The development of Cr-N based coatings to tackle the mold sticking problem of IC packaging industry


Student thesis: Master's Thesis

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  • Wai Lun CHENG


Awarding Institution
Award date15 Feb 2013


The heavy sticking force between the mold surface and the epoxy molding compound (EMC) is a well-known problem in the integrated circuit (IC) injection molding industry. In addition, epoxy resin, which comprises glass fiber fillers and chloride-based chemical additives, causes serious erosion to the mold surface. Therefore, coatings with low surface free energy as well as high wear and corrosion resistance are required. In this study, chromium nitride (Cr-N)-based coatings deposited using the physical vapor deposition technique were used as a base to mitigate this problem. Cr-N coatings were first deposited with different optical emission monitor (OEM) ratios and then investigated in terms of structure, mechanical properties, wear resistance, corrosion resistance, and surface free energy. Mixtures of CrN or Cr2N phase in Cr-N coatings were determined through XPS and XRD analyses. The mechanical properties and surface free energies of the Cr-N coatings were close even with different OEM ratios. Cr-N deposited at 45% OEM ratio had the highest corrosion resistance and the best combination of performance in terms of surface free energy, corrosion, and wear resistance among the Cr-N coatings. Therefore, 45% OEM ratio was selected for subsequent Cr-Ni-N development, and different nickel contents were doped into the Cr-N coating by varying the CrNi target current during deposition. The effect of Ni addition on the structure and properties of Cr-Ni-N coatings was investigated. The Cr-Ni-N coatings comprised Cr2N, CrN, and a mixed metallic phase. The addition of an appropriate Ni content (20 at.% to 30 at.%) to Cr-N coating produced high wear performance. In addition, the corrosion resistance was also better than that of PVD Cr by one order of magnitude. The release forces between the coatings and EMC were examined using an in-house designed shear test rig. Cr-Ni-N coatings (Ni: 20 at.% to 30 at.%) show the lowest release force compared with PVD Cr and Cr-N coatings because of low surface free energy. However, the addition of Ni also changed the coating surface roughness. No conclusive relationship between the coating release force and Ni content can be deduced from this study.

    Research areas

  • Protective coatings, Nitrides, Molding (Chemical technology), Chromium compounds, Microelectronic packaging