Browse Prior Art Database

Fluorescent Prepreg Additive Improves Optical Inspection

IP.com Disclosure Number: IPCOM000102706D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 30K

Publishing Venue

IBM

Related People

Simpson, LL: AUTHOR [+2]

Abstract

A method is disclosed which increases the effectiveness of optical inspection tools that utilize fluorescence to discriminate between the metallic and prepreg regions of printed circuit boards.

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Fluorescent Prepreg Additive Improves Optical Inspection

       A method is disclosed which increases the effectiveness
of optical inspection tools that utilize fluorescence to discriminate
between the metallic and prepreg regions of printed circuit boards.

      A recent improvement in optical inspection capability is the
development of tools that utilize fluorescence to distinguish between
copper circuitry and the prepreg substrate.  These tools generally
function by scanning the surface of the printed circuit board with a
He-Cd laser beam emitting in the blue to near-UV while simultaneously
monitoring the fluorescence of the excited area. Discrimination
between metal and the prepreg is possible since the prepreg is weakly
fluorescent while the metal is totally non-fluorescent.  A method to
further improve the capabilities of such tools is to spike the
prepreg resins with a small quantity (typically 1-100 ppm) of a
highly fluorescent material that absorbs at the He-Cd laser emission
lines.  This results in an increased prepreg-to-metal fluorescence
signal ratio.

      A variety of fluorescent compounds are suitable for this
purpose, including, but not limited to, fluorescein, rhodamine,
eosin, coumarins, carbocyanines and styryls.