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Method and apparatus for inspection of substrates
| Details |
Inventors: Amir, Israel; Higgins, Frank P.;
Assignee: AT&T Bell Laboratories (Murray Hill, NJ)
Primary Examiner: Nelms; David C.
Assistant Examiner:
Attorney, Agent or Firm: Levy; Robert B.
Inspection of a circuit board (10) to detect missing and misaligned active and passive surface-mounted components (12) and (14), respectively, is accomplished by first illuminating the board with top light to enhance the image of the passive components. The circuit board is then displaced, relative to a linescan camera (28) trained on the board, so that the camera captures the image of successive strips of surface area running across the board perpendicular to its direction of movement. The images captured by the camera (28) are stored and thereafter processed by an image-processing system (33) to determine whether any passive component is missing or misaligned. The circuit board is then illuminated with side light to enhance the image of the active components. The circuit board is again displaced relative to the linescan camera so the camera captures the image of successive strips of surface area on the board. The captured images are stored and then processed by the image-processing system to detect whether any of the active surface-mounted components are missing or misaligned. |
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DETAILED DESCRIPTION FIG.
1 shows a conventional printed circuit board 10 which is populated with both active and passive surface-mounted components 12 and 14.
As illustrated in FIG.
2, which is an enlarged side view of the circuit board 10, each active component 12, typically, a plcc, soic, or an sot, is comprised of a pismatic body 16 having a plurality of light- reflective metal leads 18 extending from one or more of its sides.
In an exemplary embodiment, the component 12 is depicted as a plcc whose leads 18 are "J-leaded" and are tucked substantially underneath the body 18.
The passive component 14, typically a resistor or capacitor, is generally short and planar in shape.
At each end of the component 14 is a metallized pad 20 which serves as one of the component's two leads.
Referring to FIGS.
1 and 2, in addition to the components 12 and 14, the circuit board 10 also carries a plurality of fiducial marks 21, each formed of a distinctive metallized area on the surface of the board.
The fiducials 21 are situated at known locations on the surface of the circuit board 10.
Thus, the position of each of the components 12 and 14 can be determined by knowing the distance from the fiducials 21.
When fabricating the circuit board 10, it is desirable to detect whether any of the components 12 and 14 are missing or misaligned prior to their being soldered in place.
Repair of the circuit board 10 to correct these types of defects is more easily accomplished prior to soldering of the components 12 and 14 in place than afterwards.
In FIG.
1, there is shown a schematic view of a system 22, in accordance with the invention, for inspecting the circuit board 10 to detect whether any of the active and passive components 12 and 14 are missing or misaligned.
The inspection system 22 is comprised of a support 24 which seats the circuit board 10.
Suitable clamping means (not shown) are provided to hold the circuit board 10 in place on the support.
A motor 25 serves to displace the support 24 in opposite directions along an axis 26
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MEMS 
