Apparatus and method using photoelectric effect for testing electrical traces

• US 6,369,591 B1
• Filed: 12/15/1999
• Issued: 04/09/2002
• Est. Priority Date: 01/14/1999
• Status: Expired due to Fees

• Current Assignee: Mannatech Incorporated
• Original Assignee: Mannatech Incorporated
• Inventors: Miles, George E. III, Cugini, Mario A., Brakley, Jeff, Ravich, Gilbert Norman, Giusti, Ralph Lynn
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): LEROUX, ETIENNE PIERRE
• Application Number:
  US09/461,801
• Time in Patent Office: 846 Days
• Field of Search: 324/752, 324/158.R, 250/492.2, 250/310, 156/345, 356/369, 438/8
• US Class Current: 324/750.14
• CPC Class Codes: G01R 31/309 of printed or hybrid circuits or circuit substrates

Abstract

A tester for electrical traces such as on a circuit board generally comprises an electromagnetic beam source such as a laser producing an ultraviolet beam, a vacuum chamber, an electrode circuit including electrodes and corresponding electronics including ammeters for measuring photoelectron flow between traces and electrodes, a controller, laser beam optics, an image acquisition system, and a pair of broadband UV lights. The board containing traces under test is disposed in the vacuum chamber at lowered pressure with grid electrodes lying close to the trace area on each side of the board. Electrode electronics selectively maintain a known potential on each electrode. The exact location of traces are determined by an image acquisition system. The board and traces are initialized to a known voltage. Photoelectric effect using ultraviolet laser beams is used to determine continuity between two points on a trace and shorts between traces.

Claims

1. A tester for testing an electrical trace on a board capable of test without physically contacting the electrical trace comprising:

a board having a first planar side and an opposing second planar side and an electrical trace formed on at least one planar side, said electrical trace having electrical continuity with both said first planar side and said second planar side;

an electromagnetic source to direct a first beam of electromagnetic radiation on said first planar side to contact said electrical trace thereby producing a photoelectric effect thereon and to direct a second beam of electromagnetic radiation on said second planar side to contact said electrical trace thereby producing a photoelectric effect thereon;

an electrode circuit including a first grid electrode disposed near said first planar side and a second grid electrode disposed near said second planar side;

said electrode circuit for maintaining said electrode as a given potential for collecting electrons liberated by the photoelectric effect of the beams on the electrical trace;

a meter for measuring photoelectric current between said electrode circuit and the electrical trace.

2. The tester of claim 1, further including broadband electromagnetic source for simultaneously irradiating a plurality of electrical traces, said first grid electrode, and said second grid electrode with electromagnetic radiation for producing a photoelectric effect thereon.

3. The tester of claim 1 wherein said first grid electrode is substantially transparent to said beam.

4. The tester of claim 3 wherein said first grid electrode is a sheet electrode transparent to the beam including a surface facing the electrical trace having a thin conductive film thereon.

5. The tester of claim 1 further including:

a vacuum chamber for containing said electrical trace.

6. A tester for testing for shorts between a first electrical trace and a second electrical trace on a board capable of test without physically contacting the electrical trace comprising:

a board having a first planar side with a first electrical trace and an opposing second planar side with a second electrical trace, wherein said first and second electrical traces are electrically interconnected;

electromagnetic source to direct a first beam of electromagnetic radiation on the first electrical trace thereby producing a photoelectric effect thereon and to direct a second beam of electromagnetic radiation on the second electrical trace thereby producing a photoelectric effect thereon;

an electrode circuit including a first grid electrode disposed near the first electrical trace for collecting electrons liberated by the photoelectric effect of the first beam on the first electrical trace and a second grid electrode disposed near the second electrical trace for collecting electrons liberated by the photoelectric effect of the second beam on the second electrical trace; and

a meter for measuring photoelectric current between said electrode circuit and the second electrical trace.

7. The tester of claim 6 further including broadband electromagnetic source for simultaneously irradiating a plurality of electrical traces, said first grid electrode, and said second grid electrode with electromagnetic radiation for producing a photoelectric effect thereon.

8. The tester of claim 6 wherein said first grid electrode is substantially transparent to said beam.

9. The tester of claim 8 wherein said first grid electrode is a sheet electrode transparent to the beam including a surface facing the electrical trace having a thin conductive film thereon.

10. A method of testing an electrical trace on a board capable of test without physically contacting the electrical trace comprising:

providing a board having a first planar side and an opposing second planar side and an electrical trace on at least one planar side, said electrical trace having electrical conductivity from both said first planar side and said second planar side;

disposing a first grid collector electrode of an electrode circuit near said first planar side for collecting electrons liberated by photoelectric effect on the electrical trace;

measuring photoelectric current between said first grid collector and said electrical trace;

disposing a second grid collector electrode of said electrode circuit near said second planar side for collecting electrons liberated by photoelectric effect on said second location on said electrical trace;

maintaining the first and second grid collector electrodes at a known potential; and

directing a first electromagnetic beam on said first planar side to contact said electrical trace thereby producing a photoelectric effect on the electrical trace until the electrical trace is charged to a known potential;

directing a second beam of electromagnetic radiation on said second planar side to contact said electrical trace thereby producing a photoelectric effect thereon; and

measuring photoelectric current between said electrical trace and said second grid collector electrode.

11. The method of claim 10 further including the step of:

disposing said board and said first and second grid collectors in a vacuum chamber before directing said first and second beams.

12. The method of claim 10 further including the step of:

initializing said at least one electrical trace to a known voltage before directing a first electromagnetic beam on said first planar side to contact said electrical trace.

13. The method of claim 12 wherein the step of initializing said at least one electrical trace includes:

irradiating said at least one electrical trace and said first grid collector electrode with a broadband electromagnetic source for producing a photoelectric effect thereon.

14. The method of claim 10 further including:

supplying a positive potential to said second grid collector electrode.

15. The method of claim 14 wherein the step of initializing said at least one electrical trace includes:

dithering an electromagnetic beam on said at least one electrical trace and said first grid collector electrode until said at least one electrical trace is charged to a known potential.

16. The method of claim 10 further including:

maintaining said second grid collector electrode at a known potential.

17. The method of claim 16 further including the step of:

initializing the trace to a known voltage before directing a first electromagnetic beam on a first location on a trace.