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Substrate Defect Detector

IP.com Disclosure Number: IPCOM000041031D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Bowen, AJ: AUTHOR [+2]

Abstract

One of the problems which can appear during the manufacture of magnetic disk substrates is the presence of small pits, scratches, and diamond turn pull-outs less than 10 microns in width. The above substrate defect detector determines the size of defects located on magnetic disk substrates and plated magnetic disks. The detector utilizes low power laser light to detect incongruities on disk surfaces.

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Substrate Defect Detector

One of the problems which can appear during the manufacture of magnetic disk substrates is the presence of small pits, scratches, and diamond turn pull- outs less than 10 microns in width. The above substrate defect detector determines the size of defects located on magnetic disk substrates and plated magnetic disks. The detector utilizes low power laser light to detect incongruities on disk surfaces.

The detection technique used in this substrate defect detector system permits accurate sizing of the detected defects. It provides more accurate information about the size of defects than existing methods due to its reduced dependence on the defect geometry. The detection technique uses a low power (2 mW) laser beam which is focused to a 5 micron diameter spot on the surface of a spinning disk.

When no incongruities are within the laser spot on the disk, the incident light is reflected by the disk toward a PIN diode. The PIN diode produces a current which is proportional to the intensity of the light which falls on it.

When a defect passes through the laser spot, light is scattered away from the PIN diode. This causes a decrease in the current produced by the diode which is proportional to the amount of light which was deflected by the defect. Thus, the current from the PIN diode can be calibrated and used to determine the size of a defect on a disk surface.

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