Title: The influence of nano-particles on microstructural development at the interface of Sn3.5Ag-solder and Cu-substrate

Authors: D.C. Lin, T.S. Srivatsan, G-X. Wang, R. Kovacevic

Addresses: Department of Mechanical Engineering, Research Center for Advanced Manufacturing, Southern Methodist University, 3101 Dyer Street, Dallas TX 75205, USA. ' Division of Materials Science and Engineering, Department of Mechanical Engineering, The University of Akron, 302 E. Buchtel Mall, Akron OH 44325, USA. ' Division of Materials Science and Engineering, Department of Mechanical Engineering, The University of Akron, 302 E. Buchtel Mall, Akron OH 44325, USA. ' Department of Mechanical Engineering, Research Center for Advanced Manufacturing, Southern Methodist University, 3101 Dyer Street, Dallas TX 75205, USA

Abstract: Preliminary experimental results have shown that an unexpected large needle-like phase Ag3Sn grows from the solder/substrate interface and large polygon-like Sn-Cu intermetallic compounds are present in the region, which is close to the interface when using lead-free binary Sn3.5Ag solder alloy. This paper summarises the efforts made to prevent the formation of these deleterious phases. An addition of 0.25 wt% of either copper nano-particles or nickel nano-particles was found to effectively avoid the formation of large Ag3Sn phase and to modify the solder matrix through a random dispersion of the in-situ intermetallic compounds Cu6Sn5 or Sn4Ni3. The mechanism involved in influencing the interfacial structure is quite different for copper and nickel nano-particles. The addition of copper nano-particles stimulates the formation of the Sn-Cu compound Cu6Sn5 at the solder/substrate interface, while the nickel nano-particles promotes the formation of Sn-Cu-Ni-Ag compound to replace the regular scallop-like Cu6Sn5 having a round morphology.

Keywords: lead free solders; Sn3.5Ag solder; interfacial structures; nanoparticles; microstructure; reinforcement; nickel; copper; nanomanufacturing; intermetallic compounds; tin-silver solder; solidification kinetics; soldering.

DOI: 10.1504/IJNM.2007.013683

International Journal of Nanomanufacturing, 2007 Vol.1 No.3, pp.357 - 369

Published online: 11 May 2007 *

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