Effect of Lanthanum Addition on the Microstructure Evolution and Adhesive Strength of Sn-Ag-Sb Lead-Free Solder Joints

• Main Authors: Yu-ChingHuang, 黃于菁
• Other Authors: Hwa-Teng Lee
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/67872517049187510136

碩士 === 國立成功大學 === 機械工程學系碩博士班 === 98 === The effects of adding 0 ~ 0.5 wt.% La into Sn-3Ag-2Sb-xLa/Cu lead-free solder joints on microstructure, microhardness, adhesive strength, as well as the interfacial IMC (Intermetallic Compound) layers were studied in this research. The influences of different La addition on the adhesive strength of solder joint and thermal resistance were evaluated by performing high temperature storage tests with hot-dipped specimen. Experimental results showed that microstructure of solder joints were mainly composed of ε-Ag3Sn and coarse β-Sn. However, a new phase, LaSb IMC, formed when the La contents is more than 0.1 wt.%. And LaSb amount is increased with the increasing La content. After thermal aging, the size of LaSb IMCs won’t be changed and remained the same. The addition of trace La element decreased the size of Ag3Sn and Cu6Sn5 particles and β-Sn grains as well. The microstructure become more uniform. With the increasing La content, the thickness of IMC layer of SASxLa/Cu were decreased. It revealed that La addition can prevent IMC layer from growing. The adhesive strength tests show that the SAS0.05La/Cu solder joint has the highest adhesive strength, and decreased with the increasing La content. The strength of all solder joints decreased dramatically after thermal storage at 150 oC for 400 hours. Particularly for 3.5Ag/Cu solder joint, the adhesive strength decreased from 68.35 MPa to 56.27 MPa; however, the strength of SAS0.05La/Cu solder joint were 70.32 Mpa. And the fracture modes were transited from solder mode to mix mode due to the IMC layer growth. Comparing all the results of the study, the SAS0.05La/Cu solder joint has the better mechanical properties.