Methods and systems employing infrared thermography for defect detection and analysis

• US 20030137318A1
• Filed: 01/22/2003
• Published: 07/24/2003
• Est. Priority Date: 01/23/2002
• Status: Active Grant

• Current Assignee: Marena Systems Corporation
• Original Assignee: Marena Systems Corporation
• Inventors: Belikov, Sergey, Enachescu, Marian
• Granted Patent: US 6,840,666 B2
• Time in Patent Office: Days
• US Class Current: 324/770
• CPC Class Codes: G01R 31/308 using non-ionising electromagnetic radiation, e.g. optical radiation investigating or analysing materials by the use of optical means G01N21/00; image analysis G06T7/00

Abstract

Described are methods and systems for providing improved defect detection and analysis using infrared thermography. Test vectors heat features of a device under test to produce thermal characteristics useful in identifying defects. The test vectors are timed to enhance the thermal contrast between defects and the surrounding features, enabling IR imaging equipment to acquire improved thermographic images. In some embodiments, a combination of AC and DC test vectors maximize power transfer to expedite heating, and therefore testing. Mathematical transformations applied to the improved images further enhance defect detection and analysis. Some defects produce image artifacts, or “defect artifacts,” that obscure the defects, rendering difficult the task of defect location. Some embodiments employ defect-location algorithms that analyze defect artifacts to precisely locate corresponding defects.

Claims

1. A test configuration comprising:

a. a display panel including;

i. a plurality of source lines;

ii. a plurality of control lines;

iii. a plurality of common lines;

iv. a two-dimensional array of display elements, each display element including a transistor and a capacitor, wherein the transistor has a first current-handling terminal connected to one of the source lines, a second current-handling terminal, and a control terminal connected to one of the control lines, and wherein the capacitor has a first capacitor terminal connected to the second current-handling terminal and a second capacitor terminal connected to one of the common lines;

b. an infrared detector positioned to receive infrared radiation from the display panel; and

c. a signal generator having;

i. a first test-signal output terminal connected to at least one of the source lines;

ii. a second test-signal output terminal connected to at least one of the control lines; and

iii. a third test-signal output terminal connected to at least one of the common lines.

2. The test configuration of claim 1, wherein the signal generator simultaneously provides a first test vector on the first test vector output terminal, a second test vector on the second test-signal output terminal, and a third test vector on the third test-signal output terminal.

3. The test configuration of claim 2, wherein at least one of the first and third test vectors is an AC signal.

4. The test configuration of claim 3, wherein the second test vector is a DC signal biasing on the transistor.

5. The test configuration of claim 2, wherein the second test vector turns the transistor on.

6. The test configuration of claim 2, wherein at least one of the first and third test vectors is of a test frequency and encounters a resistance and a capacitance, and wherein the test frequency is matched to the capacitance and the resistance to provide maximum power transfer from the signal generator to the panel.

7. The test configuration of claim 1, wherein the signal generator applies a test vector across the source and common lines to develop a test current through the first and second current-handling terminals of the transistor.

8. A test configuration comprising:

a. an electrical circuit having at least one defect disposed within a defect region, the defect region having an initial temperature;

b. an infrared detector positioned to receive infrared radiation from the defect region; and

c. a signal generator having at least one test-signal output terminal connected to the electrical circuit, the signal generator applying a test vector to the defect via the electrical circuit, wherein the defect exhibits a thermal response to the applied test vector;

d. wherein the infrared detector captures an image of the defect after application of the test vector and before the defect reaches 95% of a difference between the initial temperature and a final equilibrium temperature.

9. The test configuration of claim 8, wherein the infrared detector captures the image before the defect reaches about 86.5% of the difference.

10. The test configuration of claim 8, wherein the infrared detector captures the image before the defect reaches about 63.5% of the difference.

11. The test configuration of claim 8, wherein the signal generator includes a second test-signal output terminal, the electrical circuit comprising a transistor having a first current-handling terminal connected to the first-mentioned test-signal output terminal, a control terminal connected to the second test-signal output terminal, and a second current-handling terminal.

12. The test configuration of claim 11, wherein the test vector is an AC signal.

13. The test configuration of claim 12, wherein the signal generator applies a second test vector to the control terminal via the second test-signal output terminal.

14. The test configuration of claim 13, wherein the second test vector turns the transistor on.

15. The test configuration of claim 11, wherein the signal generator includes a third test-signal output terminal, the test configuration further comprising a capacitance connected between the second current-handling terminal of the transistor and the third test-signal output terminal.

16. A method for identifying a defect on an electrical circuit, the method comprising:

a. applying test vectors, at a first instant, to the defect via the electrical circuit, wherein the defect exhibits a thermal response to the test vectors, the thermal response being characterized by a thermal time constant; and

b. capturing a test image of the defect at a second instant separated from the first instant by less than three time constants.

17. The method of claim 16, wherein the second instant is separated from the first instant by less than two time constants.

18. The method of claim 16, wherein the second instant is separated from the first instant by less than one time constant.

19. The method of claim 16, further comprising repeating steps (a) and (b) at least twice to capture a plurality of test images.

20. The method of claim 19, further comprising capturing a reference image between ones of the plurality of test images.

21. An automated method of locating at least one defect on an object of interest, wherein the object includes at least one defect region corresponding to the defect and a defect-free region absent the defect, the method comprising:

a. acquiring an image of the object, the image including image data spatially correlated to the object, the image data including;

i. defect data spatially correlated to the defect region; and

ii. defect-artifact data spatially correlated to portions of the defect-free region; and

b. analyzing the defect-artifact data.

22. The method of claim 21, further comprising classifying the defect-artifact data as a member of one of a plurality of artifact types.

23. The method of claim 22, wherein the artifact types include at least one of point-type, line-type, and corner-type.

24. The method of claim 21, further comprising filtering the image data to remove at least one type of defect, thereby creating a type-specific image.

25. The method of claim 21, further comprising:

a. applying a first threshold value to the image data to create a first thresholded image, the first thresholded image depicting a first defect area in the defect region and a first defect-artifact area encompassing the first defect area and extending into the defect-free region; and

b. applying a second threshold value to the image data to create a second thresholded image, the second thresholded image depicting a second defect area in the defect region and a second defect-artifact area encompassing the second defect area and extending into the defect-free region.

26. The method of claim 25, further comprising selecting a first peak within the first defect-artifact area, selecting a second peak within the second defect-artifact area, and calculating a gradient extending between the first and second peaks.

27. The method of claim 26, further comprising calculating the defect coordinates using the gradient.

28. The method of claim 25, wherein the first and second defect areas correspond spatially to the defect region.

29. An imaging systems for localizing a defect on an object under test, the imaging system comprising:

a. a excitation source applying a test vector to the defect, wherein the defect exhibits a response to the applied test vector;

b. an image detector positioned to observe the response of the defect, thereby producing an image including defect data and defect-artifact data encompassing the defect data; and

c. an image processor analyzing the defect-artifact data and the defect data to locate the defect data within the defect-artifact data.

30. The imaging system of claim 29, wherein the response is a thermal response.

31. The imaging system of claim 29, wherein analyzing the defect-artifact data comprises:

a. applying a plurality of threshold values to the image to produce a plurality of thresholded images;

b. wherein a number of the thresholded images include respective defect artifacts corresponding to the defect region.

32. The imaging system of claim 31, further comprising a type-specific filter sorting the defect artifacts in each thresholded image by type to produce type-specific images having type-specific defect artifacts.

33. The imaging system of claim 32, wherein the image processor includes a data structure associating type-specific defect artifacts from different type-specific images.

34. The imaging system of claim 33, wherein the image processor establishes a gradient between peak values of the type-specific defect artifacts.

35. The imaging system of claim 34, wherein the image processor calculates the location of the defect using the gradient.

36. An inspection system comprising:

a. an object under test, including at least one defect;

b. a means for heating the defect and related resources;

c. an infrared imaging device capturing a thermal image heated object, the thermal image including defect data representative of the defect and defect-artifact data representative of the related resources; and

d. image-processing means for locating the defect data within the defect-artifact data.