Automatic X-ray determination of solder joint and view Delta Z values from a laser mapped reference surface for circuit board inspection using X-ray laminography

• US 6,665,433 B2
• Filed: 10/16/2002
• Issued: 12/16/2003
• Est. Priority Date: 07/31/2001
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Roder, Paul A.
• Primary Examiner(s): Ahmed, Samir
• Assistant Examiner(s): Bali, Vikkram
• Application Number:
  US10/272,263
• Publication Number:
  US 20030035576A1
• Time in Patent Office: 426 Days
• Field of Search: 382/141, 382/143, 382/144-151, 382/106, 382/154, 382/199, 348/86, 348/87, 348/125, 348/126, 702/57, 702/58, 702/59
• US Class Current: 382/147
• CPC Class Codes: G06T 2207/30141 Printed circuit board [PCB]
• CPC Class Codes: G06T 2207/30152 Solder
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light
• CPC Class Codes: G06T 7/571 from focus

Abstract

An improved circuit board inspection system incorporates self learning techniques for accurate determination of Z-axis elevations of electrical connections. A Delta Z, referenced to a laser range finder generated surface map of the circuit board, is automatically determined from a series of cross sectional images of the electrical connections for each electrical connection on the circuit board. The Delta Z values for each electrical connection are stored in a data base from which customized Delta Z values for specifically defined board views may be calculated.

Claims

1. A device for inspecting electrical connections on a circuit board comprising:

a processor which controls the acquisition of a cross-sectional image of a cutting plane of the electrical connection at an image plane and analyzes said cross-sectional image, said processor configured to implement the following;

a Z-axis controller for varying a Delta Z value, i.e., the Z-axis distance between the image plane and a reference Z-axis position, and acquiring a plurality of Delta Z images of the electrical connection at a plurality of said Delta Z values;

an image gradient section which calculates and stores a plurality of gradients for each of said plurality of Delta Z images;

a variance calculator section which determines a variance of said plurality of gradients for each of said plurality of Delta Z images; and

a comparator which compares said variances of said gradients for each of said plurality of Delta Z images.

2. A device as defined in claim 1 further comprising a surface mapper for creating a surface map of the circuit board.

3. A device as defined in claim 2 wherein said surface mapper further comprises a laser range finder for determining reference Z-axis values for a plurality of points on the circuit board thereby creating a laser surface map of the circuit board.

4. A device as defined in claim 1 wherein said image gradient is approximated over a K×

K pixel grid by the following relation;

5. A device as defined in claim 1 wherein said comparator further comprises means for fitting said variances of said plurality of gradients for each of said plurality of Delta Z images with either one of a parabolic curve or a Gaussian curve.

6. A device as defined in claim 5 wherein said comparator further comprises means for determining a Delta Z value corresponding to a maximum value of said parabolic curve or said Gaussian curve.

7. A device as defined in claim 1 wherein said processor further comprises an image section which produces said cross-sectional image of a cutting plane of said electrical connection from said image database.

8. The device as defined in claim 1,

a source of X-rays which emits X-rays through the electrical connection from a plurality of positions;

an X-ray detector positioned to receive the X-rays produced by said source of X-rays which have penetrated the electrical connection, said X-ray detector further comprising an output which emits data signals corresponding to an X-ray image of the electrical connection produced by the X-rays received and detected by said X-ray detector after penetrating the electrical connection; and

a memory which stores said detector data signals and an image database which contains information sufficient to form the cross-sectional image.