Optics: measuring and testing – By configuration comparison
Reexamination Certificate
1998-08-26
2001-04-24
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By configuration comparison
C237S049000, C237S049000
Reexamination Certificate
active
06222630
ABSTRACT:
This invention relates generally to automated inspection systems, and more particularly to automated optical inspection systems for inspecting printed circuit board assemblies.
Printed circuit board assemblies are typically inspected during manufacturing processes to determine whether the assemblies contain defects. In this way, defective assemblies can be identified before they are incorporated into electronic products, thereby minimizing the chance that the electronic products will fail prematurely in the field.
One type of printed circuit board inspection system that has gained wide acceptance in industry uses a technology known as automated optical inspection (AOI). One such AOI system is the INTERSCAN™ inspection system, sold by TERADYNE®, Inc., Walnut Creek, Calif., USA. This system generally uses a plurality of cameras mounted in an inspection head for capturing images of a board under inspection (BUI). The inspection head is generally supported and moved in a defined plane by an X-Y table. The system also generally uses a lighting fixture mounted in the inspection head for selectively illuminating portions of the BUI. By moving the inspection head relative to the BUI, various portions of the BUI can therefore be illuminated and images of the BUI can be captured for subsequent analysis by a test computer, which is also included in the system. Any defects found during the analysis are then reported to a human operator for appropriate correction.
Details about the general structure and operation of the inspection head, the X-Y table, and the cameras included in the INTERSCAN™ inspection system can be obtained by referring to U.S. Pat. No. 5,245,421 assigned to Control Automation Incorporated, Princeton, N.J., USA. Further, details about the general structure and operation of the lighting fixture included in the INTERSCAN™ inspection system can be obtained by referring to U.S. Pat. No. 5,060,065 assigned to Cimflex Teknowledge Corporation, Princeton, N.J., USA.
In particular, the INTERSCAN™ inspection system has traditionally included four cameras, which are arranged conically and disposed off the central axis of the inspection head such that they protrude toward the BUI. The cameras typically deviate from the central axis by an angle of about 30°. This arrangement generally enhances the capture of light reflected from components attached to the BUI and minimizes the affects of back-scattered light from the BUI. Accordingly, images of four different views of each component may be captured by the angled cameras and subsequently analyzed for verifying characteristics such as the component's presence, placement, and connection to the BUI.
However, accommodations generally must be made when inspecting printed circuit board assemblies that have varying degrees of warp. This is because components attached to warped printed circuit boards may not appear in their expected locations when viewed by the four angled cameras. For example, warp in a BUI might cause some components to appear displaced from their expected locations. This can affect the accuracy of printed circuit board inspections.
For this reason, the INTERSCAN™ inspection system has traditionally included a warp-compensating unit, which is used to measure and compensate for warp during inspection of a BUI. Details of the structure and operation of a warp compensating unit can be found in U.S. Pat. No. 4,978,220 assigned to Cimflex Teknowledge Corporation, Princeton, N.J., USA.
In particular, the warp-compensating unit is preferably included in the inspection head in an axial and centrally located position. One embodiment of the warp-compensating unit includes a projector, which projects a pattern of light onto a portion of the surface of a BUI. The pattern might take the form of a “square” or a “cross.” Each of the four angled cameras then captures an image of a “horizontal” section of the square or cross from its perspective, and these horizontal sections are analyzed to determine whether they deviate from their expected locations. The amount of deviation is proportional to the amount of warp at that portion of the BUI. Once the amount of warp is measured, the expected locations of components attached to that portion of the BUI are computationally adjusted, thereby compensating for the warp. The inspection system then analyzes the BUI to determine whether it is defective.
However, the INTERSCAN™ inspection system has recently included a fifth camera located in the axial, centrally located position in the inspection head. This is because a camera in this position, protruding perpendicularly toward a BUI, has been found to be very useful for inspecting fiducials on the BUI and for enhancing the accuracy of inspections made in conjunction with the four angled cameras.
Because the fifth camera in the INTERSCAN™ inspection system has displaced the warp compensating unit in the axial and centrally located position in the inspection head, there is a need for a new way of measuring and compensating for warp when inspecting printed circuit board assemblies.
SUMMARY OF THE INVENTION
With the foregoing background in mind, it is an object of the invention to provide an inspection system that can detect and report defects on printed circuit board assemblies.
Another object of the invention is to provide an inspection system that can accurately detect defects on warped printed circuit board assemblies.
Still another object of the invention is to provide an inspection system that can accurately verify the presence, placement, and connection of components attached to warped printed circuit board assemblies.
Yet another object of the invention is to provide an inspection system that can inspect fiducials on printed circuit board assemblies.
Yet still another object of the invention is to provide an inspection system that can measure and compensate for warp in the inspection of printed circuit board assemblies.
The foregoing and other objects are achieved by providing an automated optical inspection system including an inspection head with an axial and centrally located camera and a laser mounted at an angle from the central axis of the inspection head.
In a preferred embodiment, the laser produces a laser line on the surface of a printed circuit board assembly under inspection.
According to one feature, the laser is an infrared strobe and the vertical camera is a CCD camera.
In another embodiment, the laser projects a laser line on a calibration plate. The laser line is then segmented, and the height of each segment is measured using the central camera. The measured heights are then stored. Next, the inspection head is advanced to a plurality of viewing fields on a board under inspection, and a laser line is projected onto a surface of the board under inspection within each viewing field. The laser lines are then segmented, and the height of each segment is measured and compared with corresponding stored measurements. Next, deviations from the stored measurements are ranked. One of the ranked deviations is then selected and used to compensate for warp of the board under inspection in a respective viewing field.
According to another feature, the fourth from the smallest deviation in each viewing field is selected and used to compensate for warp in that viewing field.
Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.
REFERENCES:
patent: 4978220 (1990-12-01), Abramovich et al.
patent: 0 312 046 A2 (1989-04-01), None
patent: 0 336 563 (1989-10-01), None
patent: 0 371 650 (1990-06-01), None
patent: 8-193816 (1996-07-01), None
Font Frank G.
Ratliff Reginald A.
Teradyne Legal Department
Teradyne, Inc.
LandOfFree
Measuring and compensating for warp in the inspection of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Measuring and compensating for warp in the inspection of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Measuring and compensating for warp in the inspection of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2469322