Learning method and apparatus for detecting and controlling solder defects

• US 5,621,811 A
• Filed: 02/04/1994
• Issued: 04/15/1997
• Est. Priority Date: 10/30/1987
• Status: Expired due to Term

• Current Assignee: Keysight Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Baker, Bruce D., Corey, Robert L., Ross, Edward W., Adams, John A., Roder, Paul A.
• Primary Examiner(s): COUSO, YON JUNG
• Application Number:
  US08/192,413
• Time in Patent Office: 1,166 Days
• Field of Search: 382/144, 382/145, 382/147, 382/149, 382/150, 348/87, 348/86, 348/125, 348/126, 348/129, 378/22, 378/23
• US Class Current: 382/147
• CPC Class Codes: G01N 23/043 using fluoroscopic examination, with visual observation or video transmission of fluoroscopic images
• CPC Class Codes: G01N 23/044 using laminography or tomosynthesis
• CPC Class Codes: G01R 31/302 Contactless testing G01R31/66 takes precedence
• CPC Class Codes: G01R 31/304 of printed or hybrid circuits G01R31/305 - G01R31/315 take precedence
• CPC Class Codes: G01R 31/311 of integrated circuits G01R31/31728 takes precedence

Abstract

A method and apparatus which incorporate self learning techniques for the detection of solder defects and for statistical process control of solding operations on printed circuit board assemblies (PCBA) are disclosed. The invention includes learning techniques which are used during the inspection of cross-sectional X-ray images of solder joints. These learning techniques improve measurement accuracy by accounting for localized shading effects, which can occur when inspecting double-sided printed circuit board assemblies. Two specific examples are discussed. The first is a method for detection of solder short defects. The second method utilizes learning to improve the accuracy of statistical process control (SPC) measurements.

Claims

1. A method of determining the quality of an electrical connection comprising the steps of:

acquiring a cross sectional image of a cutting plane of an electrical connection on a first circuit board;

defining a region of interest proximate the electrical connection on the first circuit board;

measuring a characteristic of the region of interest on said first circuit board and storing said measured characteristic;

acquiring a cross sectional image of a cutting plane of an electrical connection on a second circuit board; and

calculating a correction factor for said cross sectional image of a cutting plane of said electrical connection on said second circuit board which is a function of said measured characteristic.

2. An apparatus for determining the quality of an electrical connection comprising:

an imaging system for producing a first cross-sectional image of a cutting plane of a first electrical connection and a second cross-sectional image of a cutting plane of a second electrical connection; and

an image analysis system for analyzing said first and second cross-sectional images, said image analysis system further comprising;

a learning processor which acquires a predetermined image characteristic of said first cross-sectional image;

a correction processor which uses said predetermined image characteristic of said first cross-sectional image to modify said second cross-sectional image; and

a test processor which performs a predetermined test on said modified second cross-sectional image to determine the quality of said second electrical connection.

3. A method of detecting solder bridging defects on a circuit board comprising the steps of:

acquiring a first cross sectional image of a cutting plane of a first electrical connection which does not have a bridging defect;

defining a background around said first electrical connection in said first cross sectional image;

acquiring a second cross sectional image of a cutting plane of a second electrical connection;

removing said background from said second cross sectional image of a cutting plane of said second electrical connection to produce a background corrected image;

comparing the image intensities comprising said background corrected image to a predetermined threshold image intensity level; and

identifying locations on said background corrected image where the image intensities exceed said threshold image intensity level.

4. An apparatus for monitoring a solder application device which forms solder joints, said apparatus comprising:

a solder joint inspection device which determines the thickness of each of said solder joints wherein said solder joint inspection device comprises;

an imager that produces cross-sectional images of cutting planes of solder joints;

a background compensator which removes a model background from said cross-sectional images of cutting planes of solder joints; and

an image analyzer which analyzes said cross-sectional images with the model background removed to determine the thickness of each of said solder joints; and

a memory which records said determined solder thickness.

5. A method for inspecting a printed circuit board, said method comprising the steps of:

producing a cross-sectional image of a cutting plane of a first printed circuit board;

measuring background image intensity levels at predetermined locations of said image of said first printed circuit board;

producing a cross-sectional image of a cutting plane of a second printed circuit board having the same design as said first printed circuit board; and

removing said first printed circuit board background image intensity levels from said image of said second printed circuit board.