Combining multiple independent sources of information for classification of devices under test

• US 20050251370A1
• Filed: 05/10/2004
• Published: 11/10/2005
• Est. Priority Date: 05/10/2004
• Status: Active Grant

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Li, Jonathan Qiang, Usikov, Daniel A.
• Granted Patent: US 7,440,862 B2
• Time in Patent Office: Days
• US Class Current: 702/190
• CPC Class Codes: G01R 31/31707 Test strategies methods for generation of test sequences G01R31/318371
• CPC Class Codes: G01R 31/31835 Analysis of test coverage or failure detectability

Abstract

Embodiments of the present invention use the results of a plurality of defect detecting tests and adjust the result of each test in a manner that reflects the accuracy of the test that produced it. A manufactured unit can then be evaluated using a mathematical combination of the adjusted results.

Claims

1. A method for determining that a device under test is defective, said method comprising:

weighting the results of a plurality of defect detecting techniques, wherein said weighting is related to an accuracy of said technique; and

determining a probability that said unit has a defect, wherein said determination is made by combining said results from said plurality of techniques.

2. The method of claim 1 further comprising:

determining said accuracy of each said technique by comparing results for each said technique performed on a standard with expected results for said standard.

3. The method of claim 2 wherein said accuracy determination uses a Gaussian model.

4. The method of claim 1 further comprising:

calculating a likelihood for each said technique by mathematically combining said results for said technique and said accuracy for said technique.

5. The method of claim 4 further comprising:

calculating a probability that said unit has a defect by mathematically combining said likelihoods.

6. The method of claim 5 wherein said likelihoods are converted to probabilities and are combined using a Bayesian Voting Formula.

7. A system for evaluating a unit, said system comprising:

a plurality of testing techniques, wherein each said technique detects the presence of at least one characteristic, and wherein an accuracy of each said technique is capable of being determined; and

means for analyzing results of said techniques that determines a probability that said at least one characteristic is detected by using a combination of each technique'"'"'s results and each said technique'"'"'s accuracy, wherein said probability is used to evaluate said unit.

8. The system of claim 7 further comprising:

at least one standard having a known characteristic profile, wherein said standard is used to determine said accuracy for each said technique.

9. The system of claim 7 wherein said at least one characteristic is a defect.

10. The system of claim 7 further comprising:

at least one standard having a least one known defect;

at least one standard which is substantially free of defects; and

wherein said accuracy of each said technique is determined by comparing results obtained by performing each said technique on each said standard with anticipated results for each said standard.

11. A computer readable storage medium storing computer executable code, said code comprising:

code to calculate a confidence factor for each of a plurality of tests;

code that combines results from each of said test with said confidence factor for that test to produce a likelihood for each said test; and

code that combines said likelihoods to arrive at a determination regarding a unit tested by each said test.

12. The code of claim 11 wherein said determination relates to whether said unit is defective.

13. The code of claim 11 further comprising:

code to change each said likelihood into a probability, and

code that combines said probabilities using a Bayesian Voting Formula.

14. The code of claim 11 further comprising:

code to compare results that each said test produces for a standard with results that are anticipated for said standard, wherein said comparison is used in said calculation of said confidence factors.

15. The code of claim 11 wherein said determination produces at least one graph of receiver operating characteristics.

16. A method of evaluating a unit, said method comprising:

providing a plurality of testing techniques for detecting defects in said unit;

testing at least one standard using each said technique, wherein said standard has a known defect profile;

calculating a weighting factor for each said technique from results of said standard testing; and

testing said unit using each said technique, wherein an acceptability of said unit is determined from a combination of said unit testing results, and said weighting factors.

17. The method of claim 16 further comprising:

producing a first feature set by testing a standard having at least one known defect;

producing a second feature set by testing a standard which is substantially free of defects;

generating a statistical measurement of accuracy for each said technique from said first and second feature sets.

18. The method of claim 17 wherein said generating uses a Gaussian model.

19. The method of claim 16 wherein at least one said techniques is an optical technique for the detection of defects on printed circuit boards.

20. The method of claim 16 wherein at least one said technique is an electrical conductivity technique.