Studies on the Interfacial Reactions, Electromigration and Whisker Growth in rare-earth doped solder joints
Date Issued
2007
Date
2007
Author(s)
Lin, Hsiu-Jen
DOI
zh-TW
Abstract
Alloying with rare earth (RE) elements in Pb-free solders has been reported to have beneficial effects on their physical and mechanical properties. Since rare earth elements have a special characteristic of high chemical activity, they can much more easily react with the oxygen in the air and accelerate tin whisker growth in a rare earth element-containing solder alloy. It is known that such whiskers can cause short circuits in solder joints and lead to the failure of electronic devices in application. Addressing the tin whisker problem, first part of this thesis is the research of whisker growth in rare-earth doped solder joints and tries to find out the methods for the inhibition of whisker growth. Furthermore, second part of this dissertation verify the physical and mechanical performances of Sn-Zn and Sn-Ag-Cu solders added with rare earth elements, such as melting points, microstructure, tensile properties, hardness, interfacial reactions, bonding strength, and the behaviors of electromigration.
The smaller size of the Sn-RE clusters leads to the lower amount of tin atoms released and lower compressive stress accumulated after oxidation, which result in the slower whisker and hillock growth in Sn-6.6RE alloy. The prevention of the lengthening and coarsening of tin sprouts in Sn9Zn0.5Ce and Sn9Zn0.5La solder is also attributed to the small size of its rare-earth containing precipitation clusters. According to the studies of whisker growth in Sn6.6RE and Sn9Zn0.5RE alloy, the problem of whisker growth in Sn3Ag0.5Cu0.5Ce solder can be settled by the addition of Zn. However, the wettability of Sn-Ag-Cu solder might be degraded because of adding an excessive amount of Zn into the alloy; hence the addition of 0.2 wt. % Zn into Sn3Ag0.5Cu0.5Ce solder is appropriate.
Adding 0.2 wt. % Zn into Sn3Ag0.5Cu0.5Ce alloy can not only inhibit the growth of whisker but also improve the mechanical properties and bonding strength of solder joints. The addition of RE into Sn9Zn alloy also can improve the behaviors of Sn-Zn alloy, but adding Ce into Sn9Zn is more comportable than the addition of La into Sn9Zn solder. Besides, addition of RE into SnAgCu and SnZn alloy might deteriorate electromigration-induced failure of solder joints due to higher grain boundary diffusivity of RE-doped solder joints.
Subjects
無鉛銲錫
稀土元素
界面反應
電遷移
錫鬚成長
Pb-free solders
rare earth elements
interfacial reactions
electromigration
whisker growth
Type
thesis
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