Characterization of the Contamination Factor of Electroless Ni Plating Solutions on the ENIG Process
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The electroless nickel immersion gold process often produces defects, such as pinholes and black pads that can cause brittle fractures at the interface between the solder and metal pad. Contamination in electroless Ni plating solutions with increasing metal turn over (MTO) is believed to be one of the causes of the formation of surface defects. MTO means indirectly Ni bath life, with ‘‘0 MTO’’ indicating a freshly plating bath and ‘‘2 MTO’’ an aged plating bath, which is supplemented twice with the initial amount of metallic salts and the reducing agent. In this study, surface defects on the Ni-plated layer were investigated to understand the correlation between the MTO solutions and defect factors by solder resist (SR) dissolution. The characteristics of the contaminated MTO solutions were analyzed by total organic carbon and liquid chromatography mass spectrometry (LC-MS). LC-MS detected the component (melamine) of the hardener of the SR at 2.14 ppm in the 2 MTO, and 2.52 ppm in the 2.5 MTO solutions. Electroless nickel plating was conducted in a 0 MTO solution with hardener addition. Pinholes were observed in solutions containing more than 2 ppm of a hardener. In particular, the content of phosphorus in the defective area was higher than that in the non-defective area. Consequently, as the MTO solution increased, the hardener was dissolved in the Ni solution, which caused defects in the nickel surface layer, such as pinholes and black pads.
KeywordsElectroless nickel immersion gold surface defects solder resist black pad pinhole hardener
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- 14.Z. Mei, M. Kaufmann, A. Eslambolchi, and P. Johnson, in Electronic Components & Technology Conference, 48th IEEE (1998), pp. 952–961Google Scholar
- 15.W. Li, in Electronic Packaging Technology (ICEPT), 16th International Conference on IEEE (2015), pp. 538–541Google Scholar
- 17.Y. Ono, A. Goto, A. Niki, and M. Asai, Solder resist composition and printed circuit boards, in, U.S. Patent No 6,217,987 (2001)Google Scholar
- 18.G.O. Mallory and J.B. Hajdu, Electroless plating: fundamentals and applications (Orlando: American Electroplaters and Surface Finishers Society, 1990), pp. 3–11.Google Scholar