Sn-30Bi-0.5Cu低温无铅钎料的微观组织及其力学性能

Microstructures and mechanical properties of Sn-30Bi-0.5Cu low-temperature lead-free solder

通过在Sn-Bi钎料中添加Cu元素制备新型Sn-30Bi-0.5Cu低温无铅钎料,对无铅钎料的力学性能及微观组织进行分析。结果表明:Cu元素的加入抑制Bi元素在钎料/铜界面处的偏析,避免形成粗大的富Bi带,并能够在钎料基体中原位生成Cu-Sn金属间化合物(Intermetallic compounds,IMC);当Cu含量约为0.5%(质量分数)时,钎料的抗拉强度和伸长率等力学性能指标最佳,并能够提高其抗振动可靠性。这主要是由于在钎料基体中原位形成的棒状或杆状IMC能有效地将脆性薄弱面钉扎和在β-Sn软相基体中形成钉轧强化,改善钎料的微观组织形态,从而提高钎焊强度和焊点的抗振动冲击可靠性,使其性能强于Sn-Bi共晶的性能而接近于Sn-Bi-Ag钎料的,Sn-30Bi-0.5Cu钎料在拉伸过程中断口存在韧性和脆性两种混合型断口。

A new type of low-temperature solder, Sn-30Bi-0.5Cu was fabricated by adding Cu elements into the tin-bismuth series solder. The microstructures and mechanical properties of the solder were studied. The results show that the addition of Cu elements can restrain the segregation of bismuth in the interface between solder and Cu pad, prevent the bismuth from forming into bulky crystal as strips, and in-situ form Cu-Sn intermetallic compounds（IMCs） in tin-bismuth solder. When the mass fraction of Cu is about 0.5%, both of the tensile strength and elongation reach to the best values, and the vibration reliability increases. The reason is that the addition of Cu element can improve the microstructures of the Sn-Bi-Cu solder by forming appropriate rod-like shape fine IMC crack pinning and strengthening β-Sn soft matrix, thus strengthening its soldering and vibration mechanical properties which are close to those of Sn-Bi-Ag solder and far more than those of the Sn-Bi eutectic solders. Two types of fracture occur. During the tension tests the fracture surface type of the Sn-30Bi-0.5Cu solder is a mixed fracture surface of plastic and brittle.