Effect of Trace Zn Addition on Interfacial Evolution in Sn-10Bi/Cu Solder Joints during Aging Condition.

Qingfeng Wang,Fengjiang Wang,Hong Chen

doi:10.3390/ma12244240

Abstract

Excessive growth of intermetallic compounds (IMCs) during service affects the reliability of solder joints, so how to suppress the growth of IMC thickness at the interface in solder joints becomes a widespread concern. In this work, the interfacial reaction between Sn-10Bi solder and Cu substrate after thermal aging was investigated. Moreover, to depress the IMC growth at the interface, trace amounts of Zn was added into the Sn-10Bi solder, and the interfacial reactions of Sn-10Bi-xZn solders (x = 0.2, 0.5) and Cu substrate after thermal aging were studied in this paper. Compounds such as Cu6(Sn, Zn)5 and Cu5Zn8 were formed at the interface after adding trace amounts of Zn. The addition of 0.2 and 0.5 wt% Zn significantly inhibited the thickness growth of IMCs and the formation of Cu3Sn IMC at the interface of Sn-10Bi-0.2Zn/Cu and Sn-10Bi-0.5Zn/Cu during thermal aging. Therefore, the addition of trace Zn had an obvious effect on the interfacial reaction of Sn-10Bi/Cu solder joint. Interestingly, the evolution of IMC thickness in Sn-10Bi-0.5Zn/Cu solder joints was completely different from that in Sn-10Bi or Sn-10Bi-0.2Zn solder joints, in which the spalling of IMCs occurred. In order to explore the mechanisms on the depressing effect from the addition of trace Zn, the activation energy Q in solder joints during aging was calculated.

Highlights

Due to the harmfulness of Pb to the human body and environment, Pb-free solders received an increasing attention in research and application in packaging in recent years [1,2]
Wang et al [9] investigated the interfacial behavior in Sn-Bi solid solution solder on Cu and found that Sn-Bi solder with low Bi content presented lower growth of intermetallic compound (IMC) thickness and higher joint strength compared with pure Sn solder
The compositions of interfacial IMCs in Sn-10Bi/Cu joints are Cu6 Sn5 and Cu3 Sn during isothermal aging. It can be seen from the line scan at the interface in Figure 5a,b that Cu atoms are mainly presented in Cu substrate and IMC layer, and Sn atoms are mainly presented inside the solder matrix and IMC layer

Summary

Introduction

Due to the harmfulness of Pb to the human body and environment, Pb-free solders received an increasing attention in research and application in packaging in recent years [1,2]. Sn-Bi solder is one of them due to its low melting point (139 ◦ C) and good mechanical properties [5]. Large amounts of Bi in Sn-58Bi eutectic increases the brittleness of the solder alloy because of the brittleness nature of Bi phases [6]. Sn-Bi solders with lower Bi content, especially Sn-Bi solid solution solders provide potential application to replace Sn-Ag-Cu series solders due to their similar melting point [7,8]. Wang et al [9] investigated the interfacial behavior in Sn-Bi solid solution solder on Cu and found that Sn-Bi solder with low Bi content presented lower growth of intermetallic compound (IMC) thickness and higher joint strength compared with pure Sn solder. Lai et al [11,12] compared Sn-10Bi solder with Sn-Ag-Cu

Methods

Results

Discussion

Conclusion