Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
2000-03-30
2001-11-27
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C702S059000
Reexamination Certificate
active
06323653
ABSTRACT:
REFERENCE TO MICROFICHE APPENDICES
Appendices A, B, and C, which constitute parts of this disclosure, are microfiche appendices consisting of three sheets of microfiche having a total of 66 frames.
FIELD OF USE
This invention relates to techniques for detecting short circuit defects in plate structures such as a baseplate structure of a flat-panel cathode-ray tube (“CRT”) display.
BACKGROUND
A flat-panel display is a matrix-addressed flat-panel device typically formed with a baseplate structure and a faceplate structure situated opposite the baseplate structure. In a flat-panel CRT display of the gated field-emission type (“field-emission display”), the baseplate structure contains a generally flat baseplate, a lower level of generally parallel emitter electrodes extending over the interior surface of the baseplate, a dielectric layer overlying the emitter electrodes, and an upper level of control (or gate) electrodes extending over the dielectric layer generally perpendicular to the emitter electrodes. Electron-emissive elements are situated in cavities in the dielectric layer and are exposed through openings in the control electrodes.
During operation of the field-emission display (“FED”), electrons emitted from selected electron-emissive elements move towards the faceplate structure. The electrons strike corresponding light-emissive regions in the faceplate structure and cause them to emit light that produces an image on the exterior surface of a transparent faceplate. Each of the locations at which one of the control electrodes crosses one of the emitter electrodes in the baseplate structure defines a picture element (“pixel”) in a black and white display and a sub-pixel in a color display, three sub-pixels normally forming a color pixel.
Various types of defects can arise during flat-panel display fabrication. In a display having a plate structure that contains multiple levels of electrodes such as the baseplate structure of an FED, short circuits are of particular concern. A short circuit defect arises when an electrode in one level is unintentionally connected to an electrode in another level. For example, a short circuit defect can occur in an FED when an electrically conductive path extends through the inter-electrode dielectric layer to connect a control electrode to an emitter electrode.
Detection of short circuit defects is an important part of flat-panel display manufacture. In some instances, a short circuit defect can be corrected before the plate structures are connected together, thereby transforming a potentially defective display into a fully operative one. In other instances, a short circuit defect can be cut out of the display. While part of all of a pixel or sub-pixel is lost, the performance of the remainder of the display is often not affected significantly. The display is typically acceptable for certain applications.
Each location at which a control electrode crosses an emitter electrode in an FED could be tested for a short circuit defect by observing what happens when a suitable voltage is applied between the two electrodes while the remainder of the electrodes in the upper and lower levels are suitably grounded. Unfortunately, this type of short circuit testing procedure is extremely time-consuming for an PED with a large number of pixels.
Henley, U.S. Pat. No. 5,073,754, describes how a matrix-addressed liquid-crystal display (“LCD”) is tested for short circuit defects using a magnetic sensor of undisclosed configuration. The magnitude of current flowing through a short circuit defect increases with the magnitude of the sensed magnetic field. Henley scans the magnetic sensor across the periphery of the LCD and then examines the magnitudes of the sensed magnetic field to detect any short circuit defects between electrical conductors in one level and crossing electrical conductors in another level. As a result, currents that characterize short circuit defects can be identified rapidly.
When magnetic fields of relatively comparable strength are detected on multiple conductors at each level, Henley has trouble determining which of the conductor-crossing locations have short circuit defects and which do not. Instead, Henley simply classifies all of the concerned conductor-crossing locations as having short circuit defects even though short circuit defects normally do not exist at some of these locations. It is desirable to have a magnetic-sensing-based technique that more accurately determines the location of short circuit defects in plate structures, especially baseplate structures of matrix-addressed flat-panel CRT displays.
GENERAL DISCLOSURE OF THE INVENTION
The present invention furnishes techniques for processing magnetically obtained current data to accurately detect current-related defects such as short circuit defects. The techniques of the invention are typically employed in testing matrix-addressed plate structures for short circuit defects. Specifically, short circuit defects in baseplate structures of flat-panel CRT displays can be rapidly and accurately located in the invention.
In one aspect of the invention, a probability-based technique is utilized to detect short circuit defects in a plate structure having a group of first electrical conductors and a group of second electrical conductors that cross the first conductors. The second conductors are nominally electrically insulated from the first conductors. The expression “nominally electrically insulated” here means that the second conductors are substantially electrically insulated from the first conductors except for short circuit defects that variously electrically couple one or more of the second conductors to one or more of the first conductors.
Magnetic current sensing is performed on at least part of the first and second conductors to produce current data indicative of how much, if any, current flows through each of at least part of the conductors. A short circuit defect probability analysis is then applied to the current data for selecting a location where an identified one of the first conductors crosses an identified one of the second conductors as being most probable of having a short circuit defect. The sensed current carried by the identified first conductor is normally greater in value than the sensed current carried by any of the other first conductors. Also, the sensed current carried by the identified first conductor is normally closer in value to the sensed current carried by the identified second conductor than the sensed current flowing through any other second conductor.
The selected electrode-crossing location can be optically examined to determine whether it has the physical characteristics of a short circuit defect. A repair operation can also be performed at the selected location to remove any short circuit defect present there.
Assuming the presence of a short circuit defect at the selected electrode-crossing location, the plate structure can be checked for additional short circuit defects by first modifying the current data to subtract current of a selected short circuit value from the values of the sensed currents carried by the two conductors that define the selected location. The modified current data is then examined to determine whether current of value sufficient for at least one other short circuit defect seemingly flows through at least one first conductor and through at least one second conductor. If so, a short circuit defect probability analysis is applied to the modified current data for selecting a further electrode-crossing location as now being most probable of having a short circuit defect. Optical inspection and/or repair effort can be performed at the further electrode-crossing location. This procedure can then be appropriately repeated to find any further short circuit defects.
Detecting short circuit defects in the preceding manner is very efficient. To the extent that an electrode-crossing location does not actually have a short circuit defect even though that location is found during a stage of the probability analysis to be most probabl
Field John E.
Oberg Stephanie J.
Candescent Technologies Corporation
Karlsen Ernest
Kobert Russell M.
Meetin Ronald J.
Skjerven Morrill & MacPherson LLP
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