激光喷射钎料球键合焊点界面组织及其可靠性分析

来源期刊：金属学报2010年第9期

论文作者：王晓林 李明雨 王春青

文章页码：1115 - 1120

关键词：激光喷射钎料球键合； 界面组织； 冷热循环； Sn-Ag-Cu钎料

Key words：laser jet solder ball bonding(LJSBB)； interfacial microstructure； thermal cycle test； Sn-Ag-Cu solder

摘    要：采用激光喷射钎料球键合技术以及Sn3.0Ag0.5Cu(质量分数,%)无Pb钎料球对厚Au焊盘进行了键合实验.采用SEM和EDS对焊点界面的微观组织进行了分析.采用冷热循环处理研究了焊点微观组织的演变及其对接头强度的影响.结果表明,由于钎焊过程的热量有限,导致焊盘上的Au层不能全部溶解到钎料中去,界面处形成Au+AuSn+AuSn₂+AuSn₄多层结构,其中AuSn₄呈指向钎料内部的针状.经过100 cyc以上冷热循环处理,界面处针状AuSn₄层平坦化,而残余Au通过固相扩散全部消耗,并在界面处形成(Au,Ni,Cu,Sn)四元相,导致焊点强度弱化.

Abstract: Laser jet solder ball bonding (LJSBB) technology is a special soldering method developed in cooperation by Fraunhofer Ltd and PacTech Ltd in 1998 to fulfill the specific needs in the packaging of micro-electro-mechanical system (MEMS) and other functional micro-devices.However, the metallurgy characteristics and reliability of the solder joint produced by LJSBB has not been broadly reported.In the present paper,the commonly used Au/Ni/Cu soldering pads were bonded by LJSBB with Sn3.0Ag0.5Cu lead free solder.The effect of laser energy on the interfacial microstructure of solder joint was investigated by SEM and EDS.The reliability of solder joints was also evaluated by thermal cycle treatment and strength test.Results show that due to the limited heat provided by laser beam,the Au layer of the commonly used Au/Ni/Cu soldering pad cannot completely dissolve into solder during LJSBB process,which leads to the formation of multilayered reactive structure of Au+AuSn+AuSn₂+AuSn₄ in the interface of solder joint.The AuSn₄ locates at the most outside of the reactive structure and presents a needle-like shape.In despite of the brittle nature of Au-Sn intermetallics,the as-soldered joints present a comparatively high strength.However,the strength of solder joint decreases significantly after 100 thermal cycle treatment and keeps nearly unchanged after even more thermal cycle treatment.Metallurgy analysis of joint interface reveals that the thermal cycle treatment plays the roles of promoting the dissipation of residual Au in joint interface through solid state inter-diffusion,and leading to the formation of a quaternary phase of (Au,Ni,Cu,Sn) in interface,which results in weakening of LJSBB solder joint.