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January 2017 • SMT Magazine 59 Figure 7: A model depicting the covering process of Pd plating film on the Ni plating film. solving during immersion plating of Au. How- ever, in the case of electroless Ni/Au film (Figure 9b), the surface of the electroless Ni was found to have dissolved evenly during the immersion gold plating. The cross-sectional views of the plating film and solder joint interface for various Pd thick- nesses are shown in Figure 10. In the case of electroless Ni/Au film (Figure 10a), the surface of electroless Ni was corroded by the immersion gold plating. IMC layers were formed at the in- terface of solder and the corroded electroless Ni during the reflow process. The corroded electro- less Ni layer is the cause of the poor adhesion at the Ni/IMCs interface. Therefore, the brittle fracture may easily occur in the case of electro- Figure 8: SEM photographs of surface morphology of the electroless Ni after the dissolution of Au or Pd. (a) electroless Ni/Pd/Au; (b) electroless Ni/Au. Figure 9: TEM photographs of cross-section of the electroless plating film (a) electroless Ni/Pd/Au; (b) electroless Ni/Au. SOLDER BALL JOINT RELIABILITY WITH ELECTROLESS NI/PD/AU PLATING