Characteristics of the Fine Grained CVD Diamond Film and its Industrial Applications. K. Kazahaya, A. Yamakawa and T. Fukunisi

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1 Key Engineering Materials Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Characteristics of the Fine Grained CVD Diamond Film and its Industrial Applications K. Kazahaya, A. Yamakawa and T. Fukunisi A.L.M.T. Corp., Koutaka Aza Kuroishi, Takino, Katou-Gun, Hyogo, Japan Keywords: Fine-Grained Diamond Films, Tool for Semiconductor Package Processing Abstract. A fine grained film was coated onto a cemented carbide alloy by the hot filament chemical vapor deposition. The grains of the film were less than 1µm in diameter. The surface of the film is very smooth with a roughness value of 0.5 µm in R max. The surface roughness of the aluminum alloy (ADC12) machined using an end mill coated with this fine grained was 5 µm in R max. This is smoother than the one using commercial, coarse grained, coated end mills. A semiconductor packaging tool coated with the fine grained did not adhere to solder, in contrast to the conventional cemented carbide tool. The new coating also extended the tool life. Introduction Diamond is applied widely in industry because of it s excellent hardness, adhesion resistance, heat conduction, corrosion resistance and optical characteristics. Since the development of the chemical vapor deposition (CVD) method of coating thin film, the applications of have widened. Diamond-coated cutting tools are one typical application. Such tools are suitable for machining Al-SiC alloy and high-silicon aluminum alloys, hard carbon, green ceramics and carbon fiber reinforced plastic (CFRP), and provide high cutting performance and long tool life. However, the tools suffer from unevenness on a micrometer scale due to the edges of particles on the film surface. In the cutting process, this unevenness is transferred to the surface of the work piece, resulting in degraded surface roughness in precision applications. In addition, the metal removed during machining accumulates at these grain edges on the film to exaggerate this unevenness, leading to further degradation of machining precision and delamination of the film. In light of this, the present authors developed a method for producing fine-grained film on a cemented carbide substrate, and were successful in producing a film composed of particles of less than 1µm in diameter. In this article, the authors evaluate the characteristics of the fine-grained film, and its suitability for various industrial applications. Experimental Methods Deposition of Fine-Grained Diamond Film. Diamond film was deposited on cemented carbide by a hot-filament CVD method, as shown in Figure 1.Commercial cemented carbide composed of WC (diameter 1µm) and Co (concentration 5wt%) was used as a substrate (H1, Sumitomo Electric Industries, Ltd.). Deposition was performed for 6h using a W filament in a methane-hydrogen atmosphere. The filament and substrate temperature were 2200ºC and 850ºC, as measured using a two-color pyrometer and alumel-chromel thermocouple, respectively. CH 4 +H 2 W filament substrate Figure 1: Schematic illustration for hot filament CVD method. Evaluation of Film Characteristics. The characteristics of the fine-grained film were evaluated in terms of grain size, the surface roughness, crystallinity, organization of the cross section, All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (# , Pennsylvania State University, University Park, USA-19/09/16,01:19:30)

2 554 Advances in Abrasive Technology VI wear resistance, and sliding characteristics. The grain size was measured by scanning electron microscopy (SEM), and the surface roughness was measured using a needle-type surface roughness tester. The crystallinity was evaluated by Raman spectroscopic analysis. The organization of the cross section was observed by SEM using a cut and polished sample subsequently etched with hydrogen plasma. In hydrogen plasma treatment, the temperature of the substrate was maintained at 850 C for 0.5h. The wear resistance was evaluated by aggressive wearing of the film using a shot blaster at 100kPa with SiC (#800) abrasive. The substrate was set at a distance of 50mm from the nozzle, and the time to expose the substrate was measured as the wearing indicator. The sliding characteristics were evaluated by the pin-on-disk method, and frictional coefficients for two pin materials (SUJ2, Si 3 N 4 ceramic) were measured. The pin was loaded at 1N, and the pin was rotated at 500rpm for a total of 10,000 revolutions. Results and Discussion Morphology and Characteristics. The thickness of the fine-grained produced in this experiment was 6µm. The outward appearance was lustrous despite the coating because the mirror surface of the substrate was maintained. Figures 2 shows SEM images of the surface of the fine-grained film and the coarse-grained film on the market. The film produced in this experiment is composed of grains of less than 1 µm in diameter. The surface roughness of the two films is compared in figure 3, along with the evaluation for the polished cemented carbide used as the substrate. The surface roughness of the present film was R max =0.50µm, while that for the commercial film was R max =1.55µm. Figure 4 shows the Raman spectrum for the fine-grained film. A sharp peak due to is seen at 1333cm -1, and this assignment was confirmed in the XRD patterns of the film. This verifies that the film made in this experiment was indeed. (a) (b) 10µm 10µm Figure 2: SEM images of the surfaces of film. (a)fine-grained one (b)coarse-grained one on the market Rmax(µ) Fine-grained coarse-grained Substrate (cemented carbide) Figure 3: Comparison of the surface roughness of the samples.

3 Key Engineering Materials Vols D-band G-band Figure 4: Raman spectrum of the fine-grained film. Film Structure. Figure 5 shows SEM images of a cross section of the fine-grained film and the coarse film. The image was taken at a point 3µm from the substrate. The grain boundaries are emphasized due to selective etching during hydrogen plasma treatment. The fine-grained film is organized on a much smaller scale than the commercial film, and does not have a laminated structure. (a) (b) 100nm 100nm Figure 5: SEM images of a cross section of the films. (a)fine-grained one (b)coarse-grained one Wear and Sliding Characteristics. Figure 6 shows the wear resistant characteristics of various films, as evaluated by shot blasting. Abrasive wear was not observed in the fine-grained film, similar to the commercial coarse-grained film, exhibited very high wear resistance, more than 3 times higher than the other hard films. Figures 7 and 8 show the sliding characteristics of these films as determined by the pin-on-disk method using SUJ2 or Si 3 N 4 ceramic as a pin. In this experiment, we used a commercial film after polishing, because if we use no-polished film, the frictional coefficient become too high due to the unevenness on the surface. The frictional coefficient of the fine-grained film for both pin materials is lower than the cemented carbide alloy and close to that of -like carbon (DLC) and polished commercial film. As above, fine-grained film has low frictional coefficient even though without polishing. This property is caused by flat surface and adhesion resistance of the fine-grained film. Application to Cutting Tools. Figure 9 shows the surface roughness of a work piece machined using a cutting tool (ø8-mm end mill with parallel shank) coated with the fine-grained. The work piece was a sample of ADC12 alloy (aluminum-12% silicon), machined under dry conditions. The machined surface roughness was R max =5µm, while that for the commercial coarse-grained coated tool was 9µm. This excellent cutting performance is attributable to the microscopic

4 556 Advances in Abrasive Technology VI evenness of the fine-grained film in comparison to the commercial product, and excellent adhesion resistance. This fine-grained film produces a smoother finished surface for precision applications, and therefore represents a valid improvement over previous film technologies. no wear Blasting Time(s) fine-grained coarse-grained DLC TiN [Testing condition] Abrasive:#800SiC Pressure:100kPa Distance:50mm Evaluation area:2mm x 2mm Figure 6: Wear resistance of the films evaluated by the shot blasting. Frictional coefficient fine-grained polished Substrate DLC (cemented carbide) [Testing condition] Load force:1n Revolution speed:500rpm Frequency:10000 Pin:SUJ2 Figure 7: The frictional coefficient of the samples.(pin:suj2) Frictional coefficient fine-grained polished DLC Substrate (cemented carbide) [Testing condition] Load force:1n Revolution speed:500rpm Frequency:10000 Pin:Si 3 N 4 Figure 8: The frictional coefficient of the samples.(pin:si 3 N 4 )

5 Key Engineering Materials Vols Rmax(m) fine-grained coarse-grained [Machining condition] Cutting speed:400m/min Feed rate:0.04mm/teeth Axial depth:0.05mm Tool:8 end mill Workpiece:ADC12(Al-12%Si) Figure 9: The machining surface roughness of the coated tools. Application to Semiconductor Packaging Tool. The fine-grained film was applied for use on a semiconductor packaging tool, which is used to cut or form the outer lead on IC or LSI packaging to allow it to sit easily on the substrate. The lead is plated with solder, and when a polished cemented carbide alloy tools are used, this solder adheres to the tool and degrade the processing precision. Also, when commercial coarse-grained coated tools are used, similar problem happens because of an evenness of the film. Polished are valid, but the type of the tools are limited because these tools have to be polished even though any shapes. Nowadays, cemented carbide tools are used, and removed solder regularly. Thus, the solution to this problem is demanded by the semiconductor industry. Figure 10 shows the results of an evaluation of the adhesion resistance against solder for a tool coated with fine-grained and an uncoated tool. A 100%-Sn soft solder was used as the pin in the pin-on-disk test, and the pin was revolved a total of 1000 times under 1N force at 500rpm. As the images show, no solder adhered to the -coated disk, leaving only solder dust (dark material), while solder readily adhered to the cemented carbide alloy, and no WC can be seen. After ultrasonication in acetone for 10 minutes, the dust on the fine-grained film was effectively removed, whereas the solder remained adhered to the cemented carbide alloy. This confirms the excellent adhesion resistant of the fine-grained film with respect to solder. The film was then applied to a lead-cutting punch and die, a tool used for the cutting a lead frame to detach a package from the package frame. The processing accuracy remained high even after 1,000,000 shots, and it was not necessary to remove solder at any time during this number of shots. In contrast, the cemented carbide tool became unsatisfactory after 30,000 shots, and required a solder removal. Conclusions The characteristics of fine-grained deposited by hot-filament CVD on cemented carbide were examined with respect to possible industrial applications. The film was found to be composed of small particles of less than 1µm in diameter, and to have excellent wear and adhesion resistance. An aluminum alloy work piece machined using an end mill coated with the fine-grained film had a lower surface roughness than when a commercial -coated tool was used. The fine-grained film also had excellent adhesion resistant to solder, and the film was examined as a coating for a lead-cutting punch and die for semiconductor packaging. The processing accuracy remained high even after 1,000,000 shots, without the need for solder removal.

6 558 Advances in Abrasive Technology VI Fine-grained Cemented carbide alloy (a) (b) (c) (d) Figure 10: Adhesion resistance against solder of the fine-grained film. (a) fine-grained (after test) (b)cemented carbide(after test) (c)fine-grained (after ultrasonication) (d)cemented carbide (after ultrasonication) References [1] Y. Matsumoto, S. Kawai, K. Tomari and K. Kazahaya: A.L.M.T. Technical Review, 2001, p. 27. [2] A.K. Gangopadhyay, P.A. Willermet, M.A. Tamor and W.C. Vassell: Tribology International, Vol. 30 (1997), p. 9. [3] S. Ri, H. Yoshida and H. Watanabe et al: The 10 th International Symposium on Advanced Materials. [4] Y. Murakami and H. Hanyu: Journal of the Japan Society for Abrasive Technology, Vol. 46 (2002), p. 14.