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How AOI Turned QC Around in Holland
Production floor at Electro-Watt in Holland shows an operator using a YTV B3 AOI benchtop system.
By Andy Bonner, Regional Manager, YESTech Europe, Alton, UK
Electronics manufacturers are naturally expected to deliver quality assured products, free of defects or returns issues. However they are also under increasing pressure to meet ever-shorter delivery times or respond to rapidly changing requirements. These demands can be hard to reconcile, and AOI systems with their inherently fast and flexible setups have long been heralded as a solution. In a recent review and installation, Hilversum (Netherlands) based electronics manufacturer Electro-Watt discovered just how far AOI systems have come in fulfilling this promise.
Electro-Watt has been delivering PC boards, wiring harnesses and complete electronics products into commercial and industrial markets for over 60 years. The company is increasingly asked to develop and deliver new products on a very short lead time — time frames that are simply insufficient to allow a testing strategy to be implemented. Under such circumstances, how can the company meet the delivery time while ensuring quality?
One way is for the customer to accept that the product has not been tested, and make allowances within his own incoming inspection and test procedures. Although workable, Electro-Watt does not see this as the best possible solution. The company would prefer more control and knowledge of the products it is shipping.
When the products in question are assembled PC boards, AOI technology becomes a potential solution. However, an original assessment performed by Electro-Watt many years ago did not convince management that they would achieve the depth of inspection with the throughput they wanted for an attractive price. By contrast, a more recent assessment satisfied them that significant technological advances had been made — enough to transform AOI into a valuable solution, now an integral part of the company's manufacturing and quality control process.
Electro-Watt's discovery of the "new" AOI is significant to all manufacturers who are not yet aware of AOI's updated potential. So what did Electro-Watt find that brought about the change of mind? And, after purchasing and installing an AOI system, what benefits have resulted?
AOI technology has evolved and improved due to two sets of factors. The first concerns developments within key system components and the second relates to how the industry has matured over the last decade or so.
AOI has always called for lighting, cameras and processing power. But in its early days, the lighting was incandescent or fluorescent, the cameras were heavy, expensive and analog, and PCs were slow and relatively costly. The software and user interface lacked intuitive ease of use and flexibility. None of this however deterred a large number of companies entering the market offering AOI products which could command a good sales price, even though they were relatively cheap to build. This resulted in a large number of systems that were expensive to purchase, and more troublesome than beneficial once they were installed.
Over time, however, these companies either disappeared or were absorbed into larger corporations who had the strength and commitment to drive AOI technology forward. Their efforts were facilitated by significant improvements and lower costs for all of the needed technology — lighting, camera and PC components that remained essential to AOI operation. Above all, major improvements and developments in software and user interfaces have resulted in machines that are faster and more intuitive to set up, and more quickly and easily reprogrammed for short-term production changes.
Evaluating AOI Systems
Electro-Watt evaluated different AOI suppliers' implementation of these developments through brochure comparison followed by production floor trials of the short-listed machines. YESTech's YTV-B3 benchtop product was selected, partly for its flexible user interface that allows for quick and easy programming, but also because of the support provided by YESTech — an element that Electro-Watt has continued to appreciate as the B3 has fulfilled its role within the manufacturer's production area.
Electro-Watt's PC board assembly area has two SMT production lines as well as through-hole production capability. The SMT operation has five on staff, and the B3 machine has been sited next to the SMT lines where it is used by the SMT line operator. This allows instant feedback in the event of manufacturing problems or defects.
AOI inspection is faster than functional or circuit testing, since it needs no knowledge of board or component behavior. Because of this, AOI provides the quality assurance Electro-Watt wanted without comprising its ability to meet demanding customer deadlines. And AOI's QA contribution comes from checking that every component location on a board is populated with the expected component, and that each component is correctly mounted and oriented with all leads reliably soldered. This checking can include plated-through holes and through-hole components, as a result of which the B3 can be used for an even wider range of products — an important consideration for Electro-Watt.
AOI success is maximized through complete inspection coverage with an extremely low false failure rate. The B3 is able to achieve this using its newly available Fusion Lighting
and advanced image processing technology. This integrates several techniques, including color, normalized correlation and rule-base algorithms.
The B3 is also flexible, which improves production throughput by facilitating different inspection levels. The operator usually chooses 100 percent inspection for a production run's first board and drops to a reduced inspection level for the rest of the run. When confidence is sufficiently well established, production can then continue in parallel with inspection, reducing to nil AOI's impact on throughput.
First Board Inspection
The 100 percent first board inspection is necessary to capture problems such as a wrong component reel on the pick-and-place machine, issues with the solder paste stencil screen, or oven temperature profiling. Checking for and eliminating any such problems on the first board obviates the need for the same level of inspection on the rest of the production batch. Instead, a reduced level of inspection captures instances of dropped parts or blocked stencil apertures. The AOI can revert to deeper inspection on, say, every 50th board if an event such as a component reel change on the pick-and-place machine is expected.
By being close in both process flow and physical location to the SMT lines, AOI can pick up faults very early, when they are still relatively easy to correct. Electro-Watt was amazed at how effective the AOI was in uncovering defects arising from a variety of causes. Early detection is commercially very significant; Electro-Watt estimates that costs increase by a factor of 10 for every manufacturing stage a fault passes through before detection. Equally importantly, this mode of detection allows the process to be improved continuously; future faults are prevented in the process of finding existing ones.
Electro-Watt manages its AOI strategy on a project-by-project basis. The company may, for example decide to perform 100 percent inspection on every 20th board, or on the first few boards produced, as experience and statistical analysis dictate. For a very small run of say five boards or less, they find it most efficient to inspect by overlaying the production board image onto that of a known good board.
Electro-Watt has been greatly encouraged by the experience since installing the B3. "We have seen a massive reduction in the number of defects that are detected in later manufacturing stages" commented Daan Terstegge, Operations Manager. "This owes much to AOI's process improvement role, preventing faults before they occur. The quality of the YESTech machine has been underscored by its favorable ratio of true-to-false defect reporting. And its inherent flexibility is greatly enhanced by the company's responsiveness to our software modification requests. Meanwhile, the pricing has now become acceptable, especially as the B3 is free of additional software license charges for the life of the machine."
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