Electro-luminescent method and testing system for unpopulated printed circuit boards, ceramic substrates, and the like having both electrical and electro-optical read-out
First Claim
1. An improved testing system employing gaseous discharge within a sealable substantially gastight chamber for the electrical testing of items such as printed circuit boards, and ceramic substrates and for continuity and other electrical conductivity characteristics, said chamber having a readily opened and closed access opening for placement of items under test therein, means for introducing a gaseous atmosphere capable of electro-luminescence at low pressures into the sealable chamber with an item to be tested in place, movable probe means disposed within the sealable chamber for coupling one terminal of a variably controlled constant current source of electric potential to desired test points located on the surface of an item under test, a grid-like array of conductive wires lying in the same plane within the sealable chamber and spaced-apart from the item under test, means for coupling a remaining opposite polarity potential terminal of said constant current source of electric potential to the grid-like array of conductive wires whereby electro-luminescent plasma is produced in the gaseous atmosphere within the sealable chamber around test points contacted by said probe means and around all conductive points on the item under test having electrical continuity therewith which are exposed to the gaseous atmosphere, and measuring means for measuring the voltage drop produced across the electro-luminescent plasma for respective settings of the movable probe for comparison to a standard and use as a measure of the continuity and other electrical conductivity characteristics of the item under test.
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Accused Products
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.
64 Citations
34 Claims
- 1. An improved testing system employing gaseous discharge within a sealable substantially gastight chamber for the electrical testing of items such as printed circuit boards, and ceramic substrates and for continuity and other electrical conductivity characteristics, said chamber having a readily opened and closed access opening for placement of items under test therein, means for introducing a gaseous atmosphere capable of electro-luminescence at low pressures into the sealable chamber with an item to be tested in place, movable probe means disposed within the sealable chamber for coupling one terminal of a variably controlled constant current source of electric potential to desired test points located on the surface of an item under test, a grid-like array of conductive wires lying in the same plane within the sealable chamber and spaced-apart from the item under test, means for coupling a remaining opposite polarity potential terminal of said constant current source of electric potential to the grid-like array of conductive wires whereby electro-luminescent plasma is produced in the gaseous atmosphere within the sealable chamber around test points contacted by said probe means and around all conductive points on the item under test having electrical continuity therewith which are exposed to the gaseous atmosphere, and measuring means for measuring the voltage drop produced across the electro-luminescent plasma for respective settings of the movable probe for comparison to a standard and use as a measure of the continuity and other electrical conductivity characteristics of the item under test.
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14. An improved testing system employing gaseous discharge within a sealable substantially gastight chamber for electrical testing of items such as printed circuit boards, and ceramic substrates for continuity and other electrical conductivity characteristics;
- said chamber having a readily opened and closed access opening for placement of items under test therein;
automatically controlled means for purging and introducing a gaseous atmosphere capable of electro-luminescence at low pressures into the sealable chamber with an item to be tested in place;
automatically controlled movable probe means disposed within the sealable chamber for coupling one terminal of a variably controlled constant current source of electric potential to desired test points located on a surface of an item under test;
a grid-like array of conductive wires lying in the same plane within the sealable chamber and spaced-apart from the item under test;
automatically controlled means for coupling a remaining opposite polarity potential terminal of said constant current source of electric potential to the grid-like array of conductive wires whereby electro-luminescent plasma is produced in the gaseous atmosphere within the sealable chamber around test points contacted by said movable probe means and around all conductive points on the item under test having electrical continuity therewith which are exposed to the gaseous atmosphere;
measuring means for measuring the differences in voltage drop produced across the electroluminescent plasma for respective settings of the movable probe;
a central control computer having a display;
said control computer being responsive to the opening and closing of the access opening for automatically controlling a means for purging and refilling the gastight chamber with ionizable gas;
said control computer also being responsive to the position of the movable probe means and automatically controlling its repositioning at selected new settings in accordance with a predetermined schedule;
said control computer further serving automatically to control the timing of application and current value of the constant current source of potential to the array of conductive wires, and said control computer being further responsive to the measuring means for automatically deriving an indication of the electro-luminescent plasma resistance at each movable probe setting pursuant to the relation Plasma Resistance=Voltage/Current and for comparison of the derived Plasma Resistance value to a standard value for the particular setting of the movable probe for further deriving an automatic output indication of the conductivity characteristics of the item under test at that setting. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
- said chamber having a readily opened and closed access opening for placement of items under test therein;
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22. A method of testing conductivity characteristics of ceramic substrates, and printed circuit boards which have electrically conductive interconnected parts, pads, pathways, vias and their conductive surfaces for the existence of discontinuities (breaks), undesired conductive areas (shorts) or other irregularities in size or shape using a testing system employing an electro-luminescent plasma produced in a gaseous atmosphere contained within a sealable, substantially gastight test chamber within which an item under test is supported;
- the testing system further including a grid-like array of parallel conductor wires lying in substantially the same plane and arrayed within the sealable chamber over an item under test and spaced apart therefrom, and movable probe means for contacting selected test points on an item under test to produce an excitation electric field across the gaseous atmosphere and induce the formation of electro-luminescent plasma therein;
said method comprising;introducing an item to be tested into the interior of the test chamber and sealing it closed in a substantially gastight manner; introducing a gaseous atmosphere capable of electro-luminescence at low pressure into the interior of the test chamber along with the item under test; coupling one terminal of a constant current source of excitation electric potential with the movable probe means to selected test points located within an x-y plane on the surface of a item under test; coupling an opposite polarity potential terminal of the variably controlled constant current source of electric potential to the grid-like array of parallel conductor wires whereby electro-luminescent plasma is produced within the chamber around the test points contacted by the movable probe means and around all conductive points on the item under test having electrical continuity therewith which are exposed to the gaseous atmosphere; and measuring differences in voltage drop produced across the electro-luminescent plasma for respective settings of the movable probe means for comparison to a standard and use as a measure of the continuity and other electrical conductivity characteristics of the item under test. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
- the testing system further including a grid-like array of parallel conductor wires lying in substantially the same plane and arrayed within the sealable chamber over an item under test and spaced apart therefrom, and movable probe means for contacting selected test points on an item under test to produce an excitation electric field across the gaseous atmosphere and induce the formation of electro-luminescent plasma therein;
Specification