Nucleation promotion of Sn-Ag-Cu lead-free solder alloys via micro alloying

Mao, Jie
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Lewis, Daniel J.
Duquette, D. J.
Watson, E. Bruce
Wright, Roger N.
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Materials science and engineering
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This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
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Sn-Ag-Cu (SAC) alloy system is widely accepted as a viable Pb-free alternative to Sn-Pb alloys for microelectronics packaging applications. Compared with its Pb-containing predecessor SAC alloys tend to have coarse grain structure, which is believed to be caused by high undercooling prior to nucleation. This work explores the possibility of modifying the nucleation process and reducing the undercooling of SAC alloys via introducing minor alloying elements. The mechanisms through which effective alloying elements influenced the nucleation process of SAC alloys are investigated with microstructural and chemical analyses. Minor alloying elements (Mn and Zn) are found promoting beta-Sn nucleation and reducing the undercooling of SAC. Manganese promotes beta-Sn primary phase nucleation through the formation of MnSn2 intermetallic compound. Experimental results in this work support the claim by previous researchers that zinc promotes beta-Sn primary phase nucleation through the formation of zinc oxide. In addition to nucleation, this work also assesses the microstructural impact of minor elements on Sn-Ag-Cu based alloys. Methods have been developed to quantify and compare microstructural impacts of minor elements and efficiently study their partitioning behaviors. LA-ICPMS was introduced to SAC alloy application to efficiently study partitioning behaviors of minor elements.
May 2014
School of Engineering
Dept. of Materials Science and Engineering
Rensselaer Polytechnic Institute, Troy, NY
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