稀土Pr对低银Sn-0.3Ag-0.7Cu-0.5Ga钎料蠕变行为影响的研究

为进一步促进电子封装用低银无铅钎料的发展,本文采用纳米压痕法研究了新型含Pr低银Sn-0.3Ag-0.7Cu-0.5Ga (SAC-Ga)钎料显微组织与蠕变性能之间的关系。结果表明,SAC-Ga、SAC-Ga-0.06Pr、SAC-Ga-0.5Pr三种钎料的蠕变位移分别为1717 nm、1144 nm、1472 nm；稀土Pr可通过细化Cu₆Sn₅金属间化合物并促使其均匀分布从而明显提高SAC-Ga钎料的蠕变强度；与SAC-Ga-0.06Pr钎料相比,SAC-Ga-0.5Pr由于过量稀土Pr的表面氧化而导致其蠕变强度有所下降。此外,本文采用Dorn模型研究了含Pr的SAC-Ga钎料的室温蠕变行为并计算了对应的钎料蠕变应力指数n；阐明了Pr对SAC-Ga钎料蠕变强度的强化机理,即当位错遇到细小且均匀分布的Cu₆Sn₅ 金属间化合物时,位错移动只能采用绕过机制,从而提高了含Pr低银钎料的抗蠕变性能。

Study on creep behavior of Sn-0.3Ag-0.7Cu-0.5Ga low-Ag solder alloys bearing Pr

For development of low-Ag lead free solder alloys for microelectronic packaging, the correlation of creep properties with microstructure of novel Sn-0.3Ag-0.7Cu-0.5Ga (SAC-Ga) solder alloys bearing Pr has been investigated using nanoindentation. The results show that the creep deformation of SAC-Ga, SAC-Ga-0.06Pr, SAC-Ga-0.5Pr is 1717 nm, 1144 nm,1472 nm, respectively, which indicates that Pr addition could significantly enhance the creep resistance of SAC-Ga solders due to the refinement and more uniform distribution of Cu₆Sn₅ intermetallic compounds (IMCs). However, compared with the SAC-Ga-0.06Pr solder alloy, the SAC-Ga-0.5Pr alloy shows lower creep resistance which is mainly attributable to the surface oxidation of excess rare earth Pr. In addition, Dorn model has been used to describe the creep behavior and to obtain stress exponents of the SAC-Ga solder alloys bearing Pr. It is proposed that strengthening mechanism of creep resistance in SAC-Ga solder alloys bearing Pr is that when encountering refined and well-distributed Cu₆Sn₅ IMCs, a dislocation line cannot climb through the IMCs but bypass the IMCs, leading to a decrease in the creep deformation of the solder alloys bearing Pr.