Andrew J Lepage

US Patent:

49704613, Nov 13, 1990

Filed:

Jun 26, 1989

Appl. No.:

7/371589

Inventors:

Andrew J. LePage - Lowell MA

International Classification:

G01R 3100
G01R 3102

US Classification:

324158F

Abstract:

A circuit is tested for unwanted shorts and opens by positioning the circuit between a pair of electrodes in a chamber filled with an inert gas with the circuit conductors facing one of the electrodes. The circuit is charged by applying a selected voltage to the electrodes to produce an electric field extending generally perpendicular to the circuit, the voltage polarity being such that the one electrode carries the negative electrical charge. The circuit is then subjected to a pulsed laser beam brought to a focus between the one electrode and a selected spot on a conductor of the circuit so as to ionize the chamber gas at the beam focus to form a plasma so that an electric charge is imparted to that spot and to other circuit conductor portions having electrical continuity with that spot. The circuit is then discharged by reversing the polarity of the applied voltage and increasing the voltage magnitude substantially to the breakdown voltage of the chamber gas so as to form a glowing discharge plasma in the chamber gas opposite the charged portions of the circuit conductors. The circuit is observed to determine which portions of its conductors are glowing and therefore have electrical continuity with the selected conductor spot and which portions are not.

US Patent:

50327887, Jul 16, 1991

Filed:

Jun 26, 1989

Appl. No.:

7/371704

Inventors:

Diethelm G. Ringleb - Andover MA
Andrew J. LePage - Lowell MA

Assignee:

Digital Equipment Corp. - Maynard MA

International Classification:

G01R 3102

US Classification:

324158F

Abstract:

A test cell for non-contact testing a circuit board for shorts and opens includes a hermetically sealable container for that circuit board, at least one wall of the container providing access to permit a circuit board to be positioned at an imaging plane inside the container. A pair of planar electrodes positioned inside the container are spaced on opposite sides of and parallel to the imaging plane and these electrodes are connected to contacts on the exterior of the container so that the electrodes can be releasably connected to an external voltage source to provide an electric field inside the container which extends perpendicular to the imaging plane. One of these electrodes and the container wall adjacent thereto are transparent to light from a pulsed laser positioned outside the container which is arranged to image a selected spot on a conductor of a circuit positioned at the imaging plane. One or more valved gas fittings are mounted to the outside of the container so that the container can be releasably connected to external gas conduits to fill the container with an inert gas. Also a sensor may be provided inside the container to sense the gas pressure in the container.