摘要
CuSn合金是重要的无铅焊料。在焊接冷却过程中186~189℃温度区间,具有NiAs B81结构的η-Cu6Sn5会发生相变形成具有多种调制结构的η’-Cu6Sn5相。该相变机理至今尚未清楚阐明。本文使用扫描透射电子显微学方法对空气冷却的CuSn合金中的η-Cu6Sn5进行精细结构表征,观察到η-Cu6Sn5晶粒表面形成一层厚度约为2~3 nm的富Cu重构层η~S-Cu6Sn5。表面重构导致多余Cu原子和部分Sn原子占据2(d)空位,其结构不同于已发现的各种超结构。发现η-Cu6Sn5晶粒内部多余Cu原子随机占据2(d)空位,形成短程有序结构,傅里叶变换出现三次调制结构。研究表明该相变是由Cu原子沿表面或晶间扩散主导,这对进一步揭示η’相调制结构的形成和提高CuSn焊料电学性能与机械性能具有重要意义,为优化焊接流程和降低电迁移效应提供了基础研究的支撑。
CuSn-based alloy is an important candidate for lead-free solder.When the temperature decreases to 186-189℃after welding,the phase transition ofη-Cu6 Sn5 with NiAs B81 occurs and various superstructures ofη’-Cu6 Sn5 is formed.However,the mechanism that governs the transition is still has not been studied clearly.Here,using scanning transmission electron microscopy,we discovered the surface reconstruction inη-Cu6 Sn5 grains in Cu-(50 at.%)Sn alloy from air cooling.The copper-rich reconstructed surface layer ofηS-Cu6 Sn5 is about 2-3 nm thick,with extra Cu atoms and some Sn atoms filling 2(d)lattice positions.We also found that short range ordering structure formed in the grain,resulting in three-order super reflections in fast Fourier transform pattern.The research indicates thatη-η’phase transition is controlled by Cu diffusion along the surface and grain boundaries.The work provides insights on improving mechanical and electromigration properties of CuSn-based solder.
作者
崔文俊
江彬彬
胡执一
Van-TENDELOO Gustaaf
叶恒强
杜奎
桑夏晗
CUI Wen-jun;JIANG Bin-bin;HU Zhi-yi;Van-TENDELOO Gustaaf;YE Heng-qiang;DU Kui;SANG Xia-han(State Key Laboratory of Advanced Technology for Materials Synthesis and Processing,Wuhan Hubei 430070;Nanostructure Research Centre,Wuhan University of Technology,Wuhan Hubei 430070;Institute of Metal Research,Chinese Academy of Science,Shenyang Liaoning 110016,China;EMAT(Electron Microcopy for Materials Science),University of Antwerp,Antwerp Belgium)
出处
《电子显微学报》
CAS
CSCD
北大核心
2020年第5期513-519,共7页
Journal of Chinese Electron Microscopy Society
基金
国家自然科学基金资助项目(No.51902237)。