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Effect of Gold Content on the Microstructural Evolution of SAC305 Solder Joints Under Isothermal Aging

Journal of Electronic Materials volume 41, pages 224–231 (2012)Cite this article

Abstract

Au over Ni on Cu is a widely used printed circuit board (PCB) surface finish, under bump metallization (UBM), and component lead metallization. It is generally accepted that less than 3 wt.% Au in Sn-Pb solder joints inhibits formation of detrimental intermetallic compounds (IMC). However, the critical limit for Au content in Pb-free solder joints is not well established. Three surface-mount package platforms, one with a matte Sn surface finish and the others with Ni/Au finish, were soldered to Ni/Au-finished PCB using Sn-3.0Ag-0.5Cu (SAC305) solder, in a realistic manufacturing setting. The assembled boards were divided into three groups: one without any thermal treatment, one subjected to isothermal aging at 125°C for 30 days, and the third group aged at 125°C for 56 days. Representative solder joints were cross-sectioned and analyzed using scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) to investigate the evolution of the solder joint morphology as a function of Au content and isothermal aging. It was found that, if Cu is available to dissolve in the solder joint, the migration of AuSn4 from the bulk to the interface as a result of thermal aging is mitigated.

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Authors and Affiliations

  1. Agilent Technologies, Santa Rosa, CA, 95403, USA

    Mike Powers & Julie Silk

  2. California Polytechnic State University, San Luis Obispo, CA, 93407, USA

    Jianbiao Pan & Patrick Hyland

Authors
  1. Mike Powers
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  2. Jianbiao Pan
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  3. Julie Silk
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  4. Patrick Hyland
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Correspondence to Mike Powers.

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Powers, M., Pan, J., Silk, J. et al. Effect of Gold Content on the Microstructural Evolution of SAC305 Solder Joints Under Isothermal Aging. J. Electron. Mater. 41, 224–231 (2012). https://doi.org/10.1007/s11664-011-1744-4

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  • DOI: https://doi.org/10.1007/s11664-011-1744-4

Keywords

  • Pb-free solder
  • isothermal aging
  • Ni/Au surface finish
  • Au content
  • Sn-Ag-Cu
  • intermetallic compound