镀银的铜引线与PCB焊盘平行微隙焊时的界面行为
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摘要
研究了平行微隙焊过程中镀银的铜引线分别与PCB板上的裸铜焊盘及镀锡铜焊盘的接头特性.结果表明,对于Ag/Cu接头,接头的界面处两侧的Cu向中间的Ag处扩散较多.对于Ag/Sn/Cu接头,由于界面处Sn的分布受两侧的Cu向中间的Ag处扩散的影响,造成了Sn在界面处顶部和底部含量较高,中间含量低的分布.虽然Sn膜很薄,但是Sn的局部熔化导致了引线周围裂纹的产生,对接头的强度影响很大.Ag/Sn/Cu接头的拉伸强度低于Ag/Cu接头.因此利用平行微隙焊将镀银引线焊接到PCB板上时,建议采用裸铜焊盘而尽量不要采用镀锡焊盘.
Interfacial behavior between Ag-plated copper wire and Cu pads as well as Sn coated Cu pads on PCB( printed circuit board) were studied respectively during parallel micro gap welding process. Results show that Cu in the two sides of interfacial layer diffuses into Ag layer significantly at the interfaces of Ag/Cu joint. For Ag/Sn/Cu joint,the Sn distribution is influenced by Cu that diffuses into the Ag layer. Therefore,Sn concentration is higher at the top and the bottom of interface,but lower in the middle of interface. Although the Sn layer is very thin,it induces crack generation around the Ag-plated copper wire and decreases the bonding strength. The bonding strength of Ag/Sn/Cu joint is lower than that of Ag/Cu joint. For Ag-plated copper wires,the Cu pads are better for parallel micro gap welding rather than the Sn coated Cu pads on PCB.
Interfacial behavior between Ag-plated copper wire and Cu pads as well as Sn coated Cu pads on PCB( printed circuit board) were studied respectively during parallel micro gap welding process. Results show that Cu in the two sides of interfacial layer diffuses into Ag layer significantly at the interfaces of Ag/Cu joint. For Ag/Sn/Cu joint,the Sn distribution is influenced by Cu that diffuses into the Ag layer. Therefore,Sn concentration is higher at the top and the bottom of interface,but lower in the middle of interface. Although the Sn layer is very thin,it induces crack generation around the Ag-plated copper wire and decreases the bonding strength. The bonding strength of Ag/Sn/Cu joint is lower than that of Ag/Cu joint. For Ag-plated copper wires,the Cu pads are better for parallel micro gap welding rather than the Sn coated Cu pads on PCB.
引文
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[2]Abew M,Selvaduray G.Lead-free solders inmicroelectronics[J].Materials Science and Engineering:R,2000,27(5):95-141.
[3]Lee J H,Lee Y H,Kim Y S.Fluxless laser reflow bumping of SnPb eutectuic soldering[J].Scripta Materialia,2000,42(8):789-793.
[4]Liu C,Hutt D A.Fluxless soldering of copper substrates using self-assembled monolayers for preservation[J].IEEE Trans on Comp.and Pack.Technol.,2006,29(3):512-521.
[5]Dong S J,Kelkar G P,Zhou Y.Electrode sticking during microresistance welding of thin metal sheets[J].IEEE Trans on Elect.Pack.Manuf.,2002,25(4):355-361.
[6]王晨曦,王春青,孔令超.Ni/Ni Cr平行微隙焊接接头的形成机理[J].焊接学报,2004,25(4):99-102.Wang Chenxi,Wang Chunqing,Kong Lingchao.Mechanism of Ni/Ni Cr joint formation by parallel micro gap welding[J].Transactions of the China Welding Institution,2004,25(4):99-102.
[7]Fukumoto S,Chen Z,Zhou Y.Interfacial phenomena and joint strength in resistance microwelding of crossed Au-plated Ni wires[J].Metallurgical and Materials Transactions A,2005,36A:2717-2724.
[8]孟亮,陈燕俊,刘茂森,等.扩散处理对Ag-Cu复合板界面区组织与成分的影响[J].金属学报,2001,37(1):47-51.Meng Liang,Chen Yanjun,Liu Maosen,et al.Effect of diffusion annealing on microstructure and composition distribution in interfacial regions of sliver-copper bimetallic sheets[J].Acta Metallurgica Sinica,2001,37(1):47-51.
[9]Feng W F,Wang C Q,Morinaga M.Electronic structure mechanism for the wettability of Sn-based solder alloys[J].Journal of Electronic Materials,2002,31(3):185-190.