超声促进Ni/Sn固-液溶解行为

钎焊接头的可靠性主要由界面金属间化合物的形貌及接头微观组织决定,超声辅助钎焊过程中母材溶解行为直接影响接头可靠性。为进一步探明超声对Ni-Sn溶解行为的影响,本文采用浸入实验法对比研究了加载超声和无超声辅助下Ni在Sn中的溶解动力学,通过模拟探明了熔池中声压分布规律,观察了Ni-Sn界面微观组织。上述研究表明,超声作用10 s Ni丝的溶解量与不加超声保温5 min的溶解量相当,表明超声能促进Ni在熔融Sn钎料中的溶解。无超声辅助时,随着保温时间的增加,Ni-Sn界面金属间化合物逐渐增厚,阻碍了Ni与Sn 之间的相互扩散；而在超声空化作用下,Ni-Sn界面处于动态非平衡状态,能促进Ni在液态Sn中不断溶解；同时,在声流作用下界面Ni原子快速迁移至Sn中,在随后的冷却过程中析出大量细长棒状的Ni₃Sn₄金属间化合物。

Effect of Ultrasound on Dissolution Acceleration Behavior of Ni/Sn

The reliability of the joint is mainly determined by the morphology of interfacial IMC and microstructure in joint. In the ultrasonic-assisted soldering process, the behavior of the base metal being dissolved by the liquid solder affects the microstructure of the joint. In this paper, the dissolution behavior of Ni in molten Sn solder with and without applied ultrasonic vibration (USV) was investigated through the immersion experiment. In order to reveal the mechanism of accelerated dissolution by USV, the ultrasonic pressure distribution in molten solder were simulated by finite element analysis and the microstructures after dissolution were observed. The results showed the dissolution amount of Ni in Sn after 10 s of USV was equivalent to a holding time of 5 min without USV. Without USV, the interfacial IMC gradually thicken as the holding time increases, which hinders the diffusion of Ni atoms into the Sn solder. With USV, ultrasonic cavitation caused the infinite dissolution of Ni into tin solder. Furthermore, the dissolved Ni atom at the interface was brought rapidly to the molten solder by the ultrasonic streaming, which cause a large number of elongated rod-shaped Ni3Sn4 precipitated during the subsequent cooling process.