Voltage injector and detector for printed circuit board testing

• US 20070024272A1
• Filed: 07/28/2005
• Published: 02/01/2007
• Est. Priority Date: 07/28/2005
• Status: Active Grant

• Current Assignee: Varex Imaging Corporation
• Original Assignee: Varian Medical Systems Incorporated (Siemens AG)
• Inventors: Zentai, George
• Granted Patent: US 7,355,385 B2
• Time in Patent Office: Days
• US Class Current: 324/763.10
• CPC Class Codes: G01R 31/2812 Checking for open circuits or shorts, e.g. solder bridges; Testing conductivity, resistivity or impedance of connections G01R31/66

Abstract

One embodiment includes an injector pixel array having injector pixels each coupled to the bottom surface of a conductive material having a directional electrical conductivity only in a direction corresponding to a path between the bottom surface and top surface of the conductive material. Each injector pixel includes a semiconductor based switch coupled to a charge or voltage driver to inject a charge or voltage into each injector pixel. Embodiments, also include a detector pixel array having detector pixels each coupled to the bottom surface of the directionally conductive material. Each detector pixel includes a semiconductor based switch coupled to a charge or voltage storage capacitor to detect a charge or voltage at each detector pixel.

Claims

1. An apparatus, comprising:

a conductive material having a first surface and a second surface, the conductive material having a directional electrical conductivity only in a direction corresponding to a path in a direction from the second surface to the first surface, and only in a direction corresponding to a path in a direction from the first surface to the second surface;

an injector pixel array having a plurality of injector pixels, each injector pixel coupled to the second surface of the conductive material and having a semiconductor based switch coupled to a driver to inject a charge or a voltage into each injector pixel.

2. The apparatus of claim 1, wherein the driver is one of a charge injector, a voltage injector, a pulse addresser, and an excitation pulse generator.

3. The apparatus of claim 1, wherein each injector pixel comprises a thin film transistor (TFT) or a complementary metal oxide semiconductor (CMOS) switch coupled between an injector electrode and a TFT or a CMOS driver amplifier.

4. The apparatus of claim 1, further comprising:

a detector pixel array having a plurality of detector pixels, each detector pixel coupled to the second surface of the conductive material and having a thin film transistor (TFT) or a complementary metal oxide semiconductor (CMOS) detector capacitor coupled to a TFT or CMOS switch coupled to detect a charge or a voltage at each detector pixel.

5. The apparatus of claim 4, wherein an electrostatic charge corresponding to a voltage injected by a driver through a trace on a printed circuit board (PCB) and electrically coupled to the first surface may be detected from the trace by a detector pixel.

6. The apparatus of claim 4, wherein the injector pixels are the same as the detector pixels and the apparatus is an electrostatic imager to test traces of a PCB by injecting charges or voltages into the traces using the injector pixels and detecting the injected charges or voltages using the detector pixels.

7. The apparatus according to claim 6, further comprising:

a tri-state enable driver circuit at each pixel to disconnect the driver from the pixel during detection.

9. The apparatus of claim 4, wherein an electrostatic charge or a voltage injected by a driver through a first trace on a first side of a printed circuit board (PCB) and electrically coupled to the first surface may be detected by a detector pixel from a second trace on a second side of the PCB coupled to the first trace by at least one conductive via through the PCB.

10. The apparatus of claim 4, wherein the apparatus is a first apparatus, the first surface is electrically coupled to a first trace on a first side of a printed circuit board (PCB) having a conductive via connecting the metal trace to a second trace on a second side of the PCB, and

further comprising a second apparatus similar to the first apparatus, having a first surface electrically coupled to the second trace to detect a signal injected by the first apparatus.

11. The apparatus of claim 4, wherein the injector pixel array is part of a first device coupled to a controller and the detector pixel array is a part of a different second device coupled to the controller.

12. The apparatus of claim 4, further comprising:

a controller to apply a plurality of test voltages to a plurality of conductive traces of a PCB using a plurality of drivers, and to check a readout pattern from a plurality of detector pixels at a plurality of locations associated with the conductive traces, wherein the readout pattern comprises a plurality of readout voltages corresponding to the plurality of applied voltages.

13. The apparatus of claim 1, wherein the conductive material is configured to conduct electricity only in directions corresponding to a path between a contact point on the second surface and a contact point on the first surface.

14. The apparatus of claim 1, wherein the conductive material comprises:

a layer of electrically insulating material having a plurality of disconnected conductive fibers extending from the second surface to the first surface.

15. The apparatus of claim 14, wherein the insulating material is one of silicon and a hardened epoxy, other soft insulating material and the conductive fibers are carbon fibers, metal ferromagnetic fibers, or semiconductor fibers.

16. The apparatus of claim 14, wherein the conductive fibers are electrically coupled to a trace of a PCB disposed over the injector pixel.

17. The apparatus of claim 1, wherein the conductive material comprises:

a thickness between 10 E-6 meters and 2000 E-6 meters in thickness.

8. The detector of 6, further comprising:

a switch to switch between connecting and disconnecting the driver from the pixel.

18. A method comprising:

injecting a voltage into a conductive trace of a printed circuit board (PCB) from a voltage injector of a flat panel injection pixel array, the conductive trace being electrically coupled to a first surface of a conductive material having a second surface, the conductive material comprising a directional electrical conductivity only in directions substantially perpendicular to one of the second surface and the first surface; and

detecting the injected voltage from the conductive trace using an electrostatic voltage detector of a flat panel imaging pixel array.

19. The method of claim 18, wherein injecting a voltage comprises applying a voltage to the conductive material, and detecting the injected charge comprises measuring a capacitive charge based on the voltage on a detector capacitor.

20. The method of claim 18, further comprising:

injecting a plurality of voltages into at least one conductive trace from a plurality of injectors;

detecting the injected voltages from the at least one conductive trace using at least one detector pixel; and

producing an image of the at least one conductive trace based on the detected injected voltages.

21. The method of claim 20, further comprising:

identifying defects in the at least one trace according to the image.