Print finer and straighter tracks on to a plastic substrate

25th March 2014

Nat Bowers

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Rainbow Technology Systems has a unique imaging process which enables finer and straighter tracks (down to below 20µm) to be printed on to a clear plastic substrate. “Retaining walls” are produced using a plating resist within which the seed layer is coated. The electroless copper grows within the straight walls of the resist, resulting in taller and much straighter tracks. In fact straight wall tracks up to 30 or 40µm can be produced. In principal the Rainbow process could produce multi-layered boards and eliminate the need to drill via holes.

As demand for curved TV screens, more sophisticated touchscreens and flexible smart phones continues to explode, Rainbow Technology Systems is at the forefront of developments in plastic electronics.

In traditional PCB production the copper is removed using a subtractive process whereas with additive chemistry a seeding layer is printed and electroless copper grows over the printed track. However the copper has a tendency to grow up and over the seed layer, which means tracks are not 100% bound to the substrate and are only bonded where the seed layer sits. This leads to poor adhesion of the electroless copper plate to the substrate.

Rainbow can also be used as a subtractive process using sputtered copper on a clear plastic substrate to create a conductive touchscreen. The Rainbow process can print very fine resist lines (down to below 10µm) and these lines are invisible to the human eye. The finer detail means the touchscreen can potentially process much more data more accurately than with current touchscreen capability. This will enable designers to incorporate greater functionality and make the screens more responsive to touch and even hand gestures. The closer together the high-density tracks can be placed the greater the amount of data the touchscreen can process.

At the Printed Electronics show, 1-2 April in Berlin, Rainbow will be demonstrating its revolutionary Desktop unit which incorporates coating, laminating and imaging in a compact unit. The system has been designed specifically for laboratory R&D prototyping and small-scale circuit board production making it suitable for designers to experiment with new circuits and configurations. Competitively priced, the unit offers a very cost-effective solution for laboratories and universities who want to create circuit prototypes without investing in conventional PCB production equipment.

The Rainbow Desktop Coater is suited for the creation of 18x12” sized single sided circuit boards, or with additional equipment double sided boards. The copper panel is clamped in place on the bed; liquid resist is then applied followed by immediate automatic lamination with a phototool and the panel is cured using a UV LED light bar mounted on the automatic carriage. Apart from creating printed circuit boards, the unit can also be used in many other applications where a precision coating has to be applied to a substrate.

Jonathan Kennett, CEO, Rainbow Technology Systems, comments: “We have employed much of the ground-breaking technology developed for the Rainbow Process Unit in the desktop machine. The unit is capable of producing very fine line circuitry at levels of 20µm and better, and is perfect for use in the fast emerging field of plastic electronics where there is a high demand for circuits which are flexible and can be produced in many different shapes and forms for a wide variety of applications.”