显微组织演化
(1. 上海大学 材料科学与工程学院，上海 200072;
2. 上海大学 新型显示与应用集成教育部重点实验室中瑞联合微系统集成技术中心， 上海 200072;
3. 美国伟创立公司 先进组装和环境技术部， San Jose, CA, USA)
摘 要: 研究Sn-Zn基焊料经高温和高湿环境时效后的显微组织演化。 在涂覆Au/Ni合金的PCB镀铜焊盘上焊接3种Sn-Zn基焊料的试样(Sn-9Zn合金、 Sn-8Zn-3Bi合金以及 Sn-7Zn-Al(30×10-6)合金)， 然后在120 ℃, 100%相对湿度、 2.03×105 Pa下分别时效96 h和192 h。 结果表明， Zn原子向表面和界面扩散， 形成富Zn相并长大。 粗大的Zn相易于导致O元素的富集， 使与β-Sn界面弱化， 从而降低在位移控制加载模式下的低周疲劳寿命。
关键字: Sn-Zn 基焊料； 时效； 湿度； 显微组织； 低周疲劳
（1. School of Materials Science and Engineering, Shanghai University,
Shanghai 200072, China;
2. Sino-Swedish Microsystem Integration Technology (SMIT) Centre,
Shanghai University, Shanghai 200072, China;
3. Advanced Assembly and Environmental Technologies,
Flextronics Corporate Technology Group, San Jose, California, USA）
Abstract: The Sn-Zn based lead free solder appears to be an attractive alternative with a melting temperature relatively close to eutectic Sn-Pb. The addition of bismuth in Sn-Zn alloy improves its wettability and aluminum is beneficial to improve the oxidation resistance. The degradation of Sn-Zn based solder joints after exposed in the temperature and humid atmosphere with high pressure was studied. Three kinds of Sn-Zn system solders (Sn-9Zn, Sn-8Zn-3Bi and Sn-7Zn-Al (30×10-6)) were soldered on copper pad with a layer of Au/Ni and the specimens were stored in a pressure cooker for 96 or 192 h. The temperature and the relative humidity in the cooker were 120 ℃ and 100% respectively. The mechanical fatigue test was carried in a displacement-controlled mode to measure the low cycle fatigue of the joints. The results show that Zn diffuses to the surface and interface while coarsening at the same time, and the coarser Zn has weak interface with β-Sn matrix and oxides form. High temperature and high humidity exposure decreases the mean life of Sn-Zn solder joints when they are subjected to 120 ℃ and 100% relative humidity with 2.03×105 Pa pressure for 192 h.
Key words: Sn-Zn based solder; aging; humidity; microstructure; low cycle fatigue
