| XIAO Jin,QU Fu-kang,CHENG Wei,LI Wu-chu.Interface between Sn-1.5Ag-2Zn Low Silver Lead-free Solder and Oriented Copper[J],52(8):406-412 |
| Interface between Sn-1.5Ag-2Zn Low Silver Lead-free Solder and Oriented Copper |
| Received:June 19, 2022 Revised:October 26, 2022 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.08.036 |
| KeyWord:Sn-1.5Ag-2Zn single crystal copper alloy solder welding diffusion |
| Author | Institution |
| XIAO Jin |
Guangzhou Huali College, Guangzhou , China |
| QU Fu-kang |
Guangzhou Huali College, Guangzhou , China |
| CHENG Wei |
Guangzhou Huali College, Guangzhou , China |
| LI Wu-chu |
Guangzhou Huali College, Guangzhou , China |
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| Abstract: |
| High density packaging technology reduces the pad size and the number of grains contained in the pad. When the polycrystalline pad turns into a single crystal pad, the grain orientation has an important impact on the formation of the intermetallic compounds at the interface. Sn-1.5Ag-2Zn, a promising solder alloy, was selected to study the interfacial reaction between solder and single crystal (111) copper substrate, and the growth kinetics of intermetallic was obtained. Sn-1.5Ag-2Zn lead-free solder was refluxed with single crystal (111) copper substrate and polycrystalline red copper substrate at 250 ℃ for 5 min, and the welded sample was heat-treated at 160 ℃ for 20 h, 100 h, 300 h and 600 h respectively. The microstructure, composition and properties of intermetallic at the welding interface were studied by Scanning Electron Microscope, Backscattered Electron Imaging, Secondary Electron Imaging, X-ray Diffraction (XRD) and Energy Dispersive Spectrometer. The uneven scallop like Cu6Sn5 intermetallic compound layer grew rapidly when the alloy solder contacted with the copper substrate. The Cu6Sn5 grain size formed on the surface of single crystal copper was larger than that of polycrystalline copper. Single crystal copper had no grain boundary to block atomic diffusion, which affected grain nucleation and growth. The growth rate of Cu6Sn5 formed by alloy solder and the single crystal (111) copper solder joint after heat treatment at 160 ℃ for 20 h was about twice that of the polycrystalline copper solder joint. Then, it grew slowly with the increase of heat treatment time. After 600 h of heat treatment, the thick layer of Cu6Sn5 broke due to crack diffusion, and the thickness of intermetallic compound remained at 3.5 µm. Cu5Zn8 generated at the solder and polycrystalline copper solder joint during heat treatment acted as a barrier layer, preventing the solder from contacting the copper substrate and inhibiting the formation of Cu6Sn5. After 300 h of heat treatment, Cu5Zn8 was broken and decomposed, and Cu6Sn5 grew rapidly after the barrier layer disappeared, with a thickness of about 2.8 µm. The thickness of intermetallic compound of solder joint on single crystal copper is 0.7 µm more than that on polycrystalline copper. After heat treatment, the intermetallic compound formed at the interface between alloy solder and single crystal copper has better compactness and basically no pores, while there are obvious pores between intermetallic compound grains at the interface between alloy solder and polycrystalline copper, which can predict that the welding quality of the interface between alloy solder and single crystal copper is better. |
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