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High Resolution, High Throughput Inspection System for Sheet-Like Specimen Using X-Rays

IP.com Disclosure Number: IPCOM000049339D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 4 page(s) / 76K

Publishing Venue

IBM

Related People

Langner, GO: AUTHOR

Abstract

Medium soft X-rays for fast, large area, high resolution non-destructive and contactless inspection of sheet-like structured specimens, such as multilayered ceramic (MLC) greensheets, are employed. The use of X-rays has several advantages over the use of light optical means or E-beam tools. For example, use of X-rays permits a simultaneous inspection of both surfaces. In addition, the vacuum environment can be avoided.

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High Resolution, High Throughput Inspection System for Sheet-Like Specimen Using X-Rays

Medium soft X-rays for fast, large area, high resolution non-destructive and contactless inspection of sheet-like structured specimens, such as multilayered ceramic (MLC) greensheets, are employed. The use of X-rays has several advantages over the use of light optical means or E-beam tools. For example, use of X-rays permits a simultaneous inspection of both surfaces. In addition, the vacuum environment can be avoided.

Defects in screened patterns become evident as deviations in the mass thickness. Shorts, for instance, result in a high mass thickness of the highly X- ray absorbing molybdenum paste where there is only expected mass thickness of much less absorbing greensheet. On the other hand, conductors which are too thin, or incompletely filled via holes, or via holes plugged by low-absorbing material, result in the opposite, i.e., a lower mass thickness of the highly absorbing molybdenum paste. Judiciously choosing operating conditions to match the material (e.g., molybdenum versus Al(2)O(3)) permits small differences in the mass thickness to cause marked signal differences. For example, operating the X-ray tube in a region between 20 and 25 kilovolts permits thickness variations of a few micrometers to be readily detected.

In implementing an X-ray inspection system, conventional structure cannot be employed. In this regard, the particular requirements regarding resolution, area to be inspected and speed (the latter which prohibits step and repeat specimen movement) can only be met by the use of a special arrangement.

As shown in Fig. 1, an arrangement is provided for inspecting screened MLC greensheets using X-rays. The arrangement provides for moving specimen 1, supported by a frame 2, continuously and in close proximity to the long, narrow window 4 of a particular linear scan X-ray vidicon tube 3. As can be seen, the vidicon tube covers the entire width of the specimen. X-rays are produced in X- ray tube 11, which has a long, line-like X-ray-producing area on anode 12. In addition, X-ray tube 11 has an exit window in close proximity to the specimen, opposite to and aligned with the linear scan vidicon tube.

The specimen is scanned in a raster-scan fashion. In the X-ray vidicon tube, the electron beam is deflected along the X-ray photoconductive target by means of two deflection yokes 26 and 27 in tandem, enforcing perpendicular landing of the electrons. The specimen continuously moves by the amount of one spot size in the vidicon for each scan.

The movement of the specimen is essentially continuous but controlled in synchronization with beam deflection in X-ray pickup tube 3. The deflection signal is of the sawtooth type. The drive means accomplishing movement, a positioning sensor for sensing movement and controls therefore are shown at 17, 18 and 19, respectively, in Fig. 1. Signal son between the delivered video signal train and a sto...