Sequential deposition of copper/alumina composites

Ceramic-metal composites have drawn considerable interest due to their mechanical, thermal and wear-resistant capabilities. High temperature processing of these materials when they are employed in electronic circuitry is not desirable, since elevated temperatures can irreversibly affect physical properties of the produced components. Wet chemical methods have potential advantages because they do not require thermal processing. Co-deposition of ceramic particles in metal plating baths has been extensively investigated during the past decades [1, 2]. However, the ceramic particle concentration in co-deposited materials was usually limited to below 30 vol.%. Electrophoretic Deposition (EPD) is a technique, which is capable of producing ceramic coatings. Various ceramics and metals have been deposited from aqueous and organic suspensions [3]. Due to the hydrol-ysis of water, bubbles are formed on the electrodes during the aqueous EPD process. Using an organic suspension solves this problem. Ceramic coatings have been prepared in organic solvents, such as alcohol and ace-tone. Since the coatings produced by EPD are porous, it is possible to impregnate the ceramic skeleton with metals by a post-EPD electroplating (EP) process. Only a few publications have described this approach. Shrestha et al. [4] have prepared Ni/Al 2 O 3 and Ni/BN coatings by this method, forming composites with particle concentration as high as 67 vol.%. In the present work, the authors studied Cu/Al2O3 coatings by the sequential EPD-EP deposition method. First, a layer of Al2O3 was produced by the EPD method. The kinetics of the EPD was studied to control the thickness of the deposited ceramic layer. After EPD, the ceramic coating was dipped into a copper plating bath for impregnation. The resultant deposited coatings were characterized by Scanning Electron Microscope (SEM). Al 2 O 3 particles (Alcoa A-16SG) of 0.4 μm typical size were used for EPD. The acetone-based suspension solvent contained n-butylamine, which was added to increase particle charging. The suspension was made by mixing 220 ml of acetone (Fisher Scientific), 20 g Al 2 O 3 and differing amounts of n-butylamine (Fisher Scientific). A Brookfield DV PRO II+ viscometer was used to measure the viscosity in order to evaluate the influence of the n-butylamine concentration on viscosity. The spindle shear rate was set to 100 rpm, while the temperature was maintained at 19.8 °C. The experimental results demonstrating the dependence of viscosity on the n-butylamine volume concentration are shown in Fig. 1. According to Zhao [5], 8 vol.% concentration of n-butylamine gives the …