AOI: The best QA tool for highly responsive electronics production
Thursday, 14 May 2009 06:00
Automated Optical Inspection (AOI) has long been promoted as the right QA solution for fast moving, highly responsive electronics production environments. This article looks at how AOI technology has evolved to deliver on this promise.
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 setup have long been heralded as a solution. In a recent review and installation, Hilversum based electronics manufacturer Electro-Watt discovered just how far AOI systems have come in fulfilling this promise.
Electro-Watt has been delivering PCBs, wiring harnesses and complete electronics products into commercial and industrial markets for over 60 years. They are increasingly asked to develop and deliver new products on a very short lead time; insufficient to allow a testing strategy to be implemented. Under such circumstances, how can they 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 accordingly within his own incoming inspection and test procedures. Although workable, Electro-Watt does not see this as an optimum solution. They would prefer more control and knowledge of the products they are shipping.
When the products in question are assembled PCBs, AOI technology becomes a potential solution. However an original assessment performed by Electro-Watt many years ago did not convince them 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 which is now an integral part of their manufacturing and quality control process.
Electro-Watts discovery of the ‘new AOI is of significance to all manufacturers not yet aware of AOIs updated potential. So what did Electro-Watt find that changed their mind? And, after accordingly purchasing and installing an AOI system, what benefits are they actually enjoying?
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 analogue, and PCs were slow and relatively expensive. 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 while being relatively cheap to build. This resulted in a large number of systems that were expensive to purchase, and more troublesome than beneficial once installed.
Over time, however, these companies either disappeared or became 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 the lighting, camera and PC components that remained essential to AOI design. Above all, 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.
Electro-Watt evaluated different AOI suppliers implementation of these developments through brochure comparison followed by production floor trials of the shortlisted machines. They chose YesTechs YTV-B3 benchtop product partly for its flexible user interface that allows for quick and easy programming but also because of the support provided by YesTech Europe – an element that Electro-Watt has continued to appreciate as the B3 has fulfilled its role within their production area.
Electro-Watts PCB assembly area has two SMT production lines as well as through hole production capability. The SMT operation has five staff. 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 as it needs no knowledge of board or component behaviour. Because of this, AOI provides the quality assurance Electro-Watt sought without comprising their ability to meet demanding customer deadlines. And AOIs QA contribution comes from checking that every component location in a board is populated with the expected component, and that each component is correctly mounted and oriented with all leads reliably soldered. Checking can include plated through holes and through hole components, as a result of which the YesTech B3 can be used for an even wider range of products which is an important consideration for Electro-Watt.
AOI success is maximised through complete inspection coverage with an extremely low false failure rate. The YesTech B3 achieves this using its newly available Fusion Lighting and advanced image processing technology. This integrates several techniques, including colour, 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% inspection for a production runs 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 AOIs impact on throughput to nil.
The 100% 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. And 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 as well as existing ones detected.
Electro-Watt manages their AOI strategy on a project by project basis. They may, for example decide to perform 100% inspection on every 20th board, or on the first few boards produced, as experience and statistical analysis dictates. 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 their 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 at Electro-Watt, "This owes much to AOIs process improvement role, preventing faults before they occur. The quality of the YesTech machine has been underlined by its favourable ratio of true to false defect reporting. And its inherent flexibility is greatly enhanced by YesTech Europes responsiveness to our software modification requests. Meanwhile, the pricing has now become acceptable, especially as the B3 is free of additional software licence charges for the life of the machine."
About YESTech Europe
Since its inception, YESTech has been a consistent innovator in the electronic inspection industry. Founded and managed by a team of industry experts with a history of success, YESTech brings the most powerful, cost-effective yield enhancement solutions to the electronics market.
YESTech is represented in Europe by YESTech Europe. Based in Alton, Hampshire, with easy access to the UKs motorway, airport and seaport network, YESTech Europe offers fast and responsive local sales and technical support to electronics manufacturers across the region.