Microstructure and shear properties of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints under thermal cycling

Jianguo Cui,Keke Zhang,Di Zhao,Yibo Pan

doi:10.1038/s41598-021-85685-6

Abstract

Through ultrasonic wave assisted Sn2.5Ag0.7Cu0.1RExNi/Cu (x = 0, 0.05, 0.1) soldering test and − 40 to 125 °C thermal shock test, the microstructure and shear properties of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints under thermal cycling were studied by the SEM, EDS and XRD. The results show that the Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints with high quality and high reliability can be obtained by ultrasonic assistance. When the ultrasonic vibration power is 88 W, the ultrasonic-assisted Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu solder joints exhibits the optimized performance. During the thermal cycling process, the shear strength of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had a linear relationship with the thickness of interfacial intermetallic compound (IMC). Under the thermal cycling, the interfacial IMC layer of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints consisted of (Cu,Ni)6Sn5 and Cu3Sn. The thickness of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints was linearly related to the square root of equivalent time. The growth of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had an incubation period, and the growth of IMC was slow within 300 cycles. And after 300 cycles, the IMC grew rapidly, the granular IMC began to merge, and the thickness and roughness of IMC increased obviously, which led to a sharp decrease in the shear strength of the solder joints. The 0.05 wt% Ni could inhibit the excessive growth of IMC, improve the shear strength of solder joints and improve the reliability of solder joints. The fracture mechanism of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints changed from the ductile–brittle mixed fracture in the solder/IMC transition zone to the brittle fracture in the interfacial IMC.

Highlights

Today, with the rapid development of electronic information technology and the enhancement of people’s sense of environmental protection, various electronic devices are developing to integrated modules, and the internal solder joints are becoming denser, which raises higher requirements for the quality and reliability of solder joints
When the ultrasonic vibration power is 88 W, the ultrasonic-assisted Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu solder joints exhibits the optimized performance, which was consistent with the previous studies[6,14]
For intermetallic compound (IMC), with Ni additions, the K of interfacial IMC layer decreased. It indicated that the growth rate of interfacial IMC of the solder joints with Ni grew slower than that of the monolithic Sn2.5Ag0.7Cu0.1RE/Cu solder joints under all conditions.The results showed that the addition of an appropriate amount of Ni could inhibit the excessive growth of IMC, this result was consistent with the above analysis

Summary

Introduction

With the rapid development of electronic information technology and the enhancement of people’s sense of environmental protection, various electronic devices are developing to integrated modules, and the internal solder joints are becoming denser, which raises higher requirements for the quality and reliability of solder joints. It is necessary to develop a new method to improve the solder quality and the solder joints reliability under halogen-free conditions. Ji et al.[17] investigated the effect of the ultrasonic vibration on the microstructure and properties of lead-free solder joints, which showed that the solder joints possessed a refined microstructure. In this study, we investigated the characteristics of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu lead-free solder joints under thermal cycling. It reveals the effect of thermal cycling on the morphology of the interfacial IMC and shear properties of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu (x = 0, 0.05, 0.1) solder joints in terms of the IMC sizes, shear strength and fracture morphology, and provides a new way for the development of high reliability soldering under harsh conditions of service

Methods

Results

Conclusion