Method and apparatus for testing pattern of a printed circuit board

• US 4,700,225 A
• Filed: 09/30/1986
• Issued: 10/13/1987
• Est. Priority Date: 10/02/1985
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Saito, Keiya, Hara, Yasuhiko, Karasaki, Koichi, Sase, Akira
• Primary Examiner(s): Britton, Howard W.
• Application Number:
  US06/913,242
• Time in Patent Office: 378 Days
• Field of Search: 358/106, 358/101, 358/107, 358/93, 358/225, 382/8
• US Class Current: 382/149
• CPC Class Codes: G01R 31/2806 Apparatus therefor, e.g. test stations, drivers, analysers, conveyors G01R31/2805, G01R31/281, G01R31/2818 take precedence
• CPC Class Codes: G01R 31/309 of printed or hybrid circuits or circuit substrates

Abstract

A method and an apparatus for testing the pattern of a printed circuit board, comprising a stroboscope for emitting intermittent light synchronously with the feed velocity of the printed circuit board; a condenser lens for gathering the intermittent light emitted from the stroboscope and irradiating the gathered light to the printed circuit board; a filter for converting the light of the stroboscope to exciting light; a half mirror for reflecting the exciting light gathered by the condenser lens and converted by the filter, then projecting the reflected light upon the printed circuit board perpendicularly thereto, and passing the excited fluorescent light from the substrate of the printed circuit board; an imaging lens for forming an image of the fluorescent light passed through the half mirror; another filter for eliminating any other light than the fluorescent light out of the entire light passed through the half mirror; a TV camera for picking up the fluorescent image formed by the imaging lens; a memory for storing the preceding-frame pattern video signal obtained from the TV camera with the stroboscope turned on and attenuated by an amount corresponding to the afterimage component; a circuit for subtracting the attenuated stored pattern video signal from the present-frame pattern video signal obtained from the TV camera with the stroboscope turned on; a circuit for generating a reference pattern; and a circuit for producing a negative pattern of the wiring pattern from the output signal of the subtracting circuit and comparing the negative pattern with the reference pattern. In this invention, the image of the printed circuit board set on the table in continuous motion is picked up by the TV camera without any harmful influence of the afterimage so that the printed circuit board can be properly checked to ascertain whether the wiring pattern thereof is normal or not.

Claims

1. A method of testing the pattern of a printed circuit board, comprising the steps of:

emitting intermittent light from a stroboscope synchronously with a feed velocity of said printed circuit board;

gathering said intermittent light by a condenser lens;

converting said light to exciting light through a filter;

reflecting said exciting light by a half mirror to project the same upon said printed circuit board perpendicularly thereto and passing through said half mirror the fluorescent light emitted from the substrate of said printed circuit board;

forming an image of the fluorescent light passed through said half mirror by means of an imaging lens while eliminating any other light than the fluorescent light through another filter, thereby passing therethrough the fluorescent image;

picking up the fluorescent image by a TV camera;

attenuating, by an amount corresponding to the afterimage component, the preceding-frame pattern video signal obtained from said TV camera with said stroboscope turned on, and storing the attenuated pattern video signal in a memory means;

subtracting the stored attenuated pattern video signal from the present-frame pattern video signal obtained from said TV camera with said stroboscope turned on, thereby producing a negative pattern of the wiring pattern; and

comparing said negative pattern with a reference pattern to check whether the wiring pattern of said printed circuit board is normal or not.

2. An apparatus for testing the pattern of a printed circuit board, comprising:

a stroboscope for emitting intermittent light synchronously with a feed velocity of said printed circuit board;

a condenser lens for gathering the intermittent light emitted from said stroboscope and irradiating the gathered light to said printed circuit board;

a filter for converting the light of said stroboscope to exciting light;

a half mirror for reflecting the exciting light gathered by said condenser lens and converted by said filter, then projecting the reflected light upon said printed circuit board perpendicularly thereto, and passing the excited fluorescent light from the substrate of said printed circuit board;

an imaging lens for forming an image of the fluorescent light passed through said half mirror;

a filter for eliminating any other light than the fluorescent light out of the entire light passed through said half mirror;

a TV camera for picking up the fluorescent image formed by said imaging lens;

a memory means for storing the preceding-frame pattern video signal obtained from said TV camera with said stroboscope turned on and attenuated by an amount corresponding to the afterimage component;

a means for subtracting said attenuated stored pattern video signal from the present-frame pattern video signal obtained from said TV camera with said stroboscope turned on;

a means for generating a reference pattern; and

a means for producing a negative pattern of the wiring pattern from the output signal of said subtracting means and comparing said negative pattern with said reference pattern.

3. The apparatus as defined in claim 2, wherein said half mirror consists of a dichroic mirror.

4. The apparatus as defined in claim 2, further comprising an A/D converter for converting the output video signal of said TV camera to a digital video signal.

5. The apparatus as defined in claim 4, further comprising a multiplier for multiplying the digital video signal of said A/D converter by an attenuation factor, wherein the output of said multiplier is stored in said memory means.