Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K13/00—Apparatus or processes specially adapted for manufacturing or adjusting assemblages of electric components
  • H05K13/08—Monitoring manufacture of assemblages
  • H05K13/081—Integration of optical monitoring devices in assembly lines; Processes using optical monitoring devices specially adapted for controlling devices or machines in assembly lines
  • H05K13/0812—Integration of optical monitoring devices in assembly lines; Processes using optical monitoring devices specially adapted for controlling devices or machines in assembly lines the monitoring devices being integrated in the mounting machine, e.g. for monitoring components, leads, component placement

Definitions

• the invention relates to visualization of printed circuit boards and parts presenting characteristic visualization problems.
• the invention is particularly, but not exclusively, useful for recognizing by computer vision physical features of any of several types of printed circuit boards or electronic parts, where each type of board or part presents a different characteristic visualization problem.
• Automated printed circuit board assembly equipment such as the Automated Component Mounter from Assembleon, utilize computer vision systems to inspect and accurately place printed circuit boards and parts to be mounted on those boards.
• the inspection of these items typically requires visualizing an item, recognizing the physical features of the item and analyzing the physical characteristics of the physical features.
• An empty printed circuit board or card is typically picked out of a storage location and computer vision equipment, including a camera and frontal lighting, is employed by the assembly machine to inspect the physical features on the board. Certain of these physical features are called f ⁇ ducials, which are provided to precisely register the parts that will be installed on the board. Other such physical features on the circuit board are solder paste contact pads. If the inspected board is not rejected, the assembly machine then places it into position to receive parts for mounting.
• Each part to be mounted is then picked out of a storage location and computer vision equipment, again including a camera and frontal lighting, is employed by the assembly machine to inspect the part. If the part is not rejected, the assembly machine then steers the placement of the part with proper registration to its mounting position on the board or card.
• CCD charge coupled device
• aspects of the invention may be found in a method and apparatus in which a filter is automatically deployed when inspecting circuit boards and parts of a certain type.
• the filter corrects characteristic problems encountered when visualizing the physical features of items of that type.
• the contrast in a image between silver fiducials and a light colored printed circuit board, or between silver contacts and a light colored part may be improved by linearly polarizing the illumination of the circuit board and imaging the board or part through a linear polarizing filter oriented in a different direction than the illumination filter.
• the contrast between contacts of one color and a background of another color in an image of a part may be improved by imaging the part through a color filter.
• the glare in an image of a circuit board or part may be reduced by imaging the board or part through a circular-polarizing filter.
• the effect of reflected infrared radiation on a CCD camera may be reduced in an image of a circuit board or part by imaging the board or part through a filter rejecting infrared.
• an aspect of the invention may be found in the following method for visualizing an item having physical features on a background.
• the item is illuminated with electromagnetic radiation, using an illumination source.
• An image is formed of the electromagnetic radiation reflected from the item, which image has characteristic defects depending on the type of item being visualized.
• the reflected electromagnetic radiation is automatically filtered to remove the characteristic defects from the image, thereby improving the contrast between the physical features and the background in the filtered image.
• circuit board or part may be recognized in the filtered image for the purpose of inspection.
• FIG. 1 A block diagram illustrating an exemplary computing environment in accordance with the present disclosure.
• FIG. 1 A block diagram illustrating an exemplary computing environment in accordance with the present disclosure.
• FIG. 1 A block diagram illustrating an exemplary computing environment in accordance with the present disclosure.
• the filter is moved linearly into position.
• Figure 1 is a schematic elevational cross-section view of visualization, recognition and placement apparatus in accordance with the invention
• Figure 2 is a top view of illumination and reption parts of Figure 1, as viewed from the lines 2-2;
• Figure 3 is a cross-section view of visualization, recognition, placement and linear filter deployment apparatus in accordance with the invention, with the filter retracted;
• Figure 4 is a cross-section view with the filter deployed;
• Figure 5 is a cross-section view of another embodiment of the invention, showing a rotational filter deployment apparatus;
• Figure 6 is a top view of the rotational filter deployment apparatus of Figure 5.
• FIG. 1 of the drawing an embodiment of the present invention for visualization of parts having metallic objects against a dielectric or non-metallic poorly contrasting background, is explained in conjunction with a conventional computer vision system 10 recognizing a usually two dimensional Ball Grid Array (BGA) 12 of small high melt solder balls 14 carried by a ceramic dielectric substrate 16.
• BGA Ball Grid Array
• GA 12 is held by a gripper or manipulator 18 of a pick and place machine (not shown) over an upwardly looking camera 20 of computer vision system 10.
• the camera 20 forms and provides an electronic image to computer vision system 10, which system utilizes the electronic image to recognize and inspect the solder balls 14 of the BGA 12, as to existence, size and spacing. If the BGA 12 passes inspection, the vision system 10 steers the translation and placement of BGA 12 by manipulator 18 on a circuit board or card 22, with the recognized solder balls 14 of the BGA in registration with contact pads 24 of the board or card 22.
• the contact pads 24 are coated with a eutectic solder paste, and after the placement of the BGA 12 and other surface mount components on circuit board or card 22, heat is applied to card with placed BGA and other components to fuse the solder paste into fillets (not shown) firmly surface mounting the BGA to the circuit board or card.
• the light box 26 is used to provide generally upwardly and inwardly directed polarized illumination I of BGA 12, in conjunction with a polarization filter 28 in front of the lens 30 of camera 20, in order to allow for proper visualization by camera 20, and proper recognition by vision system 10 of solder balls 14.
• a preferred embodiment of light box 26 has a central aperture 32 through which camera 20 looks upward via polarization filter 28, and four upwardly and outwardly inclined trapezoidal faces 34, 36, 38, 40 of a frusto-pyramid, each face forming a separate source of polarized light.
• the faces 34, 36, 38, and 40 comprise polarization filters 40, 42, 44, and 46 over respective milk glass diffuser panels 50, over LED arrays 52.
• polarization filters 40 and 44 are oriented to pass linear polarization directed at 90° and polarization filters 42 and 46 are oriented to pass linear polarization directed at 180°.
• the result is that the downwardly directed component of light from the four sources reflected from the solder balls 14 has a polarization at 90°, which is, or is nearly, orthogonal with the polarization direction that would be passed by polarization filter 28. Therefore no light reflected by solder balls 14 reach the lens 30 of camera 20.
• the downwardly directed component of light reflected from the white or light colored substrate 16 is substantially uniformly distributed in polarization and a substantial amount of light reflected downward from the substrate 16 passes through polarization filter 28 and reaches the lens 30 of camera 20.
• the solder balls 14 appear substantially black and the substrate 16 appears substantially white, providing good contrast for reliable recognition of solder balls 14.
• This contrast producing effect is thought to be due to a preservation of polarization in reflection of electromagnetic radiation from shiny metal objects versus a the smearing of polarization in reflection of electromagnetic radiation from dielectric objects.
• a printed circuit board assembly machine will inspect parts of different types during the assembly of a single circuit board.
• Such a substrate provides good contrast with the silver or gold colored fiducials used to register the parts installed on the circuit board.
• other circuit boards or cards handled by the same assembly machine may have a white, or other light colored, ceramic substrate, which provides poor contrast with the metallic fiducials.
• the technique described above for deploying a filter when appropriate to achieve reliable recognition of solder balls on parts having either light colored or dark colored substrates can also be used to reliably recognize metallic fiducials on either light colored or dark colored printed circuit boards and cards.
• the control system of a circuit board assembly machine typically utilizes a specification file for each type of item (printed circuit board, card or part) it handles. This file contains information on the characteristics of each type of item.
• Information from that file such as the number and location of physical features (fiducials and contact pads on boards and cards, or contacts on parts), is provided to the computer vision system for the inspection process.
• the specification file would also contain information indicating whether a filter should be used when inspecting an item of that type and, for the embodiment shown in Figure 5, specifying which type of filter is to be used.
• FIG. 3 of the drawing an embodiment of the invention employing a linear filter deployment apparatus 60 is shown with the filter retracted.
• a filter 61 is attached by linkage 64 to linear actuator 65.
• the linear actuator 65 When energized by the circuit board assembly machine control system, the linear actuator 65 will adopt the configuration shown, with the filter retracted from the optical axis of the camera 20.
• the linear actuator 65 When de-energized by the control system, the linear actuator 65 will adopt the configuration shown in Figure 4 of the drawing, with the linkage extended and the filter 61 deployed in front of the lens 30 of camera 20.
• the action of the actuator 65 will be the opposite of that described above: when the actuator 65 is energized, the filter 61 will be deployed and when the actuator 65 is de-energized, the filter 61 will be retracted. While the above description discusses the use of a linear actuator to deploy filter 61, it should be understood that a solenoid could also be employed in an embodiment of the invention.
• Filter 61 in Figures 3 and 4 could be the linear polarization filter 28 shown in Figure 1, employed in combination with linearly polarized illumination, as described above, to correct the visualization problem associated with metallic physical features on a light colored background.
• filter 61 could be one of several other types of filter chosen to correct other characteristic problems, as will now be described. These other types of filters can be used to equal effectiveness with polarized or non-polarized illumination.
• filter 61 could be chosen to be a red color filter. Such a filter would pass the red light reflecting from the red physical features while blocking the green light reflecting from the background, causing the physical features to appear substantially white and the background to appear substantially black in the image from a monochrome camera.
• camera 20 employs a charge coupled device (CCD) to form the electronic image
• CCD charge coupled device
• items that are especially reflective in the infrared spectrum may present a different characteristic visualization problem.
• a CCD is very sensitive to radiation in the infrared spectrum
• the electronic image of such an item may be washed out, with both the physical features and the background of the item appearing as light gray objects in the image, preventing the computer vision system from being able to recognize the physical features on the item.
• filter 61 could be chosen to be an infrared filter, which blocks infrared radiation and passes visible light.
• filter 61 could be chosen to be a circular polarizing filter. Such a filter restricts the rotation component of the illumination reflected from the item, thereby reducing glare from the item and allowing correct recognition of the physical features on the item. While the preceding discussion has described recognizing contacts on electronic parts or fiducials and contact pads on printed circuit boards and cards, it should be understood that the physical features being recognized on other items may not be contacts or fiducials.
• thermoset adhesive glue dots serve to mount parts that are not soldered to the board.
• FIG. 5 An embodiment of the invention allowing one of several filters to be deployed is illustrated in Figure 5 of the drawing.
• a rotational filter deployment apparatus 70 is shown, which is a filter wheel 75 mounted on the shaft of stepper motor 76. Also visible in Figure 5 are filters 61 and 63 mounted on the filter wheel 75 in registration with apertures 72 and 74.
• stepper motor 76 In response to signals from the assembly machine control system, stepper motor 76 will rotate to a specified position, thereby deploying the appropriate filter for the part being visualized.
• Filter wheel 75 can be seen to have, in this embodiment of the invention, four apertures 71, 72, 73, and 74. Apertures 72, 73, and 74 are covered by filters 61, 62, and 63, respectively, while aperture 71 is not covered with a filter.
• the hub of filter wheel 75 is mounted to the shaft of stepper motor 76.
• Lens 30 is seen through aperture 74. While motor 76 is described above as a stepper motor, it should be understood that servo motors could also be used in an embodiment of the invention to position filter wheel 75 in response to signals from the assembly machine control system.
• Figures 3, 4 and 5 show embodiments of the invention being used for visualization of a BGA package, it should be appreciated that the techniques of the invention can be used to improve visualization of other types of packages and of printed circuit boards and cards.

Landscapes

• Engineering & Computer Science (AREA)
• Operations Research (AREA)
• Manufacturing & Machinery (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
• Image Input (AREA)
• Image Processing (AREA)

Applications Claiming Priority (5)

Publications (1)

Family

ID=26698868

Family Applications (1)

Country Status (4)

Families Citing this family (5)

Family Cites Families (3)

• 2002
  • 2002-09-30 WO PCT/IB2002/004046 patent/WO2003032705A1/en not_active Application Discontinuation
  • 2002-09-30 EP EP02772667A patent/EP1438883A1/de not_active Withdrawn
  • 2002-09-30 JP JP2003535520A patent/JP2005505942A/ja active Pending
  • 2002-09-30 CN CNA02819389XA patent/CN1561659A/zh active Pending

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events