The beneficial effect of Zn additions on the microstructure of SnCu and SnCuNi solder joints to Cu substrates

Wayne Ng, Guang Zeng, Takatoshi Nishimura, Keith Sweatman, Stuart D. McDonald, Kazuhiro Nogita

Research output: Chapter in Book/Report/Conference proceedingConference contribution

2 Citations (Scopus)

Abstract

The commercial success as Pb-free solders of alloys based on a trace addition of Ni to Sn-0.7Cu and the academic recognition of the metallurgical effects that deliver the excellent performance in soldering processes and in service, means that Sn-Cu-Ni is now well established as one of the main alloy systems on which the electronics industry depends for the assembly of reliable circuitry. One important effect of the Ni addition is the stabilization of the hexagonal form of the Cu6Sn5 phase that forms at the interface between the solder and the Cu substrate. However, with the limited amount of Ni available in a solder joint, growth of the intermetallic layer by reaction with a copper substrate can result in the Ni level in the Cu6Sn5 falling below that required for stabilization. Increasing the Ni in the solder alloy beyond the level required for optimization of properties such as fluidity that are important in soldering processes can result in the appearance of undesirable high melting point Sn-Ni phases, It would therefore be useful if a second stabilizing element could be introduced to the system to support the effect of the Ni. Ni works as a stabilizer by partially substituting for Cu in the Cu6Sn5 so potential additives were considered on the basis of reports of their partially replacing either Cu or Ni in that crystal structure. Zn was selected for this study because it can partially substitute for Sn in the Cu6Sn5 crystal, potentially complementing the role of Ni. The effect of a Zn addition was studied in the basic Sn-0.7Cu and when there was also an addition of Ni. By itself a Zn addition did not promote a eutectic microstructure in the way that a Ni addition does so powerfully but alone or with Ni it substantially reduced undercooling and in the alloy with both Ni and Zn there was an overall refinement in the near completely eutectic microstructure. In combination with the Ni the Zn significantly refined the grain size of the Cu6Sn5 that formed at the solder/Cu interface. By itself the Zn did not suppress the formation of Cu3Sn at the interface between the Cu and the Cu6Sn5 in the way that Ni does but it does not interfere with that beneficial effect of the Ni. Diffraction studies with high energy synchrotron-generated X-rays confirm that as well as stabilizing the hexagonal form of the Cu6Sn5, Zn reduces the anisotropy of this phase and increases the randomness of the crystal orientation in the intermetallic layer. These effects should result in a stronger intermetallic layer that is less likely to degrade during thermal cycling. The combination of all of these effects mean that an addition of Zn to the widely used Sn-Cu-Ni lead free solders should result in an overall increase in reliability of the solder joint, particularly in harsh environments.

Original languageEnglish
Title of host publicationICEP-IAAC 2015 - 2015 International Conference on Electronic Packaging and iMAPS All Asia Conference
PublisherInstitute of Electrical and Electronics Engineers Inc.
Pages809-813
Number of pages5
ISBN (Electronic)9784904090138
DOIs
Publication statusPublished - May 20 2015
Event2015 International Conference on Electronic Packaging and iMAPS All Asia Conference, ICEP-IAAC 2015 - Kyoto, Japan
Duration: Apr 14 2015Apr 17 2015

Publication series

NameICEP-IAAC 2015 - 2015 International Conference on Electronic Packaging and iMAPS All Asia Conference

Other

Other2015 International Conference on Electronic Packaging and iMAPS All Asia Conference, ICEP-IAAC 2015
CountryJapan
CityKyoto
Period4/14/154/17/15

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All Science Journal Classification (ASJC) codes

  • Electrical and Electronic Engineering

Cite this

Ng, W., Zeng, G., Nishimura, T., Sweatman, K., McDonald, S. D., & Nogita, K. (2015). The beneficial effect of Zn additions on the microstructure of SnCu and SnCuNi solder joints to Cu substrates. In ICEP-IAAC 2015 - 2015 International Conference on Electronic Packaging and iMAPS All Asia Conference (pp. 809-813). [7111122] (ICEP-IAAC 2015 - 2015 International Conference on Electronic Packaging and iMAPS All Asia Conference). Institute of Electrical and Electronics Engineers Inc.. https://doi.org/10.1109/ICEP-IAAC.2015.7111122