Effects of Ce and La Additions on the Microstructure and Mechanical Properties of Sn-9Zn Solder Joints
Resource
Journal of Electronic Materials, 39(2), 200-208
Journal
Journal of Electronic Materials
Pages
200-208
Date Issued
2010
Date
2010
Author(s)
Lin, Hsiu-Jen
Abstract
The effects of rare-earth elements on the microstructure and mechanical properties of Sn-9Zn alloys and solder joints in ball grid array packages with Ni/Au(ENIG) surface finishes have been investigated. Metallographic observations showed that (Ce 0.8Zn 0.2)Sn 3 and (La 0.9Zn 0.1)Sn 3 intermetallic compounds appeared in the solder matrix of Sn-9Zn-0.5Ce and Sn-9Zn-0.5La alloys, respectively. Both fiber- and hillock-shaped tin whiskers were inhibited in the Sn-9Zn-0.5Ce solder, while tin fibers were still observed on the surface of oxidized (La 0.9Zn 0.1)Sn 3 intermetallics in Sn-9Zn-0.5La after air exposure at room temperature. Mechanical testing indicated that the tensile strength of Sn-9Zn alloys doped with Ce and La increased significantly, and the elongation decreased, in comparison with the undoped Sn-9Zn. The bonding strengths of the as-reflowed Sn-9Zn-0.5Ce and Sn-9Zn-0.5La solder joints were also improved. However, aging treatment at 100°C and 150°C caused degradation of ball shear strength in all specimens. During the reflowing and aging processes, AuZn 8 intermetallic phases appeared at the interfaces of all solder joints. In addition, Zn-rich phases were observed to migrate from the solder matrix to the solder/pad interfaces of the aged specimens. © 2009 TMS.
Type
journal article
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