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Retardation of Massive Spalling by Palladium Layer Addition to Surface Finish

팔라듐 표면처리를 통한 Massive Spalling 현상의 억제

  • 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)
  • 이대현 (고려대학교 신소재공학부) ;
  • 정보묵 (고려대학교 신소재공학부) ;
  • 허주열 (고려대학교 신소재공학부)
  • Received : 2010.06.29
  • Published : 2010.11.25

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

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