Forty dot/millimeter resistive ribbon thermal print head

Abstract

A key element to printing high resolution grey level images using resistive ribbon thermal printing technology, is the ability to fabricate a high density electrode print head. To print at 40 dots/mm resolution, the print head electrodes have to be on 25 μm centers. Each electrode having a width of 15 to 17 μm. Wet etching techniques can not etch such structures in 25 μm thick tungsten. A reactive ion etching process suitable for manufacturing high resolution print heads from a tungsten sheet has been developed. Various system parameters were studied, such as gas mixtures, system vacuum pressure and applied RF power, with the goal of achieving an optimum etching process. The results identified SF6 based gas mixtures as the most suitable candidate for high volume removal of tungsten with an acceptable etch rate and edge profile. To study the print quality at 40 pel/mm, other parameters such as ink ribbon and paper surface finish were also investigated. An ink layer thickness and a paper were selected to match the quality of the high resolution print head. The electric power requirements to print single pel features repeatedly was studied.