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Title: Rapid Solidification of Sn-Cu-Al Alloys for High-Reliability, Lead-Free Solder: Part II. Intermetallic Coarsening Behavior of Rapidly Solidified Solders After Multiple Reflows

Controlling the size, dispersion, and stability of intermetallic compounds in lead-free solder alloys is vital to creating reliable solder joints regardless of how many times the solder joints are melted and resolidified (reflowed) during circuit board assembly. In this article, the coarsening behavior of Cu x Al y and Cu 6Sn 5 in two Sn-Cu-Al alloys, a Sn-2.59Cu-0.43Al at. pct alloy produced via drip atomization and a Sn-5.39Cu-1.69Al at. pct alloy produced via melt spinning at a 5-m/s wheel speed, was characterized after multiple (1-5) reflow cycles via differential scanning calorimetry between the temperatures of 293 K and 523 K (20 °C and 250 °C). Little-to-no coarsening of the Cu x Al y particles was observed for either composition; however, clustering of Cu x Al y particles was observed. For Cu 6Sn 5 particle growth, a bimodal size distribution was observed for the drip atomized alloy, with large, faceted growth of Cu 6Sn 5 observed, while in the melt spun alloy, Cu 6Sn 5 particles displayed no significant increase in the average particle size, with irregularly shaped, nonfaceted Cu 6Sn 5 particles observed after reflow, which is consistent with shapes observed in the as-solidified alloys. The link between original alloymore » composition, reflow undercooling, and subsequent intermetallic coarsening behavior was discussed by using calculated solidification paths. As a result, the reflowed microstructures suggested that the heteroepitaxial relationship previously observed between the Cu x Al y and the Cu 6Sn 5 was maintained for both alloys.« less
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  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: 3739
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; calorimetry; metallography; scanning electron microscopy; SEM
OSTI Identifier: