like Cu₆Sn₅ nucleate and grow along the Cu₆Sn₅/Cu₃Sn interface under the traditional soldering process. By comparison, some Cu₆Sn₅ are formed at Cu₆Sn₅/Cu₃Sn interface and some Cu₆Sn₅ are randomly distributed in Sn when ultrasonic-assisted soldering process is used. The reason for the formation of non-interfacial Cu₆Sn₅ has to do with the shock waves and micro-jets produced by ultrasonic treatment, which leads to separation of some Cu₆Sn₅ from the interfacial Cu₆Sn₅ to form non-interfacial Cu₆Sn₅. The local high pressure generated by the ultrasounds promotes the heterogeneous nucleation and growth of Cu₆Sn₅. Also, some branch-like Cu₃Sn formed at Cu₆Sn₅/Cu₃Sn interface render the interfacial Cu₃Sn in ultrasonic-assisted solder joints present a different morphology from the wave-like or planar-like Cu₃Sn in conventional soldering joints. Meanwhile, some non-interfacial Cu₃Sn are present in non-interfacial Cu₆Sn₅ due to reaction of Cu atoms in liquid Sn with non-interfacial Cu₆Sn₅ to form non-interfacial Cu₃Sn. Overall, full Cu₃Sn solder joints are obtained at ultrasonic times of 60 s.

Originality/value

The obtained microstructure evolutions of ultrasonic-assisted solder joints in this paper are different from those reported in previous studies. Based on these differences, the effects of ultrasounds on the formation of non-interfacial IMCs and growth of interfacial IMCs are systematically analyzed by comparing with the traditional soldering process.

Citation

Han, X., Li, X., Yao, P. and Chen, D. (2021), "Influence of ultrasounds on interfacial microstructures of Cu-Sn solder joints", Soldering & Surface Mount Technology, Vol. 33 No. 4, pp. 206-214. https://doi.org/10.1108/SSMT-06-2020-0026