Nucleation and Morphology of Cu6Sn5 Intermetallic at the Interface between Molten Sn-0.7Cu-0.2Cr Solder and Cu Substrate

Junhyuk Son,Dong-Jin Byun,Min-Su Kim,Yong-Ho Ko,Junghwan Bang,Dong-Yurl Yu

doi:10.3390/met11020210

Abstract

The nucleation kinetics and morphology of Cu6Sn5 IMCs at the interface between a Sn-0.7Cu-0.2Cr solder and Cu substrate were investigated in this study. A Sn-0.7Cu solder was utilized as a reference to elucidate the impact of Cr addition. The mechanical properties of the solder joints were determined via ball-shear tests. Cu coupons were dipped in the molten solders for 1 and 3 s at 240–300 °C, and the morphological analyses were conducted via electron microscopy. Both the solders contained scallop-like Cu6Sn5 IMCs. The smallest Cu6Sn5 IMCs were observed at 260 °C in both the solders, and the particle size increased at 280 and 300 °C. The IMCs in the Sn-0.7Cu-0.2Cr solder were smaller and thinner than those in the Sn-0.7Cu solder at all the reaction temperatures. The thickness of the IMCs increased as the reaction temperature increased. Inverse C-type nucleation curves were obtained, and the maximum nucleation rate was observed at an intermediate temperature. The shear strengths of the Sn-0.7Cu-0.2Cr solder joints were higher than those of the Sn-0.7Cu solder joints. This study will facilitate the application of lead-free solders, such as Sn-0.7Cu-0.2Cr, in automotive electrical components.

Highlights

Lead-free solders are utilized as the joint materials in automotive electrical components to comply with environmental regulations such as end-of-life vehicles (ELVs) and restriction of hazardous substances (RoHS) directives [1,2]
The Cu6Sn5 intermetallic compound (IMC) were small and thin at the low reaction temperatures owing to the high nucleation rate
The size and thickness of the Cu6Sn5 IMCs increased as the temperature increased owing to the increase in the nucleus growth rate [24]

Summary

Introduction

Lead-free solders are utilized as the joint materials in automotive electrical components to comply with environmental regulations such as end-of-life vehicles (ELVs) and restriction of hazardous substances (RoHS) directives [1,2]. The liquidsolid-state diffusion is initiated between the Sn of the molten solder and the Cu substrate in the ramping step. The Cu atoms are locally precipitated on top of the existing Cu6Sn5 IMC interface owing to their low-energy state in the cooling step [5,6,7,8]. The reliability of automotive electrical components under high temperature, high humidity, and combined vibrations should be higher than that of other components To address this challenge, the use of Sn-Ag-Cu, Sn-Ag, Sn-Au, Sn-Zn, and Sn-Cu solders as joint materials have been studied extensively. Several researchers have attempted to address this limitation by adding a low quantity of metals (e.g., Ni, Ag, Al, Co, or Cr) to the solder They investigated the microstructure and mechanical properties of the solder. The shear strengths of the Sn-0.7Cu-0.2Cr solder joints were higher than those of the Sn-0.7Cu solder joints

Methods

Results

Conclusion