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

Particles of Cu x Al y in Sn-Cu-Al solders have previously been shown to nucleate the Cu 6Sn 5 phase during solidification. In this study, the number and size of Cu 6Sn 5 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 Cu 6Sn 5 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 Cu 6Sn 5 phases. Transitions in the Cu 6Sn 5 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 °C/s were found to be optimal for realizing particle size refinement and maintaining the Cu x Al y /Cu 6Sn 5 nucleant relationship. In addition,more » little evidence of the formation or decomposition of the ternary-β phase in the solidified alloys was noted. As a result, solidification pathways omitting the formation of the ternary-β phase agreed well with observed room temperature microstructures.« less
 [1] ;  [2] ;  [2] ;  [1]
  1. Purdue Univ., West Lafayette, IN (United States)
  2. Ames Lab. and Iowa State Univ., Ames, IA (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1073-5623; PII: 3738; TRN: US1801048
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science
Additional Journal Information:
Journal Volume: 47; Journal Issue: 12; Journal ID: ISSN 1073-5623
ASM International
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
Country of Publication:
United States
36 MATERIALS SCIENCE; intermetallics; rapid-solidification; quenching; microstructure; metallography; scanning electron microscopy; SEM
OSTI Identifier: