Electrostatic discharge detector

• US 5,461,369 A
• Filed: 06/24/1994
• Issued: 10/24/1995
• Est. Priority Date: 08/13/1990
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Campbell, Jeffrey D., Gearing, Graham O.
• Primary Examiner(s): Hofsass, Jeffery A.
• Application Number:
  US08/265,001
• Time in Patent Office: 487 Days
• Field of Search: 340/657, 340/649, 340/660, 340/661, 340/650, 340/651, 361/212, 324/457
• US Class Current: 340/649
• CPC Class Codes: G01R 29/12 Measuring electrostatic fields or voltage-potential

Abstract

A detector for detecting electrostatic discharge events in an electronic component, assembly or system and including a display element which produces an immediate indication on exposure to a change in voltage level, an electrostatic discharge sensor, and circuit means for connecting said sensor to said display element. In one embodiment, the detector and the board or other device to be monitored are mounted in a housing having a visual access window with the display element of the detector viewable through the access window and with the detector positioned at the electronic device being monitored.

Claims

1. In a detector for detecting and indicating prior occurrence of an electrostatic discharge event of any polarity in an electronic component or assembly device having electrical terminals, the combination of:

a non-destructive direct reading display element which switches indication from a first state to a second state on exposure to a change in voltage level;

an electrostatic discharge sensor for sensing electrostatic discharge events of either polarity resulting from build-up of an electrostatic potential and a discharge of said electrostatic potential;

circuit means for connecting said sensor to said display element to switch said indicator from said first state to said second state; and

means for maintaining display said element in said second state thereby subsequently indicating the earlier occurrence of an electrostatic discharge event.

2. A detector as defined in claim 1 wherein said display element is a liquid crystal display.

3. A detector as defined in claim 2 wherein said display element is a ferroelectric liquid crystal display.

4. A detector as defined in claim 2 including means for mounting said sensor and display element directly on the device to be monitored.

5. A detector as defined in claim 4 wherein said means for mounting includes a housing for said display element and sensor with clip means for attaching said housing to the device to be monitored.

6. A detector as defined in claim 2 wherein said sensor includes magnetic coupling means between the device to be monitored and said display element.

7. A detector as defined in claim 6 wherein said magnetic coupling means includes a closed conductor loop for positioning at the device to be protected and connected to said display element.

8. A detector as defined in claim 7 including means for mounting said conductor loop and display element directly on the device to be monitored.

9. A detector as defined in claim 8 wherein said means for mounting includes a base with said display element on one side and an adhesive layer on the opposite side.

10. A detector as defined in claim 6 wherein said magnetic coupling means includes a plurality of conductors at different orientations, and a bridge rectifier circuit for connecting said conductors to said display element.

11. A detector as defined in claim 4 wherein said means for mounting includes a base with said display element on one side and an adhesive layer on the opposite side.

12. A detector as defined in claim 1 wherein said sensor includes amplifier means, and

means for connecting an output of said amplifier means to said display element.

13. A detector as defined in claim 12 including means for mounting said sensor and display element directly onto the device to be monitored.

14. A detector as defined in claim 13 wherein the device to be monitored is a human assembler providing a ground connection for said display element, with said sensor and display element in a package, and including means for attaching said package to said assembler.

15. A detector as defined in claim 12 including reset means for resetting said display element to its original state after said change of indication.

16. A detector as defined in claim 12 wherein said display element is a liquid crystal display.

17. A detector as defined in claim 12 wherein said display element is a ferroelectric liquid crystal display.

18. A detector as defined in claim 12 wherein said display element is a twisted nematic-element.

19. A detector as defined in claim 12 wherein said display element is a smectic A element.

20. A detector as defined in claim 12 including means for mounting said sensor and display element on the device to be monitored and having a housing for said display element and sensor with clip means for attaching said housing to the device to be monitored.

21. A detector as defined in claim 12 wherein said sensor includes magentic coupling means between the device to be monitored and said display element.

22. A detector as defined in claim 21 wherein said magnetic coupling means includes a closed conductor loop for positioning at the device to be protected and connected to said display element.

23. A detector as defined in claim 22 including means for mounting said conductor loop and display element directly on the device to be monitored.

24. A detector as defined in claim 23 wherein said means for mounting includes a base with said display element on one side and an adhesive layer on the opposite side.

26. A detector as defined in claim 12 wherein said means for mounting includes a base with said display element on one side and an adhesive layer on the opposite side.

27. A detector as defined in claim 12 wherein said sensor includes antenna means, and

means for connecting said antenna means to an input of said amplifier means and connecting an output of said amplifier means and the ground of the device to be monitored to said display element.

28. A detector as defined in claim 27 including means for mounting said sensor and display element directly onto the device to be monitored.

29. A detector as defined in claim 27 wherein said antenna means includes first and second antennae, and circuit means for connecting said first antenna and second antenna into said amplifier means for receiving ESD events of different polarity.

25. A detector as defined in claim 25 wherein said magnetic coupling means includes a plurality of conductors at different orientations, and a bridge rectifier circuit for connecting said conductors to said display element.

30. In a detector for detecting and indicating prior occurrence of an electrostatic discharge event of any polarity in an electronic component or assembly device, the combination of:

a housing having a visual access window;

a detector carrier having a display element which switches indication from a first state to a second state on exposure to a change in voltage level,

an electrostatic discharge sensor for sensing electrostatic discharge events of either polarity resulting from build-up of an electrostatic potential and a discharge of said electrostatic potential,

circuit means for connecting said sensor to said display element to switch said indicator from said first state to said second state, and

means for maintaining said display element in said second state thereby subsequently indicating the earlier occurrence of an electrostatic discharge event; and

an electronic device to be monitored;

said housing including means for mounting said detector carrier and electronic device therein, with said display element viewable through said access window and with said carrier positioned at said device.