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AOI and PCB Inspection

Active Silicon supports cutting edge PCB inspection

February 22, 2022

We’ve covered plenty of developments in technologies in our news stories, all requiring printed circuits boards (PCBs) to encompass more functions, offer more capacity, and be smarter. These advancements mean that the volume of PCBs in production has grown, and the number of solder joints, complexities and areas for inconsistencies in the boards have increased. The growth of surface mount technology and reduced board size further complicate manufacture. Faults in PCBs can lead to serious system failures in an end product, and include such diverse challenges as having insufficient or excess solder, missing components, parts being offset or damaged, or incorrect parts being fitted. Automated Optical Inspection (AOI) is a method of visually inspecting PCBs in order to detect imperfect boards, or identify them for removal from the production line and repair. Best employed after the solder step in board production to identify faults early in the manufacturing process, AOI is becoming a vital element of modern-day manufacturing and inspection.

System requirements
Implementing AOI is well suited to most industrial environments as light sources can be easily controlled and hardware does not need to be too rugged, allowing users to choose from a selection of components to build their systems. Systems can utilize one or more high definition cameras – of course, the more cameras used the more detailed the resulting image due to more angles being covered.  With components getting smaller, higher image resolutions are necessary while inspection is required to speed up. This all results in the need for faster imaging and we’re seeing an increasing number of manufacturers move to CoaXPress frame grabbers to meet the requirements of high-speed image acquisition. In addition, most modern production lines have the ability to capture 2D and 3D images, which can increase image processing time. High-speed image acquisition is again the solution to keep inspection time at the optimum level. Typically, images are acquired synchronized to the manufacturing line and lighting system – the lighting system being key by “strobing” in order to freeze the motion of the part, or the part is momentarily stopped and the camera triggered under continuous lighting.

Software running the image processing is also key. This must be able to analyze the PCB images at the rate of capture, and can be integrated into the camera(s) or run on a linked PC. Interestingly, some AOI providers, such as IVS and G2Metric, are implementing machine learning into their software which is allowing inspection machines to decide for themselves whether a previously unknown defect is critical or not.

Programming methods
Three variations of programming an AOI system prevail. The first one requires the pre-examination of a “golden” board – a perfect example that the system can then compare other boards to – and is known as template matching. Pattern matching refers to comparisons against good and bad examples that the system has already learnt. Statistical pattern matching is a little smarter and uses statistical methodologies to decide which deviations from the norm are acceptable, and which will result in rejection. Images and data about PCBs are programmed into the AOI system to educate it to know what to look for, and the system can be up and running quickly in a vast range of production lines.

AOI in action
Active Silicon Camera Link frame grabbers and CoaXPress frame grabbers are being used by several global players in industry-leading inspection systems. Our latest high-performance Firebird CoaXPress frame grabbers support CoaXPress v2.0, offering a fast PCI Express 4-lane and 8-lane Gen3 interface, zero CPU acquisition and can be used with cables of up to 35m at 12.5 Gbps, and over 100m at 3.125 Gbps. Firebird Camera Link frame grabbers support GenICam for Camera Link cameras, and maintain low latency even when used with multiple camera applications.

View our range of frame grabbers to see which one could enhance your inspection system and contact us for more information.