Product defect detection using thermal ratio analysis
First Claim
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1. A method of detecting defects in a test sample of a product, comprising the steps of:
- generating a reference record for at least one reference sample of the product that does not have defects, comprising the sub-steps of;
(1) making an ambient-temperature thermal record of the reference sample at ambient temperature;
(2) making a plurality of elevated temperature thermal records of the reference sample at a plurality of respective elevated temperatures, including applying a respective thermal stimulus to the reference sample, and(3) making a first difference record for the reference sample from the ambient-temperature thermal records and one of the plurality of elevated temperature thermal records and at least a second difference record for the reference sample involving at least another of the plurality of elevated temperature thermal records,generating first and at least second difference records for the test sample by repeating sub-steps (1)-(3) with the test sample replacing the reference sample;
deriving at least one ratio record from the difference records for the reference sample and the test sample;
forming a composite record including at least the derived one ratio record; and
generating a defect indication when the composite record yields a statistical significant deviation from an expected value.
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Abstract
A method and apparatus for indicating defects in manufactured products employs, instead of the conventional thermal image subtraction, "thermal ratio analysis", which involves ratios of thermal data and their analysis including statistical analysis. Various techniques for "image" enhancement and for suppression of known artifacts are employed to facilitate the decision as to when a defect is detected. The thermal ratio analysis technique is particularly useful for detecting hidden defects in electronic circuitry, such as integrated circuits.
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Citations
40 Claims
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1. A method of detecting defects in a test sample of a product, comprising the steps of:
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generating a reference record for at least one reference sample of the product that does not have defects, comprising the sub-steps of; (1) making an ambient-temperature thermal record of the reference sample at ambient temperature; (2) making a plurality of elevated temperature thermal records of the reference sample at a plurality of respective elevated temperatures, including applying a respective thermal stimulus to the reference sample, and (3) making a first difference record for the reference sample from the ambient-temperature thermal records and one of the plurality of elevated temperature thermal records and at least a second difference record for the reference sample involving at least another of the plurality of elevated temperature thermal records, generating first and at least second difference records for the test sample by repeating sub-steps (1)-(3) with the test sample replacing the reference sample; deriving at least one ratio record from the difference records for the reference sample and the test sample; forming a composite record including at least the derived one ratio record; and generating a defect indication when the composite record yields a statistical significant deviation from an expected value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of detecting a defect in a test sample of a product, comprising the steps of:
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establishing a reference record for at least one reference sample of the product that does not have defects, comprising the sub-steps of; (1) making a base thermal record of the reference sample at a base value of a thermal stimulus; (2) making a plurality of changed value thermal records of the reference sample at a plurality of respective changed values of the thermal stimulus, including applying a respective changed-value thermal stimulus to the reference sample; and (3) making a first difference record for the reference sample from the base-value thermal record and one of the plurality of elevated value thermal records and a second difference record for the reference sample involving at least another of the plurality of elevated value thermal records; generating first and second difference records for the test sample by repeating sub-steps (1)-(3) with test sample replacing the reference sample; deriving at least one ratio record from the four difference records consisting of the first and second difference records for the reference sample and the first and second difference records for the test sample; generating a defect indication when the composite ratio record yields a statistically significant deviation from an expected value. - View Dependent Claims (10, 11, 12)
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13. A method of detecting a defect in a test sample of a product, comprising the steps of:
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establishing a reference record for at least one reference sample of the product that does not have defects, comprising the sub-steps of; (1) making an ambient-temperature thermal record of the reference sample at ambient temperature, (2) making a plurality of elevated temperature thermal records of the reference sample at a plurality of respective voltages applied to the sample to produce heating therein, including applying a respective voltage to the reference sample; (3) making a first difference record from the ambient-temperature thermal records and one of the plurality of elevated temperature thermal records and a second difference record involving at least another of the plurality of elevated temperature; generating a test record for the test sample by repeating sub-steps (1)-(3) with the test sample replacing the reference sample; (4) deriving at least one ratio record from the four difference records consisting of the first and second difference records for the test sample and the first and second difference records for the reference sample; forming a composite record including the at least one ratio record; and generating a defect indication when the composite record yields a statistically significant deviation from an expected value. - View Dependent Claims (14, 15, 16)
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17. A system for thermally detecting a defect in a test sample of a product, comprising
means for recording infrared data of a reference sample that does not have defects at ambient and elevated temperatures and for recording infrared data of the test sample at ambient and elevated temperatures; -
means for forming a reference sample difference record from the infrared data of the reference sample at the ambient and elevated temperatures, and for forming a test sample difference record from the infrared data of the test sample at the ambient and elevated temperatures; means for deriving at least one ratio from two of four difference records comprising said reference sample and test sample difference records; means for converting the ratio into a composite record involving all the difference records; and means for generating a defect indication when the composite record yields a statistically significant deviation from an expected value. - View Dependent Claims (18, 19, 20)
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21. A method of detecting defects in a test sample of a product, comprising the steps of:
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generating a reference record for at least one reference sample of the product that does not have defects, comprising the sub-steps of; (1) making an ambient-temperature thermograph of the reference sample at ambient temperature; (2) making a plurality of elevated temperature thermographs of the reference sample at a plurality of respective elevated temperatures, including applying a respective thermal stimulus to the reference sample, and (3) making a first difference record for the reference sample from the ambient-temperature thermograph and one of the plurality of elevated temperature thermographs and a second difference record for the reference sample involving at least another of the plurality of elevated temperature thermographs, the first and second difference records each comprising a plurality of image-type data points in an image-related array, generating first and second difference records for the test sample by repeating sub-steps (1)-(3) with the test sample replacing the reference sample; deriving at least one second ratio record from the four difference records consisting of the first and second difference records for the reference sample and the first and second difference records for the test sample, the ratio record including data points corresponding to respective data points in at least one of the difference records; generating a defect indication when the composite record has at least one discrete region of substantially greater than average contrast with respect to surrounding regions. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28)
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29. A method of detecting a defect in a test sample of a product, comprising the steps of:
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establishing a reference record for at least one reference sample of the product that does not have defects, comprising the sub-steps of; (1) making a base thermograph of the reference sample at a base value of a thermal stimulus; (2) making a plurality of changed value thermographs of the reference sample at a plurality of respective changed values of the thermal stimulus, including applying a respective changed-value thermal stimulus to the reference sample; and (3) making a first difference record for the reference sample from the base-value thermograph and one of the plurality of elevated value thermographs and a second difference record for the reference sample involving at least another of the plurality of elevated value thermographs, the first and second difference records each comprising a plurality of image-type data points in an image-related array; generating first and second difference records for the test sample by repeating sub-steps (1)-(3) with the test sample replacing the reference sample; deriving at least one ratio record from the four difference records consisting of the first and second difference records for the reference sample and the first and second difference records for the test sample, the ratio record including data points corresponding to the respective data points in at least one of the difference records; forming a composite record including at least the one derived ratio record; and generating a defect indication when the composite record has at least one discrete region of substantially greater than average contrast with respect to surrounding regions. - View Dependent Claims (30, 31, 32)
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33. A method of detecting a defect in a test sample of a product, comprising the steps of:
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establishing a reference record for at least one reference sample of the product that does not have defects, comprising the sub-steps of; (1) making an ambient-temperature thermograph of the reference sample at ambient temperature, (2) making a plurality of elevated temperature thermographs of the reference sample at a plurality of respective voltages applied to the sample to produce heating therein, including applying a respective voltage to the reference sample; (3) making a first difference record from the ambient-temperature thermographs and one of the plurality of elevated temperature thermographs and a second difference record involving at least another of the plurality of elevated temperature thermographs, the first and second difference records each comprising a plurality of image-type data points in an image-related array; generating a test record for the test sample by repeating sub-steps (1)-(3) with the test sample replacing the reference sample; (4) deriving at least one ratio record from the four difference records consisting of the first and second difference records for the test sample and the first and second difference records for the reference sample, the ratio record including data points corresponding to respective data points in at least one of the difference records; forming a composite record including the at least one ratio record; and generating a defect indication when the composite record has at least one discrete region of substantially greater than average contrast with respect to surrounding regions. - View Dependent Claims (34, 35, 36)
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37. A system for thermally detecting a defect in a test sample of a product, comprising
means for forming infrared images of a reference sample that does not have defects at ambient and elevated temperatures and for forming infrared images of the test sample at ambient and elevated temperatures, each of the images comprising a plurality of image data points; -
means for forming reference sample difference records from the images of the reference sample at the ambient and elevated temperatures, and for forming test sample difference records from the images of the test sample at the ambient and elevated temperatures; means for forming at least one ratio record from two of four difference records comprising said reference sample difference records and test sample difference records; means for converting the ratio record into a composite record involving all the difference records; and means for generating a defect indication when the composite record has at least one discrete region of substantially greater than average contrast with respect to surrounding regions. - View Dependent Claims (38, 39, 40)
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Specification