分步法电镀制备的Au-Sn共晶凸点的微观组织

研究金属离子与络合剂摩尔浓度比、pH值及电镀温度对Au、Sn镀层表面形貌及其镀速的影响。通过分步法电镀Au/Sn/Au三层结构薄膜,并回流制备Au-Sn共晶凸点。结果表明:镀Au过程中,随着Au离子与亚硫酸钠摩尔浓度比的增加,Au镀层晶粒细化,并在摩尔浓度比为1:6时获得了最快的沉积速度;当电镀温度较低时,镀Au层表面呈多孔状,随着温度的升高,镀层致密性增加,晶粒也趋于圆滑。镀Sn过程中,随着Sn离子与焦磷酸钾摩尔浓度比的增大,镀层表面起伏加剧,镀层孔洞增多。当pH值为8.0时,镀层平整致密,随着pH值的增高,析氢反应加剧,Sn离子水解,导致镀层质量下降。运用分步法电镀制备的Au/Sn/Au三层结构薄膜均匀,回流得到了具有典型共晶组织的Au-Sn凸点。

Microstructure of Au-Sn eutectic bumps prepared by sequential electroplating

The effects of molar concentration ratio of metal ion to complexing agent,pH value and electroplating temperature on the morphology and the plating rate of gold and tin films were investigated.The Au/Sn/Au triple-layer films were prepared by sequential electroplating,and the Au-Sn eutectic bumps were obtained by reflowing the triple-layer films.The results show that the grain size of gold films becomes fine with increasing molar ratio of gold ion to sodium sulfite,and the fastest plating rate is obtained when the molar concentration ratio is 1:6.The gold films are porous at a low temperature,but become dense and smooth with increasing temperature.The tin films become coarsening with more voids with increasing molar ratio.When the pH value is 8.0,the tin films are even and compact.When the pH value is further increased,the quality of tin films gets worse due to the hydrogen revolution reaction and the hydrolysis of tin ions.The Au/Sn/Au triple-layer films prepared by sequential electroplating are uniform,and the Au-Sn bumps with typical eutectic structure are obtained by reflowing the triple-layer film.