三元系Sn-Bi-Ag焊料合金相结构,组织与性能研究

Phase Structure, Microstructure and Properties of Ternary Sn-Bi-Ag Solder Alloy

在很多情况下,待焊接器件对温度敏感,需要低温焊接, Sn-Bi二元合金共晶温度为139℃,能够满足低温焊料的要求,但Bi的加入会使材料变脆,加入少量Ag形成金属间化合物Ag_3Sn可改善合金的脆性。以纯度为99.95%的锡、铋及银为原料按一定比例熔融,浇铸成一定形状的试样,利用X射线衍射仪(XRD),金相显微镜(OM),热分析仪,扫描电镜(SEM),万能材料试验机,可焊性测试仪检测样品的物相、组织、熔点、显微形貌、化学组成、抗拉强度和可焊性。研究Bi和Ag对相组成、组织、熔点和可焊性等的影响,分析了SnBiAg三元相图的冷却凝固过程。结果表明:经过XRD检测可知, SnBiAg合金的主晶相为体心立方结构的β-Sn相和菱形层状结构的Bi相。冷却凝固过程中,先析出β-Sn相,随后析出Ag_3Sn相和Bi相。随着Bi相增多, Sn相减少, Ag_3Sn相变化不明显,符合相平衡原理;随着Ag的增加, Sn相、 Bi相基本没有变化,而Ag_3Sn相随Ag含量的增加而增加。Bi含量增加,熔点略有降低, Bi相由条状变成块状,润湿性总体变差; Ag含量增加,可降低Bi的偏析,熔点不变,润湿性变好,最终确定了较佳的合金配方为Sn-38Bi-0.7Ag。

In many cases, due to the soldering device was sensitive to temperature, low temperature welding was necessary. The eutectic temperature of Sn-Bi binary alloy was 139 ℃, and it could meet the requirements of low-temperature solder. Though the addition of Bi would make the material brittle, the intermetallic compound Ag3Sn by adding a small amount of Ag could improve brittleness of the alloy. The specimens with 99.95% purity of tin, bismuth and silver were melted in a certain proportion to form a certain shape. The phases, organization, melting point, microstructure, chemical composition, tensile strength and weldability of the samples were measured by X-ray diffraction(XRD), optical microscope(OM), thermal analyzer, scanning electron microscope(SEM), universal material testing machine and solder ability tester. The effects of Bi and Ag on phase composition, microstructure, melting point and weld ability were studied.The cooling and solidification process of SnBiAg three-phase diagram was analyzed. The results showed that the main crystalline phases of SnBiAg alloy were B-Sn phase with BCC structure and Bi phase with rhombic layered structure according to the XRD test. During the cooling and solidification process, the β-Sn phase was precipitated, and the Ag3Sn and Bi phases were subsequently precipitated. With the increase of Bi phase, Sn phase decreased and Ag3Sn phase was basically unchanged. The result was consistent with the phase equilibrium principle, the Sn phase and Bi phase did not change, and Ag3Sn phase increased with the increase of Ag content. As Bi content increased, the melting point decreased slightly, Bi phase changed from strip to lump, and the overall wettability became worse. As the Ag content increased, the segregation of Bi could be reduced, the melting point remained unchanged and the wettability was improved. Finally, the better alloy formula was Sn-38 Bi-0.7 Ag.