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http://dx.doi.org/10.3365/KJMM.2010.48.11.1041

Retardation of Massive Spalling by Palladium Layer Addition to Surface Finish  

Lee, Dae-Hyun (Department of Materials Science and Engineering, Korea University)
Chung, Bo-Mook (Department of Materials Science and Engineering, Korea University)
Huh, Joo-Youl (Department of Materials Science and Engineering, Korea University)
Publication Information
Korean Journal of Metals and Materials / v.48, no.11, 2010 , pp. 1041-1046 More about this Journal
Abstract
The reactions between a Sn-3.0Ag-0.5Cu solder alloy and electroless Ni/electroless Pd/immersion Au (ENEPIG) surface finishes with various Pd layer thicknesses (0, 0.05, 0.1, 0.2, $0.4{\mu}m$) were examined for the effect of the Pd layer on the massive spalling of the $(Cu,Ni)_6Sn_5$ layer during reflow at $235^{\circ}C$. The thin layer deposition of an electroless Pd (EP) between the electroless Ni ($7{\mu}m$) and immersion Au ($0.06{\mu}m$) plating on the Cu substrate significantly retarded the massive spalling of the $(Cu,Ni)_6Sn_5$ layer during reflow. Its retarding effect increased with an increasing EP layer thickness. When the EP layer was thin (${\leq}0.1{\mu}m$), the retardation of the massive spalling was attributed to a reduced growth rate of the $(Cu,Ni)_6Sn_5$ layer and thus to a lowered consumption rate of Cu in the bulk solder during reflow. However, when the EP layer was thick (${\geq}0.2{\mu}m$), the initially dissolved Pd atoms in the molten solder resettled as $(Pd,Ni)Sn_4$ precipitates near the solder/$(Cu,Ni)_6Sn_5$ interface with an increasing reflow time. Since the Pd resettlement requires a continuous Ni supply across the $(Cu,Ni)_6Sn_5$ layer from the Ni(P) substrate, it suppressed the formation of $(Ni,Cu)_3Sn_4$ at the $(Cu,Ni)_6Sn_5/Ni(P)$ interface and retarded the massive spalling of the $(Cu,Ni)_6Sn_5$ layer.
Keywords
electronic matrials; soldering; microstructure; scanning electron microscopy; palladium surface finish;
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Times Cited By KSCI : 1  (Citation Analysis)
Times Cited By SCOPUS : 12
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