Thermal transfer printing technique for electrode patterning in cofired ceramic multi-layer devices
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A new mask-less electrode patterning method using a thermal transfer printing technique was investigated. Thermal ink ribbons were prepared, which included more than 50 vol. % conductive metal powder. Arbitrary electrode patterns were designed with a computer and printed out on a ceramic green sheet with a serial thermal printer. The ceramic green sheets with printed electrode patterns were stacked up and cofired to obtain a multi-layer ceramic capacitor.
I. INTRODUCTION A fine patterning technique is indispensable in fabricating electronic ceramic devices using thick films. Screen printing has been widely used for electrode patterning, and recently some new mask-less printing technologies have been introduced. Drumheller reported that a writing system with a pen controlled by a computer had an advantage over conventional screen printing, eliminating most of the normal phototype design-to-test turnaround time, along with most of the cost.1 Isozaki et al. applied electrophotography to fabricate a glassceramic substrate with a low dielectric constant.2 They also emphasized that the direct thick film writing system is advantageous in that it shortens the fabrication period in custom-made production, since a direct interface between a computer and a printer permits design and modification of patterns. When choosing a mask-less printing technology for application to electrode printing in cofired multilayer devices with high-density ceramics, neither the pen writing system nor electrophotography is sufficient. The starting material for the electrode in the devices is metal powder which sinters at almost the same temperature as the ceramic powder. An ink including such metal powder tends to cause choking of the writing pen tip. Inks consisting of dissoluble dyes are preferable for the pen writing system. On the other hand, in the cofiring multi-layers, it is desirable that volume percentages of the metal in the patterned electrode and of the ceramic in the green sheet are equally high, because their contractivities should be equally low. However, the amount of metal powder in a toner, which is a key material in electrophotography, cannot be so large since electrostatic chargeability of the toner must be maintained. The thermal transfer printing technique is one of the digital marking technologies that are used in a printer for a personal computer or in a bar code printer. It J. Mater. Res., Vol. 9, No. 5, May 1994
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is an image-forming process in which a coated layer including carbon black and polymer in an ink ribbon is melted and transferred onto the paper surface by thermal dot energy supplied from a thermal head in the printer. This technique has the advantages of printability on plain paper, environmental safety, high reliability, and small equipment size.3 It also has the same advantage of being easily controlled by a computer as the other maskless printing technologies described above: an ease in designing and modifying patterns. Furthermore, anyone can easily
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