CHARACTERIZATION OF TiN, CrN AND (TIXCR0.6-X)N 0.4 COATINGS AND THEIR TRIBOLOGICAL BEHAVIORS SLIDING AGAINST EPOXY MOLDING COMPOUND

Abstract

Epoxy molding compound (EMC) is a commonly used material in IC encapsulation. During encapsulation, the surface of molding tools suffers serious wear caused by rubbing of EMC. In view of the trend of increasing filler percentage, the wear problem on processing tools will become more significant. For study on wear resistance improvement of molding tools in this thesis, TiN, CrN and (TixCr0.6-x)No.4 coatings were deposited on tool steel substrate by physical vapour deposition (PVD) method in an unbalanced magnetron sputtering system. Coating characterization were done using analytical tools, such as SEM, GDOS, XRD and Nanoindenter. Tribological study was performed using a pin-on-disk tribo-tester. The disk was made of coated and uncoated tool steel, while the pin was made of cured EMC material. The normal load of 250 gf was applied on the pin in wear test. To compare wear performance of TiN, CrN coated and uncoated tool steel, wear tests were conducted at sliding speeds of 5, 12, 20 and 30 cm/s respectively. The results show that TiN coating yields much lower values of friction coefficient but a higher disk wear rate than CrN coating at all the tested sliding speeds. The tribological behaviors of ternary (TixCr0.6-x)No.4 coating with Ti/Cr ratio set at 0.5, 1.0 and 2.0 were studied at a sliding speed of 12cm/s. The wear resistance of these coatings was found to increase with increasing Cr content. Coating characterization and high temperature oxidation study showed that tribological properties of these coatings are related to high temperature oxidation resistance. High temperature oxidation tests were performed on all the PVD ceramic coatings using a thermal mechanical analyzer (TMA) and the oxidized surfaces were examined using Raman microscopy. The results showed that Ti0 2 is dominant in the oxidized surface of Ti-rich coatings. This is consistent with the findings that the wear ebris collected from TiN coating sliding against EMC pin in atmospheric condition consists mostly of TiO2. Oxidation-induced damage of TiN coating was confirmed by tests that ran this coating sliding against EMC pin in N2 and atmospheric environment separately. It was concluded that the formation of TiO 2 deteriorates the wear performance of titanium-containing coating during unlubricatecl sliding. The results also showed that there is a strong compositional dependence of tribological behaviors for these ternary coatings. In view In view of the practical need of actual molding process, the present study demonstrated that CrN is a suitable coating for molding machine components. The ternary (TixCr0.6-x)No.4 coating has potential to be a useful tribological coating. Such a coating can possess high hardness and high chemical inertness and therefore high wear resistance if optimal deposition conditions and coating composition can be achieved. TiN coating is the least suitable as a tribological coating deposited on molding machine components for epoxy molding material (EMC).