Inspection method

• US 5,926,557 A
• Filed: 03/26/1997
• Issued: 07/20/1999
• Est. Priority Date: 02/26/1997
• Status: Expired due to Term

• Current Assignee: Microscan Systems Inc (Omron Corporation)
• Original Assignee: Acuity Brands, Inc.
• Inventors: Schurr, George, Ludlow, Johathan Edmund, King, Steven Joseph
• Primary Examiner(s): Kelley, Christopher S.
• Application Number:
  US08/824,173
• Time in Patent Office: 846 Days
• Field of Search: 382/141, 382/146, 382/149-151, 382/199, 382/221, 348/86, 348/90, 348/92, 348/126, 356/237, 356/376
• US Class Current: 382/149
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: G01N 21/95684 Patterns showing highly reflecting parts, e.g. metallic elements
• CPC Class Codes: H05K 13/0817 Monitoring of soldering processes inspection of solder joints or of printed solder paste G01N21/95684

Abstract

An inspection system and method uses a ring illumination apparatus to illuminate one or more reflective elements, such as solder balls on an electronic component or other protruding surfaces or objects. The ring illumination apparatus includes a substantially ring-shaped light source that provides a substantially even illumination across the one or more reflective elements. An illumination detection device detects light beams reflecting off of the illuminated reflective elements for forming a reflected image. A method of processing the reflected image includes locating one or more points on each reflected image element representing an illuminated reflective element. The points on the reflected image elements are used to located the pattern of the reflected image elements and/or to fit an outline around each image element corresponding to a known percentage of the true dimensions of each solder ball or other reflective element. The inspection system and method thereby determines various characteristics such as the absence/presence, location, pitch, size and shape of each reflective element.

Claims

1. A method of processing a reflected image including a pattern of reflected image elements representing a pattern of illuminated generally spherical reflective elements on an article, said method comprising the steps of:

locating said pattern of reflected image elements in said reflected image;

dividing at least one reflected image element into a plurality of pixels, each pixel having a gray scale value corresponding to an intensity level of reflected light in said reflected image element;

positioning vectors across said at least one reflected image element;

examining a series of pixels along each of said vectors to locate at least four points around said at least one reflected image element;

fitting a circle around each of said at least four points located on said at least one reflected image element, wherein said circle corresponds to a known percentage of a true diameter of said generally spherical reflective element; and

determining inspection information pertaining to said at least one illuminated generally spherical reflective element represented by said at least one reflected image element using dimensions of said circle fit around each of said at least four points located on said at least one reflected image element.

2. The method of claim 1 wherein said step of locating said pattern of reflected image elements includes:

locating at least one group of reflected image elements;

locating at least one point on each reflected image element in said at least one group of reflected image elements; and

fitting a line to said at least one point of said reflected image elements in said at least one group of reflected image elements, for determining at least an expected location of each said reflected image element in said reflected image.

3. The method of claim 2

wherein the step of examining said series of pixels along said vectors includes:

determining an intensity gradient at each pixel in said series of pixels along said vectors positioned across each of said at least one reflected image element; and

responsive to said step of determining an intensity gradient, locating a point of maximum intensity gradient along said vectors positioned across each of said reflected image elements, wherein said point of maximum intensity gradient corresponds to an outside edge of each said at least one reflected image element.

4. The method of claim 3 further including the steps of locating a group of points of maximum intensity gradient, and fitting an ellipse to said group of points of maximum intensity gradient, wherein a peak of said ellipse corresponds to said outside edge of said reflected image element with sub-pixel accuracy.

5. The method of claim 2

wherein the step of examining said series of pixels along said vectors includes:

locating a pixel of maximum gray scale value along said vectors positioned across each of said at least one reflected image element, wherein said pixel of maximum gray scale value corresponds to a brightest midpoint of each said reflected image element.

6. The method of claim 5 further including the steps of locating a group of pixels of maximum gray scale value, and fitting an ellipse to said group of pixels of maximum gray scale value, wherein a peak of said ellipse corresponds to said brightest midpoint of said reflected image element with sub-pixel accuracy.

7. The method of claim 1 wherein the step of determining inspection information includes calculating a diameter of each generally spherical reflective surface using said circle fitted around said at least four points on said reflected image element.

8. The method of claim 1 wherein determining inspection information includes calculating a circularity of each generally spherical reflective surface using said circle fitted around said at least four points on said reflected image element.

9. The method of claim 1 further including the step of determining a count of the number of said reflected image elements in said array.

10. The method of claim 9 wherein determining the count of the number of said reflected image elements in said array includes:

locating groups of pixels having a gray scale value above a threshold gray scale value; and

counting the number of said groups of pixels to determine said count of the number of said reflected image elements, wherein said count of the number of said reflected image elements corresponds to a count of the number of illuminated reflective elements.

11. The method of claim 10 wherein said step of determining inspection information includes:

comparing said count of the number of said reflected image elements to an expected count of the number of said illuminated reflective element; and

determining an absence/presence of at least one said illuminated reflective element.

12. A method of processing a reflected image including a pattern of reflected image elements representing a pattern of illuminated reflective elements on an article, said method comprising the steps of:

locating said pattern of reflected image elements in said reflected image;

locating at least one point on at least one reflected image element in said pattern of reflected image elements, wherein the step of locating said at least one point on said at least one reflected image element includes;

dividing said at least one reflected image element into a plurality of pixels, each pixel having a gray scale value corresponding to an intensity level of reflected light in said at least one reflected image element;

positioning at least one vector across said at least one reflected image element;

examining a series of pixels along said at least one vector;

determining an intensity gradient at each pixel in said series of pixels along said at least one vector positioned across said at least one reflected image element; and

responsive to said step of determining an intensity gradient, locating a point of maximum intensity gradient along said at least one vector positioned across said at least one reflected image element, wherein each said point of maximum intensity gradient corresponds to an outside edge of said at least one reflected image element; and

determining inspection information pertaining to at least one illuminated reflective element represented by said at least one reflected image element using said at least one point located on said at least one reflected image element.

13. The method of claim 12 wherein said step of locating at least one point includes locating a plurality of points on said at least one reflected image element, and further including fitting a line through each of said plurality of points and generally around said at least one reflected image element.

14. The method of claim 13 wherein said at least one illuminated reflective element has a generally spherical shape, and wherein said at least one reflected image element has a generally circular shape.

15. The method of claim 14 wherein said step of locating at least one point includes locating at least four points on said at least one reflected image element, wherein said step of fitting said line includes fitting a circle through said at least four points and generally around said at least one reflected image element, and wherein determining inspection information includes calculating at least one of a diameter and a circularity of said at least one illuminated reflective element corresponding to said at least one reflected image element using dimensions of said circle.

16. A method of processing a reflected image including a pattern of reflected image elements representing a pattern of illuminated, generally spherical reflective elements on an article, said method comprising the steps of:

locating said pattern of reflected image elements in said reflected image;

locating at least one point on at least one reflected image element in said pattern of reflected image elements, wherein the step of locating said at least one point on said at least one reflected image element includes;

dividing said at least one reflected image element into a plurality of pixels, each pixel having a gray scale value corresponding to an intensity level of reflected light in said reflected image element;

positioning at least one vector across said at least one reflected image element;

examining a series of pixels along said at least one vector;

locating a pixel of maximum gray scale value along said at least one vector positioned across said at least one reflected image element, wherein said pixel of maximum gray scale value corresponds to a brightest midpoint of said at least one reflected image element and corresponds to a known location on at least one illuminated generally spherical reflective element represented by said at least one reflected image element; and

determining inspection information pertaining to said at least one illuminated generally spherical reflective element represented by said at least one reflected image element using said at least one point located on said at least one reflected image element.

17. The method of claim 16 wherein said step of locating at least one point includes locating a plurality of points on said at least one reflected image element, and further including fitting a line through each of said plurality of points and generally around said at least one reflected image element.

18. The method of claim 17 wherein said at least one reflected image element has a generally circular shape.

19. The method of claim 18 wherein said step of locating at least one point includes locating at least four points on said at least one reflected image element, wherein said step of fitting said line includes fitting a circle through said at least four points and generally around said at least one reflected image element, and wherein determining inspection information includes calculating at least one of a diameter and a circularity of said at least one illuminated generally spherical reflective element corresponding to said at least one reflected image element using dimensions of said circle.