氮气气氛下氧含量对Sn-Zn/Cu焊接接头组织的影响及其产业应用

Effects of oxygen content in nitrogen shielding gas on microstructure of Sn-Zn/Cu welded joint and its industrial application

Sn-Zn系无铅焊料具有熔点低、电导率高、力学性能好等优点,但焊锡易氧化、润湿性差,波峰焊容易产生拉尖、桥连、填充不足等焊接缺陷,制约了Sn-Zn系无铅焊料的产业化应用。对波峰焊机加装氮气保护装置,通过控制氮气流量调控焊接过程中焊锡表面的氧含量,探究氧含量对接头的焊接效果与微观组织的影响,并进行Sn-Zn/Cu焊接接头高温老化机理研究。结果表明,氧含量与金属间化合物(IMC)γ-Cu5Zn8的生长速度呈正相关关系;在氧含量小于2%条件下,研制的SnZn系无铅焊料在波峰焊过程中基本不存在焊接缺陷;高温老化过程中,当靠近IMC处焊料中Zn含量为1%左右时,接头开始出现柯肯达尔孔洞。在氧含量1. 2%、焊接温度225℃、传输速度1 600 mm/min的工艺条件下进行了生产线试验,并通过了行业内可靠性验证。

Sn-Zn lead-free solder has a low melting point,high electrical conductivity,and good mechanical properties,but its bad oxidation resistance and wettability restrict the industrial application of Sn-Zn lead-free solder,which may cause wave soldering defects such as sharpening,bridging,and insufficient filling. A nitrogen protection device on the wave soldering machine was installed and the oxygen content of the solder surface during the welding process was controled by controlling the nitrogen flow. Furthermore,the effect of oxygen content on the welding effect and microstructure of the joint was investigated,and the high-temperature aging mechanism study on Sn-Zn/Cu welded joints was explored. The results show that there is a positive correlation between the oxygen content and the growth rate of the intermetallic compound( IMC) γ-Cu5Zn8. Under the condition that the oxygen content is less than 2%,the developed Sn-Zn lead-free solder won’t cause soldering defects during the wave soldering process,basically. During the high-temperature aging process,when the content of Zn in the solder near the intermetallic compound is about 1%,we find that Kirkendall Holes begin to appear in the joints. Production line test was conducted under the process conditions of 1. 2% oxygen content,welding temperature of 225 ℃ and transmission speed of 1 600 mm/min,and passed the reliability verification in the industry.