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以Sn-0.3Ag-0.7Cu低银无铅钎料为研究对象,添加不同量的Bi(1.0%～4.5%)元素,和Cu盘进行钎焊,取部分试样进行高温时效处理。观察分析了Bi对钎料微观组织结构的影响,以及Bi对焊接接头界面金属间化合物(IMC)显微形貌演变、生长动力学和接头剪切强度的影响。研究结果表明;Bi元素的加入使钎料基体内晶粒尺寸变得细化而均匀,且随着Bi含量的增加可以显著提高钎料钎焊接头的剪切强度,断口经过扫描电镜观察发现剪切断面均沿着剪切方向有明显的塑性变形,这表明焊点中发生的是塑性断裂;高温时效试验表明,钎料基体中Bi的存在降低了界面IMC的生长速率,且随着Bi含量的增加,抑制IMC生长的作用越大。但是过量的Bi会使组织粗化,且对IMC生长的抑制作用反而会变差。IMC层厚度随着时效时间的延长明显增加,断裂机制很快由钎料基体的韧性断裂逐渐变为界面IMC的脆性断裂,使焊接接头的剪切强度明显下降。
The Sn-0.3Ag-0.7Cu low-silver lead-free solder was used as the research object. Different amounts of Bi (1.0% -4.5%) were added into the brazing filler metal and brazed with Cu plate. Some samples were taken for high temperature aging treatment. The effects of Bi on the microstructure of the solder and the effect of Bi on the morphology, growth kinetics and shear strength of the interfacial intermetallic compound (IMC) were observed and analyzed. The results show that the addition of Bi can refine the grain size of the solder matrix and increase the shear strength of brazing filler metal significantly with the increase of Bi content. The results show that plastic deformation occurs along the shear direction, which indicates that plastic fracture occurs in the solder joint. The high temperature aging test shows that the presence of Bi in the solder matrix decreases the growth rate of IMC at the interface, and with the Bi content The greater the effect of inhibiting the growth of IMC. Excessive Bi, however, roughens the tissue and inhibits IMC growth on the contrary. The thickness of IMC layer obviously increases with the extension of aging time. The fracture mechanism quickly changes from ductile fracture of the solder matrix to brittle fracture of IMC, which decreases the shear strength of the welded joints obviously.