System and method for image subtraction for ball and bumped grid array inspection

• US 6,236,747 B1
• Filed: 08/14/1998
• Issued: 05/22/2001
• Est. Priority Date: 02/26/1997
• Status: Expired due to Term

• Current Assignee: Microscan Systems Inc (Omron Corporation)
• Original Assignee: Acuity Brands, Inc.
• Inventors: King, Steven Joseph, Ludlow, Jonathan Edmund
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Mariam, Daniel G.
• Application Number:
  US09/134,654
• Time in Patent Office: 1,012 Days
• Field of Search: 382/149, 382/150, 382/145, 382/219, 382/142, 382/146, 382/147, 348/86, 348/92, 356/237.1, 356/239.3, 356/239.5
• 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: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/10152 Varying illumination
• CPC Class Codes: G06T 2207/30152 Solder
• CPC Class Codes: G06T 7/0008 checking presence/absence
• CPC Class Codes: H05K 13/0813 Controlling of single components prior to mounting, e.g. orientation, component geometry H05K13/0812 takes precedence

Abstract

An inspection system and method uses a first illumination apparatus, such as 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 first captured image. The system and method then uses a second, different illumination apparatus, such as an on-axis illumination apparatus to illuminate the reflective elements. The second illumination apparatus is selected so as to illuminate unwanted reflective elements substantially the same as they are illuminated by the first illumination apparatus while illuminating the desired reflective elements differently. A second image of the object is then captured by the illumination detection device. The second image is then subtracted from the first or vice-versa by an image processor to generate a resulting image that is substantially devoid of the unwanted reflective elements, yet including the desired reflective elements, which are further analyzed using additional image analyzed techniques.

Claims

1. A method of inspecting a ball and bumped grid array to highlight desired features while masking unwanted features, said method comprising the steps of:

a. sequentially illuminating said ball and bumped grid array using first and second illumination apparatuses, said first and second illumination apparatuses selected to illuminate said unwanted features similarly and to illuminate said desired features differently;

b. capturing a first image of said ball and bumped grid array with an image capture device while said array is illuminated with said first illumination apparatus;

c. capturing a second image of said ball and bumped grid array with said image capture device while said array is illuminated with said second illumination apparatus; and

d. processing said first and second images by subtracting second image from said first image to produce a resulting image wherein said unwanted features are eliminated.

2. The method claimed in claim 1 further comprising the step of analyzing the desired features of said resulting image.

3. The method claimed in claim 1, wherein said step of illuminating said ball and bumped grid array with said first illumination apparatus comprises illuminating said array with a low angle ring illumination apparatus.

4. The method claimed in claim 3, wherein said step of illuminating said ball and bumped grid array with said second illumination apparatus comprises illuminating said array with a substantially on-axis illumination apparatus, substantially colinear with said image capture device.

5. The method claimed in claim 3, wherein said step of illuminating said ball and bumped grid array with said second illumination apparatus comprises illuminating said array with a high angle ring illumination apparatus.

6. The method claimed in claim 1, wherein said unwanted features are solder vias.

7. The method claimed in claim 1, wherein said desired features are solder balls.

8. A ball and bumped grid array inspection system comprising:

a first illumination apparatus for illuminating said ball and bumped grid array;

a second illumination apparatus for illuminating said ball and bumped grid array said second light source selected to illuminate unwanted features of said ball and bumped grid array similarly to said first illumination apparatus;

an image capture device for capturing at least first and second images of said ball and bumped gird array, said first image corresponding to said array illuminated by said first illumination apparatus and said second image corresponding to said array illuminated by said second illumination apparatus; and

an image processor for subtracting said second image from said first image to produce a resulting image substantially devoid of said unwanted features.

9. The ball and bumped grid array inspection system of claim 8, wherein said first illumination apparatus comprises a low angle ring illumination apparatus.

10. The ball and bumped grid array inspection system of claim 8, wherein said second illumination apparatus comprises a substantially on-axis illumination apparatus, substantially colinear with said image capture device.

11. The ball and bumped grid array inspection system of claim 8, wherein said image capture device comprises a charged coupled device (CCD) camera.

12. The ball and bumped grid array inspection system of claim 11, wherein said first and second images of said array comprise grey-scale images.

13. The ball and bumped grid array inspection system of claim 8 further comprising at least a third illumination apparatus for illuminating said ball and bumped grid array, said at least a third illumination apparatus selected to illuminate additional unwanted features of said array in a manner similar to said second illumination apparatus, wherein said image capture device captures a third image of said array when said array is illuminated by said third illumination apparatus and said image processor further subtracts said third image from said resulting image to produce a further resulting image, which is substantially devoid of said additional unwanted features.

14. A method of inspecting an article to highlight desired features while masking unwanted features, said method comprising the steps of:

a. sequentially illuminating said article using first and second illumination apparatuses, said first and second illumination apparatuses selected to illuminate said unwanted features similarly and to illuminate said desired features differently;

b. capturing a first image of said article with an image capture device while said article is illuminated with said first illumination apparatus;

c. capturing a second image of said article with said image capture device while said article is illuminated with said second illumination apparatus; and

d. processing said first and second images by subtracting said second image from said first image to produce a resulting image wherein said unwanted features are eliminated.

15. The method of claim 14 further comprising the steps of:

illuminating said article with at least a third illumination apparatus, said at least a third illumination apparatus selected to illuminate additional unwanted features of said article in a manner similar to said second illumination apparatus;

capturing at least a third image of said article with said image capture device while said article is illuminated with said third illumination apparatus; and

subtracting said at least a third image from said resulting image using an image processor to produce a further resulting image, which is substantially devoid of said additional unwanted features.

16. The method of claim 14 wherein said article includes a background, and wherein said desired features and said unwanted features are both present on said background.

17. The method of claim 16 wherein said desired features and said unwanted features are both three-dimensional reflective features.