Effect of the Saccharin Concentration on Electrodeposition of the Fe-Ni Alloy

Abstract

The FMM (Fine Metal Mask) used in the OLED display manufacturing process is a metal sheet with holes formed to allow the deposition of diode material only in the sub-pixel area. To prevent deformation and misalignment of the FMM (Fine Metal Mask) caused by heat during the RGB organic deposition process, an Invar plate with a thermal expansion coefficient (CTE) close to 0 is used. The Invar sheet applied to the current FMM is manufactured through a metallurgical process, and its final thickness after rolling is 20 micron. However, due to limitations in reducing thickness with the rolling process, for manufacturing FMM with a thickness of under 10 micron for next-generation high-resolution (UHD-level) displays, the bottom-up electroplating process is suitable. However, to maintain the shape of the electroplated Invar sheet while ensuring commercial-grade low CTE, heat treatment at temperatures exceeding 600℃ for an extended period is required, utilizing thermo-mechanical processing methods. If uniformity in the microstructure composed of nano-grains is ensured in the electroplated Invar alloy in the As-deposited, it is possible to increase the efficiency of the process by reducing the heat-treatment processing cost.Therefore, in this study, we investigated the microstructural evolution in the Invar alloy by controlling the surface stress of the electroplated layer during pre-plating. We controlled the key additive, saccharin, in the Fe-Ni alloy electrolyte to assist the diffusion of iron and nickel ions. By examining the relation between microstructural uniformity, determined by the plated layer, and CTE, we propose optimized process conditions for the pre-plated Invar sheet.