AIA: Optical Inspection Speeds PCB Testing

Cirtronics Corp. uses an automated optical inspection system from Mirtec.

When Cirtronics Corp. (Milford, NH), a contract manufacturer of printed circuit boards, found that a new automated optical inspection (AOI) system would reduce its inspection times by a factor of 60, its interest was piqued. When the company further discovered that the system would keep pace with three of its pick-and-place machines, possibilities for process change were envisioned.

Manufactured by Mirtec (Suwon City, Kyunggi-Do, Korea), the desktop AOI system used by Cirtronics comprises a true-color camera system, LED lighting and motion control elements to position the camera relative to the board. A dedicated 1.5-gigahertz computer with a Pentium 4 central processing unit interfaces directly with the AOI unit via cable. Preloaded with software, it houses the AOI frame grabber and the system's optical character recognition algorithms.

"Cirtronics originally purchased Mirtec's desktop AOI system to perform first-piece inspections of surface mount components before reflow," says Christopher Lampron, surface mount process engineer at Cirtronics. "Prior to our addition of the Mirtec system, all inspection was performed manually, which is statistically only 30 percent effective. We inspected on an acceptable quality level basis at the machine, beginning with the first piece and every 25th piece after that."

It took 40 minutes to manually inspect a well-populated board to the bill of materials. But with the new AOI system, it takes only 40 seconds. The system also eliminates the 70 percent chance of human error. "Due to the speed of the machine, we have changed our process to include 100 percent inspection post-reflow. Even so, we have seen a substantial decrease in board returns that are surface-mount related," says Lampron.

The AOI system is programmed with a teach tool. The operator places a good board onto the workholder. Following instructions displayed via the system's user interface, the operator scans the board's image into the system. After the image is captured, the operator can then choose one of three ways to develop the inspection program.

Once the program has been generated, inspection can begin. The operator mounts the boards into the workholder and starts the process. Good boards are sent on to the next step in the assembly process. Boards that do not pass are reworked or discarded.

"Our ability to increase throughput by decreasing first-piece inspection time was an immediate benefit to implementing the desktop AOI system," says Lampron.

Because Cirtronics is pleased with the results of the AOI unit, it has purchased a second machine to inspect through-hole components. "In this application, we are using the unit as a process control tool to monitor the placement process and give the operators real-time feedback," says Lampron. Both systems paid for themselves within 6 months.

For more information on the automated optical inspection machines, call 011-82-31-202-5999 or visit

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