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Electronics inspection system builder ups performance with FPGAs

Japanese inspection system builder, MEK Marantz Electronics, has been able to increase the resolution of its PCB inspection machines with FPGA processing.

MEK has integrated Silicon Software’s LightBridge external image processing device into its automated optical inspection systems, allowing the main camera’s total resolution to be raised from 2 to 4 megapixels.

The inspection system processes images from a total of nine 24-bit colour cameras: a 4 megapixel main camera with a 60fps image rate, and eight surrounding side cameras. LightBridge synchronises image processing of the main and secondary cameras and sends results to the host PC.

For inspection, printed circuit boards are oriented in the system with millimetre precision based on two to four fiducial markers, inspecting more than 2,000 points within a few seconds. ‘Our customers no longer have to do elaborate programming in a short period of time because the inspection system compares the points with error-free sample boards,’ explained Henk Biemans, managing director of MEK Europe.

The system analyses SMT and THT components based on presence, type identification, polarity, offset, text, and colour, as well as solder joints using reflow, wave, and selective processes. 3D solder joints are measured with four-angle multi-colour illumination with a meniscus profiler using light reflection. In the system, synthetic image comparison as well as spectral analysis and greyscale verification run as measurement procedures via analysis of brightness, colour tone and saturation.

Image preprocessing, such as white balancing, noise suppression, and gamma correction takes place on the FPGA in LightBridge. In the actual image processing, colour corrections are performed first and foremost to replace inauthentic colours with high-quality ones. Following colour reconstruction using a Bayer filter, conversion of RGB into HSL colour space follows, and other colour filters are used thereafter.

The FPGA can be programmed using VisualApplets from Silicon Software with the aid of graphical data flow diagrams. ‘VisualApplets allows us to develop the needed image processing applications ourselves instead of being dependent on support as we were before. The entire system thus becomes an open platform upon which we can modify individual applications at any time and add new ones,’ explained Hideki Konishi, project leader at Marantz Electronics in Japan.

Following classification of mated image elements with the aid of the side cameras, the images are evaluated. The recordings from the main camera are displayed on a monitor in a zoomable overall view with marked errors, while the eight side cameras provide additional zoomed individual recordings of errors from different perspectives. Since all errors are represented in 3D close-ups, it is no longer necessary to manually inspect the circuit boards microscopically.

‘This system for Apple computers, built together with Silicon Software, delivers highly precise 3D images for inspecting components and solder joints on circuit boards. LightBridge offers higher performance and increases reliability at the same time with use of optical Thunderbolt cables, as well as the elimination of multicore copper cables. As a result, we were able to increase the main camera’s total resolution from 2 to 4 megapixels, enabling higher data throughput,’ Konishi emphasised.

In Japan, the MEK inspection system has already been modified and successfully delivered, and is expected to now be offered worldwide, at which point porting onto further inspection systems will follow in the future.

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