Nigel Priest looks at the benefits of having both flying probe and automated optical inspection capability in a single platform and why there is a need for such a product.

A common dilemma for manufacturing companies presents itself when selecting new test equipment or technology. Frequently there are crossovers in capability between competitive products, but due to limited capital investment, manufacturers are also forced to decide what capability is needed most between different test techniques. As circuit boards become more complex the test strategy decision is becoming more and more important.
A single platform has now been developed which offers symbiotic testing using both flying probe and automated optical inspection (AOI) techniques, which helps to address some of these problems.
The issue of more components and less space is an area that has continued to grow in importance in the electronics manufacturing sector. As finished products become smaller with greater functionality the component density on circuit boards has increased, making it more difficult to test properly using conventional test techniques such as bed of nails in circuit test (ICT).
Reduction of costs both in capital expenditure in new equipment and the ongoing cost of producing and testing circuits are still areas that remain a high priority, as the manufacturing industry struggles to recover from the recession that it has faced over the past 18 months. Industry and national press continually report of more and more manufacturing contracts being outsourced to offshore locations, leaving UK-based manufacturing companies to fight for what is left. In short it remains a fiercely competitive environment.
As well as this, reduced product lifecycles and shorter time to market has also become an issue for manufacturers. If test strategies are implemented at board design stage, test engineers are able to work along side the designers. If faults can be predicted at this stage it will result in fewer design alterations, lower test costs and improved time to market, providing competitive advantage.

In response to these issues, as well as considering customers concerns and needs, SPEA (UK) Limited identified that it was necessary to approach the topic with fresh thinking, in order to provide the industry with a new solution. As traditional ICT becomes more and more redundant due to the fact that circuit boards are now more crowded, and even double sided, manufacturers need new and improved test strategies in order to effectively check what they are producing.
Both flying probe and AOI are preferred methods for testing, however the issue of choice is a problem, because they both provide benefits in different ways and it isn't always possible to invest in both types of equipment.
SPEA's solution is a flying probe hybrid test platform which expands on SPEA's existing 4040 Hi-Line flying probe product in order to give it AOI functionality. This provides benefits to users in a number of ways. Manufacturers no longer have to choose between investing in flying probe or AOI, as they can be afforded economical access to both methods. Once in possession of this single platform, they will be able to choose the most effective test method for the item that they are manufacturing, and can decide how much AOI or electrical testing to run. If AOI testing is run and there are failures, the platform can be adjusted and electrical testing can take place to see if there is failure in that area. It is also possible for optical and electrical tests to be performed simultaneously.

Flying probe test equipment is able to access hard to reach components on boards that conventional test equipment such as bed of nails can not access, therefore giving users a higher level of test coverage. If AOI capability is then added it means that the scope of testing is widened even further. Not only does this increase the coverage but it will also increase capacity as the test procedure has been reduced by a stage due to both flying probe and AOI tests being completed together. This means that an increased number of boards, and higher volumes can be tested in less time over a larger area, and it also allows for process validation and electrical testing all in one.
AOI capability will also provide the manufacturer with the flexibility of high mix/low volume manufacturing, as well as the option to measure and determine the accuracy of component placement automatically. This combined with reduced false defect identification can help to lower tool programming, and therefore costs.
While performing conventional flying probe tests the optical inspection module on the platform will also enable tests such as optical character recognition (OCR) for the verification of characters or prints on the board or components; part presence and part absence on the board; component orientation for parts such as polarized capacitances, connectors, integrated circuits and diodes; and manual verification of specific areas of the board for things such as rework of jumper settings.
The AOI function, as well as defining different brightness and contrast levels allows the manufacturer to choose between three different light sources. This means that the test system can adapt to various marking techniques used on components, which can in turn eliminate false failures caused by poor lighting.
The flying probe/AOI platform also has the scope to be expanded modularly into a larger platform - namely SPEA's high level process validation tool. SPEA anticipates that this single platform, with however many modules, will help to improve manufacturing process validation and cycle time as well as reducing both line bottlenecks and rework, whilst maximising coverage for manufacturers. Some of the modules that can be added include net impedance testing, power-on functional testing and device programming.

To summarise, combined flying probe and AOI will provide manufacturing companies with numerous benefits such as test access to components that could not be tested by conventional Bed of Nails and optical testing on components that cannot be tested electrically such as decoupling capacitors and characters on labels and devices.
The platform offers a single solution so that manufacturers can reduce the number of test stations it has on its premises, which will help to reduce the overall test time, due to the simultaneous testing capability that it offers.
Ultimately the customer can have the best of flying probe and AOI in one piece of equipment without having to make the choice between the two.
SPEA is continuing to develop functionality to add on to the base system of the product, which will be done by constant analysis of the market place, issues and customer feedback. The fact that the platform can be integrated with existing equipment means that it removes the need for the manufacturer to replace entire stocks of test equipment when purchasing something new. This provides even more economic options for manufacturers.

Nigel Priest is managing director of SPEA (UK) Limited, Slough, Berkshire, UK. www.spea.net