62Sn-36Pb-2Ag焊点组织及热疲劳裂纹的萌生与扩展

The microstructure and thermal fatigue behaviour of 62Sn--36Ph--2Ag solder joints

研究了表面封装电路中 ６２Ｓｎ－３６Ｐｈ－２Ａｇ焊点的微观组成及－５５～１２５℃热疲劳过程中裂纹的萌生与扩展情况，初步探讨了微观组织变化与焊点热疲劳失效的关系。结果表明：焊点组成主要为先共晶β－Ｓｎ， α－Ｐｂ＋β－Ｓｎ共晶，ＡｕＳｎ４及Ａｇ３Ｓｎ金属间化合物。热疲劳过程中，焊点显微组织发生不均匀粗化，疲劳裂纹萌生于不均匀粗化区的 ＡｕＳｎ４金属间化合物与基体组织的界面或 α－Ｐｂ与 β－Ｓｎ的相界，并沿富Ｓｎ的β相晶界扩展。

Based on the results of tests, the characteristics of crack initiation and propagation in 62Sn--36Ph--2Ag surface mount solder joints during ~ 55-125 C thermal fatigue as well as ths microstructure have been discussed; meanwhile, the relationship between the microstructural evolution and thermal fatigue behaviour has been explained tentatively. It shows that: the microstrueture of solder joints is mainly B--Sn, a--Ph and B--Sn eutectic, AuSn4 and Ag3Sn intermetallic compound; during thermal fatigue, the microstructure will coarsen inhomogeneously, then fatigue crack initiates at the interface of AuSn4/B--Sn or a--Pb/B--Sn in inhomogeneous zone, and propagates along B--Sn grain boundary or through B--Sn phase.