2011

Vision System Finds and Aligns Electronic Components

Nordson Asymtek, headquartered in Carlsbad, CA, provides automated fluid dispensing systems, which are used in the assembly and packaging of semiconductors, printed circuit boards, flat panel displays, electronic components, and medical/biotech products. The dispensing system, however, requires machine vision alignment tools so that components can be easily located. For processes like underfill, which secures a flip chip to the substrate circuit board, and encapsulation, where a chip must be protected from corrosion, precision is essential.

altNordson Asymtek began incorporating imaging technology from DALSA Corp., a Waterloo, Ontario, Canada-based digital imaging and semiconductor company, in 1995, and has since expanded its vision system and cameras to Nordson Asymtek’s Axiom, Spectrum, Select Coat®, and DispenseMate® dispensing tools.

To determine the precise location of workpieces and automatically correct workpiece misalignment, Nordson Asymtek incorporates DALSA's vision system components; including cameras, image processors, and Sapera machine vision software. A DALSA Genie M640 camera acquires an image of the part and, using a gray-scale correlation vision algorithm, locates the workpiece position. The vision system then guides a fluid-dispensing head to the specific location on the workpiece where it should operate.

A printed circuit board, for example, may feature small circular pads that are used for reference points, usually called “fiducials.” The camera will identify those pads to determine the orientation of the board after it enters Nordson Asymtek’s fluid-dispensing machine.

When the fluid-dispensing program is created, the engineer can also define the workpiece edges as fiducials. In production, the vision system captures an image of each workpiece after it is loaded in the machine, and determines both the corner location (where the two workpiece edges cross) and the angle of those two sides.

The vision system compares the measured workpiece locations with the locations specified when the fluid-dispensing program was created. It then calculates the exact distance that the fluid dispenser has to move, and the angle that it has to rotate, so that the fluid is placed on the part precisely where the engineer intended.

When the dispensing machine is initially set up, or after maintenance has been performed, Nordson Asymtek’s DispenseJet® ejects a “reference” dot onto a sample workpiece. The vision system then automatically identifies the center of that dot to establish the offset from the camera to the dispensing apparatus. This provides automatic calibration for the vision system and fluid dispenser.

Previously, Nordson Asymtek used a DALSA frame grabber and an analog camera, but now the company has put the DALSA Genie M640 camera to work. Nordson Asymtek has also developed software that synchronizes its motion controller with the camera to snap images at a precise moment in time. As the robotic system passes through pre-programmed locations determined through encoder feedback, the motion controller sends a signal to the DALSA Genie gigabit Ethernet camera to snap an image. Simultaneously the camera generates a signal to a Nordson Asymtek-designed strobe light to illuminate the image.

“We used to move to a target, stop the machine, wait for some vibrations to settle, snap an image, and process it,” said Ron Abernathy, principal engineer at Nordson Asymtek. “Now we move continuously over all of the programmed images without stopping. Processing of the images is done while in motion as well, so total fiducial finding time is significantly reduced.”

This month Nordson Asymtek intends to use Sapera processing software to find 2D bar codes so that specific customers have manufacturing traceability of their product as it goes through the fluid-dispensing machine. Previously, when this function was needed, a separate bar code reader from another manufacturer was used in the machine, increasing expenses and limiting bandwidth. That ca-
pability is currently being added within the DALSA vision system.

Cameras’ speeds, cost, and resolution have improved, which suggests that partnerships like DALSA and Nordson Asymtek are quite practical, if not essential, and cameras have become a standard feature on electronics manufacturing equipment.

For more details about DALSA’s Genie M640 camera, visit http://info.hotims.com/34452-153. For more information on Nordson Asymtek products, visit http://info.hotims.com/34452-154.

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