Electro-luminescent method and testing system for unpopulated printed

Abstract

A method and system for the electrical and electro-optical inspection and testing of unpopulated electronic printed circuit boards, ceramic substrates and other like items which have conductive pathways formed thereon, vias, through-connectors and other interconnected conducting surfaces. The item under test is placed within a sealable gastight chamber filled with an ionizable gaseous atmosphere, such as argon, at low pressure. An electro-luminescent gas plasma discharge is produced within the chamber between a grid placed either over or below the item under test by application of a positive polarity potential to the grid and selective application of a constant current negative potential to particular test points on the item to be tested via a computer controlled movable probe. In one embodiment of the invention, the resulting electro-luminescent gas plasma discharge resistance is measured and compared by a computer to a standard resistance value for the particular item under control at a particular setting of the movable probe as a measure of the conductivity characteristics of the item under test. Other embodiments of the invention, may also include computer controlled electro-optic scanning of the surfaces of the item under test by a scanning photometer detector. The output from the scanning photometer detector is supplied to a computer for comparison to a standard prestored in the computer from a previously tested good board or substrate. The two techniques may be combined in a single system which can inspect either one or both sides of a test circuit board or substrate.