|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。通过对波峰焊进行氮气改造,课题组研制的Sn-Zn系无铅焊料在氧含量小于20000ppm条件下,基本解决了波峰焊过程中的上述缺陷。在氧含量分别为12000ppm 、20000ppm条件下,采用扫描电镜进行 Sn-Zn系/Cu焊接接头微观组织及接头高温劣化机理的研究,发现氧含量与金属间化合物的生长速度正相关。最后采用氧含量12000ppm、焊接温度225、传输速度1600mm/min的工艺参数进行了产业化验证及焊点老化试验等可靠性验证。
|关键词: Sn-Zn 系 波峰焊 氮气气氛 金属间化合物 产业化试验
|Effects of oxygen content in nitrogen shielding gas on microstructure of Sn-Zn / Cu welded joint and its Industrial application
SUN Wendong, GONG Shiliang, ZHANG Gong, SHI Qingyu
Department of Mechanical Engineering,Tsinghua University
|Sn-Zn lead-free solder has a low melting point, high electrical conductivity, and good mechanical properties, but it has not been applied in the industrial production, due to its bad oxidation resistance and wettability, which may cause wave soldering defects such as sharpening, bridging, and insufficient filling. This research generally solved the above defects by retrofitting the wave soldering equipment with nitrogen shielding gas. The Sn-Zn solder developed by our research group has good performance when the oxygen content in the nitrogen shielding gas is less than 20000 ppm. The microstructures of Sn-Zn/Cu solder joints were observed by scanning electron microscope (SEM) and the high temperature degradation mechanism of the joints were studied. It shows that the growth speed of intermetallic compounds (IMC) is positive related to the oxygen content. A successful industrialization verification was performed using soldering parameters of 12000ppm oxygen content, 225 welding temperature and 1600mm/min transmission speed, and its aging reliability was verified.
|Key words: Sn-Zn system wave soldering nitrogen shielding gas IMC industrialization verification