Method and apparatus to locate and measure capillary indentation marks on wire bonded leads

• US 5,835,622 A
• Filed: 08/31/1995
• Issued: 11/10/1998
• Est. Priority Date: 05/02/1994
• Status: Expired due to Term

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Petry, John P. III, Koljonen, Juha
• Primary Examiner(s): CHANG, JON CARLTON
• Application Number:
  US08/520,935
• Time in Patent Office: 1,167 Days
• Field of Search: 382/150, 382/141, 382/168, 382/151, 382/174, 382/146, 382/291, 382/170, 382/209, 382/217, 382/218, 348/126, 348/94, 348/95, 348/87
• US Class Current: 382/146
• CPC Class Codes: G06T 2207/30152 Solder
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/62 of area, perimeter, diameter or volume
• CPC Class Codes: G06T 7/66 of image moments or centre of gravity
• CPC Class Codes: G06T 7/70 Determining position or orientation of objects or cameras camera calibration G06T7/80
• CPC Class Codes: G06V 10/48 by mapping characteristic values of the pattern into a parameter space, e.g. Hough transformation

Abstract

A method and apparatus for locating and measuring capillary indentation marks on wire bonded leads by creating a normalized, one-dimensional circumferential projection of a candidate center location in an image of a capillary indentation mark and detecting signals in the one-dimensional circumferential projection that correspond to a predefined pattern. The one-dimensional circumferential projection can be generated and evaluated for a full or a sub-sampled set of candidate center locations according to a number of different methods.

Claims

1. In a system capable of acquiring, digitizing and analyzing an image a method for locating and measuring a capillary indentation mark on a wire bonded lead, comprising the steps of:

selecting a candidate center location in said image;

creating a one-dimensional circumferential projection for said candidate center location such that a bin of said one-dimensional circumferential projection contains a normalized pixel intensity value for the circumference of an expected shape at said candidate center location;

detecting signals in said one-dimensional circumferential projection that correspond to a predefined pattern for a capillary indentation mark; and

storing the results of said detecting step, so that as each candidate center location is evaluated, the candidate center location with the one-dimensional circumferential projection having the best fit is deemed the center of said capillary indentation mark, and the distance from said candidate center location with the one-dimensional circumferential projection having the best fit to its edge is deemed to be the radius of said capillary indentation mark, thus locating and measuring said capillary indentation mark.

2. The method of claim 1, wherein said detecting step further comprises the step of using an edge filter to locate high contrast edges in said one-dimensional circumferential projection.

3. The method of claim 1, wherein said selecting step further comprises selecting every n candidate center location in said image to evaluate, where n is a sub-sampling rate supplied by the user of said system.

4. In a system capable of acquiring, digitizing and analyzing an image, a method for locating and measuring a capillary indentation mark on a wire bonded lead, comprising the steps of:

selecting a candidate center location in said image;

creating a one-dimensional circumferential projection for said candidate center location such that each bin (BIN) of said one-dimensional circumferential projection contains a normalized pixel intensity value(I) for each circle at a selected radius(R) in said candidate center location calculated as follows;

##EQU4## where I(R, φ

) is the pixel intensity value at location R,φ

in polar coordinates;

detecting edges in said one-dimensional circumferential projection that correspond to a predefined pattern for a capillary indentation mark; and

storing the results of said detecting step, so that as each candidate center location is evaluated, the candidate center location with the one-dimensional circumferential projection having the best fit is deemed the center of said capillary indentation mark, and the distance from said candidate center location with the one-dimensional circumferential projection having the best fit to its edge is deemed to be the radius of said capillary indentation mark, thus locating and measuring said capillary indentation mark.

5. The method of claim 4 wherein said detecting step further comprises the step of using an edge filter to locate high contrast edges in said one-dimensional circumferential projection.

6. The method of claim 4, wherein said selecting step further comprises selecting every n candidate center location in said image to evaluate, where n is a sub-sampling rate supplied by the user of said system.

7. In a system capable of acquiring, digitizing and analyzing an image, a method for locating and measuring a capillary indentation mark on a wire bonded lead, comprising the steps of:

selecting a candidate center location in said image;

generating a two-dimensional polar destination image using a polar unwrap;

creating a one-dimensional circumferential projection by summing along an axis of said two-dimensional polar destination image of said candidate center location such that each bin of said one-dimensional circumferential projection contains a normalized pixel intensity value for each circle at a selected radius in said candidate center location;

detecting edges in said one-dimensional circumferential projection that correspond to a predefined pattern for a capillary indentation mark; and

storing the results of said detecting step, so that as each candidate center location is evaluated, the candidate center location with the one-dimensional circumferential projection having the best fit is deemed the center of said capillary indentation mark, and the distance from said candidate center location with the one-dimensional circumferential projection having the best fit to its edge is deemed to be the radius of said capillary indentation mark, thus locating and measuring said capillary indentation mark.

8. The method of claim 7 wherein said detecting step further comprises the step of using an edge filter to locate high contrast edges in said one-dimensional circumferential projection.

9. The method of claim 7 wherein said selecting step further comprises selecting every n candidate center location in said image to evaluate, where n is a sub-sampling rate supplied by the user of said system.

10. In a system capable of acquiring, digitizing andanalyzing an image, a method for locating and measuring a capillary indentation mark on a wire bonded lead, comprising the steps of:

constructing an transform image (It) having a center located at xc, yc and a size and radius value larger than the maximum size and radius values of a selected ring of an expected capillary indentation mark to be measured, using the following formula;

##EQU5## selecting a candidate center location in said image;

aligning the center of said transform image with said candidate center location so that each x, y coordinate of said candidate center location corresponds to an x, y location in said transform image; and

evaluating said candidate center location and said transform image simultaneously, whereby each pixel value in said candidate center location is summed into a one-dimensional circumferential projection indexed by the pixel value at the corresponding x,y coordinate in said transform image, such that a one-dimensional histogram is created and stored in said one-dimensional circumferential projection, said one-dimensional circumferential projection having a number of bins equal to the maximum radius size of said selected ring of said expected capillary indentation mark wherein each bin has indexes ranging from zero to said maximum radius size of said transform image; and

detecting edges in said one-dimensional circumferential projection that correspond to a predefined pattern for a capillary indentation mark; and

storing the results of said detecting step, so that as each candidate center location is evaluated, the candidate center location with the one-dimensional circumferential projection having the best fit is deemed the center of said capillary indentation mark, and the distance from said candidate center location with the one-dimensional circumferential projection having the best fit to its edge is deemed to be the radius of said capillary indentation mark, thus locating and measuring said capillary indentation mark.

11. The method of claim 10 wherein said detecting step further comprises the step of using an edge filter to locate high contrast edges in said one-dimensional circumferential projection.

12. The method of claim 10 wherein said selecting step further comprises selecting every n candidate center location in said image to evaluate, where n is a sub-sampling rate supplied by the user of said system.

13. The method of claim 10, wherein the step of constructing an transform image further comprises dividing said transform image into quadrants by adding a first constant pixel value to pixels in a first quadrant, a second constant pixel value to pixels in a second quadrant, a third constant pixel value to pixels in a third quadrant and a fourth constant pixel value to pixels in a fourth quadrant.

14. The method of claim 10, wherein said step of evaluating said candidate center location and said transform image simultaneously further comprises:

generating four one-dimensional circumferential projections, each representing one of said quadrants, such that four radiuses are located and their respective differences from an expected capillary indentation mark center location can be reported in the x and y directions.

15. In a system capable of acquiring, digitizing and analyzing an image, an apparatus for locating and measuring a capillary indentation mark on a wire bonded lead, comprising:

means for selecting a candidate center location in said image,;

means for creating a one-dimensional circumferential projection for said candidate center location such that each bin of said one-dimensional circumferential projection contains a normalized pixel intensity value for each circle at a selected radius in said candidate center location;

means for detecting edges in said one-dimensional circumferential projection that correspond to a predefined pattern for a capillary indentation mark; and

means for storing the results found by said means for detecting edges, so that as each candidate center location is evaluated, the candidate center location with the one-dimensional circumferential projection having the best fit is deemed the center of said capillary indentation mark, and the distance from said candidate center location with the one-dimensional circumferential projection having the best fit to its edge is deemed to be the radius of said capillary indentation mark, thus locating and measuring said capillary indentation mark.

16. The apparatus of claim 15, wherein said means for detecting edges further comprises an edge filter means used to locate high contrast edges in said one-dimensional circumferential projection.

17. The apparatus of claim 15, wherein said means for selecting a candidate center location further comprises a means for selecting every n candidate center location in said image to evaluate, where n is a sub-sampling rate supplied by the user of said system.

18. In a system capable of acquiring, digitizing and analyzing an image, an apparatus for locating and measuring a capillary indentation mark on a wire bonded lead, comprising:

means for selecting a candidate center location in said image;

means for creating a one-dimensional circumferential projection for said candidate center location such that each bin (BIN) of said one-dimensional circumferential projection contains a normalized pixel intensity value(I) for each circle at a selected radius(R) in said candidate center location calculated as follows;

##EQU6## where I(R, φ

) is the pixel intensity value at location R,φ

in polar coordinates;

means for detecting edges in said one-dimensional circumferential projection that correspond to a predefined pattern for a capillary indentation mark; and

means for storing the results of said means for detecting edges, so that as each candidate center location is evaluated, the candidate center location with the one-dimensional circumferential projection having the best fit is deemed the center of said capillary indentation mark, and the distance from said candidate center location with the one-dimensional circumferential projection having the best fit to its edge is deemed to be the radius of said capillary indentation mark, thus locating and measuring said capillary indentation mark.

19. The apparatus of claim 18 wherein said means for detecting edges further comprises an edge filter means to locate high contrast edges in said one-dimensional circumferential projection.

20. The apparatus of claim 18, wherein said means for selecting a candidate center location further comprises means for selecting every n candidate center location in said image to evaluate, where n is a sub-sampling rate supplied by the user of said system.

21. In a system capable of acquiring, digitizing and analyzing an image, an apparatus for locating and measuring a capillary indentation mark on a wire bonded lead, comprising:

means for selecting a candidate center location in said image;

means for generating a two-dimensional polar destination image using polar unwrap to map pixel intensity values in said candidate center location into normalized pixel intensity values in a polar destination image;

means for creating a one-dimensional circumferential projection for said candidate center location by summing along an axis of said two-dimensional polar destination image such that each bin of said one-dimensional circumferential projection contains a normalized pixel intensity value for each circle at a selected radius in said candidate center location;

means for detecting edges in said one-dimensional circumferential projection that correspond to a predefined pattern for a capillary indentation mark; and

means for storing the results of said means for detecting edges, so that as each candidate center location is evaluated, the candidate center location with the one-dimensional circumferential projection having the best fit is deemed the center of said capillary indentation mark, and the distance from said candidate center location with the one-dimensional circumferential projection having the best fit to its edge is deemed to be the radius of said capillary indentation mark, thus locating and measuring said capillary indentation mark.

22. The apparatus of claim 21 wherein said means for detecting edges further comprises an edge filter means to locate high contrast edges in said one-dimensional circumferential projection.

23. The apparatus of claim 21 wherein said means for selecting a candidate center location further comprises means for selecting every n candidate center location in said image to evaluate, where n is a sub-sampling rate supplied by the user of said system.

24. In a system capable of acquiring, digitizing and analyzing an image, an apparatus for locating and measuring a capillary indentation mark on a wire bonded lead, comprising:

means for constructing an transform image (It) having a center located at xc, yc and a size and radius value larger than the maximum size and radius values of a selected ring of an expected capillary indentation mark to be measured, using the following formula;

##EQU7## means for selecting a candidate center location in said image,;

means for aligning the center of said transform image with said candidate center location so that each x, y coordinate of said candidate center location corresponds to an x, y location in said transform image; and

means for evaluating said candidate center location and said transform image simultaneously, whereby each pixel value in said candidate center location is summed into a one-dimensional circumferential projection indexed by the pixel value at the corresponding x,y coordinate in said transform image, such that a one-dimensional histogram is created and stored in said one-dimensional circumferential projection, said one-dimensional circumferential projection having a number of bins equal to the maximum radius size of said selected ring of said expected capillary indentation mark wherein each bin has indexes ranging from zero to said maximum radius size of said transform image; and

means for detecting edges in said one-dimensional circumferential projection that correspond to a predefined pattern for a capillary indentation mark; and

means for storing the results of said means for detecting edges, so that as each candidate center location is evaluated, the candidate center location with the one-dimensional circumferential projection having the best fit is deemed the center of said capillary indentation mark, and the distance from said candidate center location with the one-dimensional circumferential projection having the best fit to its edge is deemed to be the radius of said capillary indentation mark, thus locating and measuring said capillary indentation mark.

25. The apparatus of claim 24 wherein said means for detecting edges further comprises an edge filter means to locate high contrast edges in said one-dimensional circumferential projection.

26. The apparatus of claim 24 wherein said means for selecting a candidate center location further comprises means for selecting every n candidate center location in said image to evaluate, where n is a sub-sampling rate supplied by the user of said system.

27. the apparatus of claim 24, wherein said means for constructing an transform image further comprises dividing said transform image into quadrants by adding a first constant pixel value to pixels in a first quadrant, a second contrast pixel value to pixels in a second quadrant, a third constant pixel value to pixels in a third quadrant and a fourth constant pixel value to pixels in a fourth quadrant.

28. The apparatus of claim 24, wherein said means for evaluating said candidate center location and said transform image simultaneously further comprises means for generating four one-dimensional circumferential projection, each representing one of said quadrants, such that four radiuses are located and their respective differences from an expected capillary indentation mark center location can be reported in the x and y directions.