Browse Prior Art Database

Optical Inspection System

IP.com Disclosure Number: IPCOM000051541D
Original Publication Date: 1981-Feb-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Strope, DH: AUTHOR [+4]

Abstract

Inspection of printed circuit clearance holes for imperfections can be performed by a scanning linear array of charge-coupled photodiodes in conjunction with a data display and processor.

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Optical Inspection System

Inspection of printed circuit clearance holes for imperfections can be performed by a scanning linear array of charge-coupled photodiodes in conjunction with a data display and processor.

Referring to Fig. 1, a printed circuit substrate 1 is supported on an X-Y indexing table 2 and is illuminated by light sources 3 through lenses 4. Reflected light is focussed through objective lens 5 onto a scanning linear array 6 of charge-coupled photodiodes. The photodiodes are attached to a stationary support 7 housing array control logic, video amplifiers and analog-to-digital converters. A single light source and beam splitter are used to examine flat surfaces and bottoms of holes.

A block diagram of the inspection system is shown in Fig. 2. Light incident on scanner 6 generates photocurrent that is integrated and stored as a charge on the capacitance of each photodiode. Antiblooming gates limit the charge. At the end of each interrogation period, which may be one or more steps of the X-Y table 2, the stored charges are simultaneously switched through transfer gates to two analog shift registers. Odd and even diodes are switched to different shift registers. During the next interrogation period, the shift registers are read out with alternate odd and even bits through preamplifiers to analog to digital converter (ADC) 8, which determines whether the charge level of each diode represents a black or white level. The ADC also provides timing signals...