纯锡镀层锡须生长机理及聚氯代对二甲苯膜抑制效果研究

Study on mechanism of whisker growth of pure tin coating and the suppression effect of Parylene C film

以无铅器件及无铅引线框架为研究对象,采用扫描电镜、能谱分析了纯锡镀层锡须生长机理。采用化学气相沉积(CVD)法在样品表面镀聚氯代对二甲苯(PC)膜,研究了PC膜对锡须生长的抑制效果。结果表明:Cu/Sn界面处金属间化合物(IMC)易于向Sn晶界处生长,使得原位体积增加44.8%,因此界面处会产生较大压应力。此压应力会随着镀层/基体界面IMC层的不规则形成而增大。在压应力的作用下,Sn被挤出,从而形成锡须。PC膜对锡须的生长具有明显的抑制作用,且随着PC膜厚度的增大,锡须生长变慢,孕育期更长。5μm厚的PC膜能有效抑制锡须生长。

The mechanism of tin whisker growth of pure tin coating on lead-free devices and leadframes was analyzed by scanning electron microscopy and energy-dispersive spectroscopy. Parylene C （PC） film was deposited on pure tin coating surface by chemical vapor deposition （CVD） and its suppression effect on tin whisker growth was studied. The results showed that the intermetallic compound （IMC） at Cu/Sn interface usually grows toward tin grain boundaries, leading to an in-situ increase of volume by 44.8% and the generation of compressive stress, which is increased with the growth of irregular IMC layer at the substrate/coating interface. The tin coating is extruded under the action of compressive stress, resulting in the formation of tin whisker. The PC film can suppress the growth of tin whisker obviously. The thicker the PC film is, the slower the tin whisker and the longer the incubation time are. A 5 μm-thick PC film effectively suppresses the growth of tin whisker.