研究了240 ℃,温度梯度为1045 ℃/cm的热迁移条件下Cu含量对Ni/Sn-xCu/Ni (x=0.3、0.7、1.5,质量分数,%)微焊点钎焊界面反应的影响。结果表明,在热迁移过程中微焊点发生了界面金属间化合物(IMC)的非对称生长和转变以及Ni基体的非对称溶解。在Ni/Sn-0.3Cu/Ni微焊点中,虽然界面IMC类型始终为初始的(Ni, Cu)3Sn4,但出现冷端界面IMC厚度明显大于热端的非对称生长现象。在Ni/Sn-0.7Cu/Ni和Ni/Sn-1.5Cu/Ni微焊点中,界面IMC类型逐渐由初始的(Cu, Ni)6Sn5转变为(Ni, Cu)3Sn4,且出现冷端滞后于热端的非对称转变现象;Ni/Sn-1.5Cu/Ni微焊点冷、热端发生IMC转变的时间均滞后于Ni/Sn-0.7Cu/Ni微焊点。通过分析微焊点冷、热端界面IMC生长所需Cu和Ni原子通量,确定Cu和Ni的热迁移方向均由热端指向冷端。微焊点中的Cu含量显著影响主热迁移元素的种类,进而影响冷、热端界面IMC的生长和转变规律。此外,热迁移促进了热端Ni原子向钎料中的扩散,加速了热端Ni基体的溶解,溶解到钎料中的Ni原子大部分迁移到冷端并参与界面反应。相反,热迁移显著抑制了冷端Ni原子的扩散,因此冷端Ni基体几乎不溶解。
The effect of Cu content on the evolution of intermetallic compounds (IMCs) in Ni/Sn-xCu/Ni (x= 0.3, 0.7, 1.5, mass fraction, %) micro solder joints during soldering at 240 ℃ under a temperature gradient of 1045 ℃/cm was investigated. Asymmetrical growth and transformation of interfacial IMCs and asymmetrical dissolution of Ni substrate were clearly observed. In Ni/Sn-0.3Cu/Ni micro solder joints, though the interfacial IMC remained as the initial (Ni, Cu)3Sn4, asymmetrical IMC growth between cold and hot ends occurred, i.e., the (Ni, Cu)3Sn4 IMC at the cold end was obviously thicker than that at the hot end. In Ni/Sn-0.7Cu/Ni and Ni/Sn-1.5Cu/Ni micro solder joints, the interfacial IMC gradually transformed from the initial (Cu, Ni)6Sn5 into (Ni,Cu)3Sn4. Meanwhile, the transformation at the cold end lagged behind the hot end, namely asymmetrical transformation phenomenon occurred. Moreover, the transformations at the cold and hot ends in the Ni/Sn-1.5Cu/Ni micro solder joints both lagged behind those in the Ni/Sn-0.7Cu/Ni micro solder joints. Based on the analysis of the Cu and Ni atomic fluxes for the IMC growth at both cold and hot ends, the thermomigration (TM) direction was confirmed to be from the hot end towards the cold end. The Cu concentration in the micro solder joints had a significant effect on the main TM element, and thus affected the growth and transformation behavior of the interfacial IMCs at the two ends. In addition, TM promoted the diffusion of Ni atoms into solder at the hot end, which accelerated the dissolution of the hot end Ni substrate. Most of the dissolved Ni atoms migrated to the cold end and participated in interfacial reaction locally. On the contrary, TM inhibited the diffusion of Ni atoms at the hot end, resulting in no obvious dissolution of the cold end Ni substrate.
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