Thin Film Technology Strategic Research Programme

In the plastic molding industry, plastic parts like pager and handphone cases, plastic containers, etc. are formed in a mold by applying temperature and pressure. The transfer molding is the standard workhorse for the electronics industry. Although the transfer molding is widely used, it is far from being optimized. Mold sticking is a serious practical problem in this industry. A solution to the problem is to apply mold-releasing agents on the mold to act as a lubricant layer between the plastic and the mold. This easily results in stains and degraded surface finish. This paper investigates the effectiveness of solid thin films on reducing the adhesion between polymer and mold steel of different surface roughness. WS2, MoS2, and DLC coatings are deposited on test surfaces via unbalanced magnetron sputtering before polymer blocks are molded on and pulled apart using an Instron Machine. The force required to separate the plastic part and the mold steel is used as an indication of the stickiness. After the separation, the coating surface is also examined under microscope for stains and polymer residues. The coatings are characterized using Raman spectroscopy and contact angle measurements. Generally, the stickiness increases with initial surface roughness for all coatings. Initial test indicates that the DLC coating has the highest contact angle with water (100°) and the best antisticking properties among the samples tested, and could reduce the stickiness by 80% as compared to bare steel. YQ Fu, HJ Du and S Zhang, Curvature method as a tool to evaluate shape memory effects for TiNiCu thin films,SURFACE ENGINEERING: SCIENCE AND TECHNOLOGY II, Edited by: Ashok Kumar, Yip-Wah Chung, John J. Moore, Gary L. Doll, Kyoshi Yatsui, D.S. Misra, Feb 2002, pp 293-303. Abstract TiNiCu films were prepared by co-sputtering of a Ti55Ni45 target with a separated Cu target. Curvature method was used to measure residual stress and evaluate shape memory effects. Results showed that for samples deposited at room temperature, large tensile stress was found in the deposited films. Post-annealing of the above samples at 923 K for 1 hour could significantly reduce the residual stress. The residual stress of samples deposited at 723 K was quite low. Upon heating, TiNiCu films generated large tensile stress when transforming from martensite to austenite, whereas during cooling, the stress relaxed significantly when the films transformed back to the ductile martensite phase. Effects of film thickness, heating rate, annealing process and cyclic heating/cooling process on martensite phase transformation were investigated.TiNiCu films were prepared by co-sputtering of a Ti55Ni45 target with a separated Cu target. Curvature method was used to measure residual stress and evaluate shape memory effects. Results showed that for samples deposited at room temperature, large tensile stress was found in the deposited films. Post-annealing of the above samples at 923 K for 1 hour could significantly reduce the residual stress. The residual stress of samples deposited at 723 K was quite low. Upon heating, TiNiCu films generated large tensile stress when transforming from martensite to austenite, whereas during cooling, the stress relaxed significantly when the films transformed back to the ductile martensite phase. Effects of film thickness, heating rate, annealing process and cyclic heating/cooling process on martensite phase transformation were investigated. Zeng Xianting, Sam Zhang, L. S. Tan, Multilayered (Ti, Al) Ceramic Coating for High Speed Machining Applications, J. Vac. Sci. Technol. A, Vol. 19, No. 4, Jul/Aug 2001 pp. 1919-1922. Abstract A multilayered (Ti, Al) ceramic hard coating was deposited on tunsten-carbide ball-nose end mills for high-speed machining using an unbalanced magnetron-sputtering system. The process parameter dependence of the coating properties was studied. X-ray diffractometry, x-ray photoelectron spectroscopy, nanoindentation, and scratch tests were used to characterize the structural, compositional, and mechanical properties of the coatings. High hardness, up to 40 GPa; good adhesion strength, up to 100 N in scratch critical load; and high-oxidation resistance were achieved, leading to excellent performance in high-speed milling on hardened tool steel at a speed of 260 m/min. The results show that the tool life with this coating is improved by a factor of 4 or better under the testing conditions used compared to the uncoated tools. The surface finish of the machined steel achieved with this coating is also significantly better.A multilayered (Ti, Al) ceramic hard coating was deposited on tunsten-carbide ball-nose end mills for high-speed machining using an unbalanced magnetron-sputtering system. The process parameter dependence of the coating properties was studied. X-ray diffractometry, x-ray photoelectron spectroscopy, nanoindentation, and scratch tests were used to characterize the structural, compositional, and mechanical properties of the coatings. High hardness, up to 40 GPa; good adhesion strength, up to 100 N in scratch critical load; and high-oxidation resistance were achieved, leading to excellent performance in high-speed milling on hardened tool steel at a speed of 260 m/min. The results show that the tool life with this coating is improved by a factor of 4 or better under the testing conditions used compared to the uncoated tools. The surface finish of the machined steel achieved with this coating is also significantly better. S. Zhang, H. Xie, X.T. Zeng and P. Hing: Residual Stress Characterization of Diamond-like Carbon Coatings by X-ray Diffraction Method, Surface and Coatings Technology, 1999, Vol. 122 pp. 219-224 Abstract This paper presents residual stress measurements of amorphous diamond-like carbon (DLC) coatings obtained by studying the stress conditions of the substrate surface layer immediately adjacent to the coating via X-ray diffraction ( XRD) with a thin film attachment. In such a set-up, the incidence angle a at which the primary beam strikes the specimen is fixed at a glancing angle (2° in our experiments) relative to the sample surface while the detector rotates to collect the diffracted X-rays. The amorphous carbon coatings were deposited on single-crystal silicon wafers and on polycrystalline KBr substrates in an unbalanced magnetron sputtering system. The effects of substrate material and deposition parameters on the internal stresses of the coatings are discussed in detail. XRD with thin film attachment provides a new and more precise way to determine the residual stresses in amorphous coatings. Increasing the relative nitrogen flow reduces the compressive stress level of the hydrogenated amorphous carbon coatings. Under the experimental conditions studied, higher substrate bias power and sputter power densities both increased the compressive stress level. © 1999 Elsevier Science S.A. All rights reserved.This paper presents residual stress measurements of amorphous diamond-like carbon (DLC) coatings obtained by studying the stress conditions of the substrate surface layer immediately adjacent to the coating via X-ray diffraction ( XRD) with a thin film attachment. In such a set-up, the incidence angle a at which the primary beam strikes the specimen is fixed at a glancing angle (2° in our experiments) relative to the sample surface while the detector rotates to collect the diffracted X-rays. The amorphous carbon coatings were deposited on single-crystal silicon wafers and on polycrystalline KBr substrates in an unbalanced magnetron sputtering system. The effects of substrate material and deposition parameters on the internal stresses of the coatings are discussed in detail. XRD with thin film attachment provides a new and more precise way to determine the residual stresses in amorphous coatings. Increasing the relative nitrogen flow reduces the compressive stress level of the hydrogenated amorphous carbon coatings. Under the experimental conditions studied, higher substrate bias power and sputter power densities both increased the compressive stress level. © 1999 Elsevier Science S.A. All rights reserved. S. Zhang and H. Xie: Improving Adhesion of Amorphous Carbon on Cemented Carbide Through Plasma Cleaning, Surface and Coatings Technology, (113)1-2 (1999) pp. 120-125. Abstract Diamond-like amorphous carbon coatings 1 μm thick were deposited onto cemented carbide substrates by magnetron sputtering of a graphite target in argon under different substrate bias powers and chamber pressures. Scratch testing was used to assess the coating adhesion. X-ray photoelectron spectroscopy depth profiling was employed to quantify cobalt loss at the substrate surface as a function of bias power during plasma cleaning. It was found that under the same deposition conditions, the scratch adhesion strength increased with the bias power during plasma cleaning and reached a maximum at about 200 W or -210 V in terms of induced voltage. After that, further increases in bias power led to a decrease in adhesion. The increase was attributed to better cleaning of the sample surface and removal of surface cobalt while the decrease in adhesion was linked to an increase in residual stress which resulted in a different failure mechanism. Thus, an increase in the deposition power density, and therefore more severe ion bombardment, led to higher residual stress and lower adhesion. Under constant bias and deposition power, however, it was established that below a certain minimum chamber pressure spontaneous coating detachment occurs.Diamond-like amorphous carbon coatings 1 μm thick were deposited onto cemented carbide substrates by magnetron sputtering of a graphite target in argon under different substrate bias powers and chamber pressures. Scratch testing was used to assess the coating adhesion. X-ray photoelectron spectroscopy depth profiling was employed to quantify cobalt loss at the substrate surface as a function of bias power during plasma cleaning. It was found that under the same deposition conditions, the scratch adhesion strength increased with the bias power during plasma cleaning and reached a maximum at about 200 W or -210 V in terms of induced voltage. After that, further increases in bias power led to a decrease in adhesion. The increase was attributed to better cleaning of the sample surface and removal of surface cobalt while the decrease in adhesion was linked to an increase in residual stress which resulted in a different failure mechanism. Thus, an increase in the deposition power density, and therefore more severe ion bombardment, led to higher residual stress and lower adhesion. Under constant bias and deposition power, however, it was established that below a certain minimum chamber pressure spontaneous coating detachment occurs. 8. Contact Persons & Web-site address The Thin Films SRP welcomes collaboration with industries, research entities and researchers home and abroad. Please direct queries to Associate Professor Sam Zhang, Director of Thin Films SRP, School of MPE at 6790 4400 or [email protected]. Details of the program information and its research activities and capabilities can be found at its website at http://www.ntu.edu.sg/MPE/Research/Programmes/Thinfilms/