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SMT & Inspection | December 13, 2005

Digitaltest adds soft landing<br> to its flying probes

Digitaltest GmbH has introduced 'Soft Landing' technology on the Condor flying probe test platform addressing concerns that manufacturers face over test coverage on complex and high density boards and the problems of unwanted damage using conventional probe techniques.
With increasing product miniaturization, driven largely by industries using high technology communications such as automotive, medical, and military applications, the increasing density of components has affected almost all areas of printed circuit board assembly. With the resulting limited space for test points and the placement of components on both sides of the board
flying probe systems have found new life.

However, despite their flexibility, flying probe systems still face a number of challenges. Passive component packages now vary from 0805 and 0603 to 0402 and 0201 in dimension. The adoption of smaller components creates smaller 'targets' for test nails. Component leads also tend to become thinner and consequently more delicate, easily damaged by the aggressive speeds and forces that test machines are required to work at in a time-critical production environment.

High density interconnect components (ICs, interconnects and connectors) also create test challenges, often having contact pads much smaller than required for test probe access. Many sections of modern surface mount technology (SMT) boards are no longer fully accessible by existing probe-contact test methods and require a new approach if they are to be fully tested.

Just as crucially, printed circuit boards (PCBs) have become more advanced and complex themselves, using new materials, shapes and sizes. New platings, including immersion gold on electro less nickel, immersion silver for lead free solder, immersion white tin and Entek with OSP finish (Organic Solderability Preservative) are becoming more common, since they offer
alternatives to hot air solder finish. However, these new plating types are sensitive when it comes to testing, since they are more easily scratched by test nails.

'Soft Landing' addresses these concerns in a unique and effective way. The principle is relatively simple: the test nail travels towards the component or pad at normal speed until approximately 1-2 mm above its target landing position. The speed of the nail is then reduced to soften its impact with
the board. This protects delicate components from damage and also minimizes the 'footprint' where the nail touches the board. In tests, adding a soft landing to an existing nail contact reduced the visible 'footprint' by more than a third.

A smaller footprint means more precise positioning in highly dense areas. It also lowers the chance of shorting leads that are in close proximity to each other, invalidating the test and creating another source of potential damage.

"Although it may sound like a simple idea, the 'Soft Landing' technique will have a sizeable impact of the effectiveness of flying probe systems in electronics production, especially in applications for highly complex boards," says Hans Baka, Managing Director of Digitaltest. "With the constant pressure to improve quality and yield, it could well be the step that revolutionizes the next generation of testing technologies."

With 'Soft Landing', test coverage increases as more test points can be reached without being damaged or scratched and that's good news for manufactures seeking higher test coverage from difficult boards. 'Soft Landing' only affects the Z-axis of travel which means that on the Digitaltest MTS systems existing test programs can be updated to take advantage of the soft landing technique with minimal additional programming.

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