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Measurement of Particulate Contamination in Substrates

IP.com Disclosure Number: IPCOM000042721D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Bartkus, EA: AUTHOR

Abstract

Two layers of a plastic film are pressed onto a nonreflective platform. Transmitted polarized light is directed onto the layers. Substrate film asperities can be distinguished from particulate debris wound into the film. Particulate contamination in rolls of biaxially oriented polymer film, such as polyethylene terephthalate used as substrate for flexible magnetic recording media, can be measured. A sample comprising two layers of the film is obtained from the roll exterior, taking care not to expose the facing surfaces to ambient atmosphere, which could add particulates to those surfaces. This sample is pressed onto an opaque, nonreflective surface and illuminated with monochromatic, e.g., sodium, light.

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Measurement of Particulate Contamination in Substrates

Two layers of a plastic film are pressed onto a nonreflective platform. Transmitted polarized light is directed onto the layers. Substrate film asperities can be distinguished from particulate debris wound into the film. Particulate contamination in rolls of biaxially oriented polymer film, such as polyethylene terephthalate used as substrate for flexible magnetic recording media, can be measured. A sample comprising two layers of the film is obtained from the roll exterior, taking care not to expose the facing surfaces to ambient atmosphere, which could add particulates to those surfaces. This sample is pressed onto an opaque, nonreflective surface and illuminated with monochromatic, e.g., sodium, light. Under low magnification, an interference fringe pattern is observed wherever the facing film surfaces are held apart, either by film asperities or by particulate contaminants. If the region showing an interference fringe pattern is viewed by transmitted polarized light (analyzer at 90 degrees, i.e., extinction, to illumination polarization plane), a characteristic birefringence pattern is observed surrounding film asperities. This pattern is absent if the interference fringes are due to a particle on the film surface. Thus, particulates wound into the roll can be distinguished from film asperities. By examining a substantial sample area, the number of particulates per unit area can be determined, in addition...