Abstract
In printed electronics, laser ablation is used to repair defective patterns on transparent, flexible, and thin films, using high-power lasers. The distance between the film surface and laser focus is sensitive to changes as the narrow focus depth of the lens is the range of tens of microns. However, a film fixed on a conductive vacuum chuck (CVC) is always curved, owing to chucking bending; thus, laser focusing must be locally performed before ablation. Therefore, this study proposes a non-contact measurement method for the surface flatness of a transparent and thin film, to compensate for laser defocusing in a large area. The surface flatness was obtained using camera-focus points on the porous surface of the CVC. The focus points were interpolated to achieve a smooth and continuous surface flatness for chucking bending. A laser distance sensor was used to verify the surface flatness from the proposed method. The surface flatness was used to inspect the printed patterns, and to perform laser ablation on the film. The proposed method is advantageous for large-area laser ablation and is expected to become indispensable for repairing machines in printed electronics.
Highlights
The conventional concept of printed electronics (PEs) comprises the fabrication of circuits and patterns on a thin substrate by injecting conductive ink [1]
The defocusing of laser ablation owing to the chucking bending of the flexible and thin film can be reduced by the surface flatness
The surface flatness of the film was estimated from that of the conductive vacuum chuck (CVC) based on a non-contact and optical method considering the transparency, thinness, and printed patterns of the film
Summary
The conventional concept of printed electronics (PEs) comprises the fabrication of circuits and patterns on a thin substrate by injecting conductive ink [1]. In laser ablation for a large area, the quality of the beam focus is dependent on the surface flatness, thickness, and bending radius of the film. Choi proposed a laser confocal reflection method for thickness measurements of large areas [14]. His method was applied to a dual-layer hard coating on a PET film. Bornemann presented thickness measurements for large-area and multi-layer printed devices using. Studies on the surface flatness values of transparent and thin films in PEs are relatively rare compared to the above-noted thickness measurements. The first peaks of a non-contact thickness measurement imply distances from the ideal film surface; the first peaks of a large area can be converted to a surface flatness.
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