LONDON A development programme led by Whitchurch-based Custom Interconnect Limited (CIL) has developed the COOLLED patent pending process that allows LED arrays to be produced in a high package density, increasing their suitability for industrial applications. CIL has now set up an independent company, using the COOLLED name to exploit the technology.
Nick Edwards, a director of CIL and managing director of COOLLED, said, “This two year research and development programme represents a major investment for the company. We are encouraged by the response of professionals working in the UV curing industry, our first target market.”
In 2002 the directors of CIL set out a company development programme with three aims: to develop the electronics contract manufacturing business; to increase the intellectual property of the company and develop its own products.
During 2002, LED array packaging was identified as an area of special interest and in January 2003 CIL set up a two-year collaborative research programme with the Optoelectronics Research Centre (ORC) at Southampton University. The ORC was established in 1989 by the Engineering and Physical Sciences Research Council (EPSRC). The Centre has extensive facilities including some of the best optical fibre and waveguide fabrication equipment in Europe, sophisticated laser and spectroscopy laboratories and a new clean-room complex occupying nearly 200sq m.
This brought together ORC’s experience in optical design and laboratory facilities and CIL’s knowledge of thermal structures and microelectronics assembly capability. The objects of the project were to investigate and characterise the existing methods of LED array manufacture and develop new methods that would enhance performance.
Despite improvements in light output in performance and the fact that LEDs are being used increasingly to replace incandescent lamps in many applications the problem facing designers is a balance of basic physics of increasing light output while dealing with the heat generated.
Although LEDs are three times as efficient as other light sources, only 15% to 20% of the energy is generated as light with the remainder being unwanted heat. The solution to this problem required a capability in bare semiconductor assembly and in-depth knowledge of thermal management.
An LED die typically measures between 0.3mm and 1mm square. Using modern production techniques, it is possible to mount the smallest of them at a density of 200 die/cm2. While this format creates high light output the real issue to be tackled is to maintain a low operating temperature of the die by effective thermal management.
The COOLLED research and development programme set about trying to harness this light output while managing the high levels of generated heat.
The solution was to create a micro reflector that captures the light emitting from the sides of the LED and throwing it forward to increase the effective light output. These reflectors are formed as thick copper ‘islands’ that are plated directly on to a ceramic substrate. As well as serving as optical reflectors they also act as heat spreaders to improve thermal transfer. The reverse side of this substrate was also plated with thick copper and bonded to the major heat sink.
Using this system it was established that the die density could be reduced and the light output increased for less generated heat. Extensive research has been carried out to determine the optimum cup size and shape. Once this was established, the optimum configuration proved to be a die density reduced from 200 die/cm2 to 120 die/cm2 that increased light output by 80% while reducing the generated heat flux by 40%.
This method of packaging that maintains cool operation of the LEDs, results in high power arrays that provide a significant step forward in terms of size and power density and formed the basis the COOLLED technology.
Initial products developed to exploit the COOLED technology include the 2600 LED UV curing pen, a hand-held device that produces bursts of high intensity UV visible light that is capable of light curing products within seconds, and a precision UV LED curing system, a desk top instrument that generates a flood of high intensity, single peak wavelength of UV light for the curing of inks, coatings and adhesives.
Jenton International has been appointed as the UK, European and USA distributor. Jenton represents some of the major suppliers of UV equipment in the UK market in addition to providing its own range of UV lamp systems.