顯微組織演化
(1. 上海大學(xué) 材料科學(xué)與工程學(xué)院，上海 200072;
2. 上海大學(xué) 新型顯示與應(yīng)用集成教育部重點實驗室中瑞聯(lián)合微系統(tǒng)集成技術(shù)中心， 上海 200072;
3. 美國偉創(chuàng)立公司 先進組裝和環(huán)境技術(shù)部， San Jose, CA, USA)
摘 要: 研究Sn-Zn基焊料經(jīng)高溫和高濕環(huán)境時效后的顯微組織演化。 在涂覆Au/Ni合金的PCB鍍銅焊盤上焊接3種Sn-Zn基焊料的試樣(Sn-9Zn合金、 Sn-8Zn-3Bi合金以及 Sn-7Zn-Al(30×10-6)合金)， 然后在120 ℃, 100%相對濕度、 2.03×105 Pa下分別時效96 h和192 h。 結(jié)果表明， Zn原子向表面和界面擴散， 形成富Zn相并長大。 粗大的Zn相易于導(dǎo)致O元素的富集， 使與β-Sn界面弱化， 從而降低在位移控制加載模式下的低周疲勞壽命。
關(guān)鍵字: Sn-Zn 基焊料； 時效； 濕度； 顯微組織； 低周疲勞
（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
