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Rapid Solidification of Sn-Cu-Al Alloys for High-Reliability, Lead-Free Solder: Part I. Microstructural Characterization of Rapidly Solidified Solders

TitleRapid Solidification of Sn-Cu-Al Alloys for High-Reliability, Lead-Free Solder: Part I. Microstructural Characterization of Rapidly Solidified Solders
Publication TypeJournal Article
Year of Publication2016
AuthorsReeve, KN, Choquette, SM, Anderson, IE, Handwerker, CA
JournalMetallurgical and Materials Transactions a-Physical Metallurgy and Materials Science
Volume47A
Pagination6507-6525
Date Published12
Type of ArticleArticle
ISBN Number1073-5623
Accession NumberWOS:000387856000086
Keywordsbeta-phase, copper, cu6sn5, diagram, heterogeneous nucleation, Materials Science, Metallurgical Engineering, phase-equilibria, system
Abstract

Particles of Cu (x) Al (y) in Sn-Cu-Al solders have previously been shown to nucleate the Cu6Sn5 phase during solidification. In this study, the number and size of Cu6Sn5 nucleation sites were controlled through the particle size refinement of Cu (x) Al (y) via rapid solidification processing and controlled cooling in a differential scanning calorimeter. Cooling rates spanning eight orders of magnitude were used to refine the average Cu (x) Al (y) and Cu6Sn5 particle sizes down to submicron ranges. The average particle sizes, particle size distributions, and morphologies in the microstructures were analyzed as a function of alloy composition and cooling rate. Deep etching of the samples revealed the three-dimensional microstructures and illuminated the epitaxial and morphological relationships between the Cu (x) Al (y) and Cu6Sn5 phases. Transitions in the Cu6Sn5 particle morphologies from faceted rods to nonfaceted, equiaxed particles were observed as a function of both cooling rate and composition. Initial solidification cooling rates within the range of 10(3) to 10(4) A degrees C/s were found to be optimal for realizing particle size refinement and maintaining the Cu (x) Al (y) /Cu6Sn5 nucleant relationship. In addition, little evidence of the formation or decomposition of the ternary-beta phase in the solidified alloys was noted. Solidification pathways omitting the formation of the ternary-beta phase agreed well with observed room temperature microstructures.

DOI10.1007/s11661-016-3738-6
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Alternate JournalMetall. Mater. Trans. A-Phys. Metall. Mater. Sci.