Uniform Coatings for Cylindrical Parts

Deposition Sciences Inc. (DSI)

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Obtaining uniform coatings on tubes and cylindrical parts is inherently challenging due to the line of sight nature of most thin film deposition processes, but can be accomplished in sputtering by utilizing innovative tooling techniques. Tubes and cylinders are used in a range of applications, including solar simulation chambers for product durability and lifetime testing. High intensity xenon arc lamps are used in most weathering chambers, as the lamp’s output closely simulates the solar spectrum. Some xenon spectral lines in the infrared are much more intense than the solar spectrum at the same wavelengths, causing excessive heating during accelerated testing and therefore need to be filtered out.

Because the xenon source is a long, thin tube, a common approach to filtering out infrared is to surround the lamp with a coated cylindrical substrate. This keeps the angle of incidence of light from the lamp at near normal at all points on the filter envelope. However, producing a uniform coating around the entire outside circumference of a highly curved tube is problematic in most thin film deposition techniques. The relatively long mean free path of the coating material molecules causes deposition to occur in a line of sight from the material source. Highly curved parts can become more thickly coated at their center, and thinner on other areas. Uneven coating thickness on cylinders and tubes can be avoided by continuously rotating the parts during deposition.

Addressing this common deposition problem, DSI engineers developed customized tooling for their reactive sputtering system to produce a uniform coating around the entire circumference of cylinders. In the custom-made tool, each tube is held by its end on a rod that rotates during the coating process. Synchronized rotation with the chamber’s drum during sputtering allows consistent coating exposure for every part of the tube’s outer surface.

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