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COOLLED an innovative a new technology and a new company within the CIL group

Following an intensive, two-year research programme at CIL we have developed a new technology known as COOLLED, a patent pending process that allows Light Emitting Diodes / LED arrays to be produced in a high package density thus increasing their suitability for industrial applications. A new company, COOLLED Limited, has been formed within the CIL group to exploit the many commercial possibilities for this exciting new technology.

COOLLED - a new method of packaging LED arrays

In January 2003 we set up at CIL a two-year collaborative research programme with the Optoelectronics Research Centre at Southampton University, one of the world's leading organisations on the subject. This brought together ORC's experience in optical design and laboratory facilities and our in-depth 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.

The potential and problems associated with LED technology

LED performance is increasing dramatically each year with higher light output covering a broader range of wavelengths. Despite this improvement 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 LED's 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 highly developed capability in bare semiconductor assembly and in-depth knowledge of thermal management: skills and experience that CIL already possessed.

Harnessing the power

High power LED arrays that produce a high level of light output are becoming available commercially but the issue of thermal management still drastically restricts their application.

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 winning cup

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. This formed the basis the COOLLED patent pending technology.

Applying the new technology

When photopolymer materials were first used as an alternative to solvent based adhesives, mercury lamps were the only UV light source capable of activating the photopolymer.

Since then other bulb based lamps and microwave sources have been used but they all have a number of disadvantages. They are expensive to operate, have a wasteful warm up period, deteriorate rapidly and have a comparatively short life. In the case of lamp based devices this is only around 500 hours. They also produce a light source that has a wide spectral bandwidth with only 5% of the light produced being used for curing.

LED light sources on the other hand have a low cost of ownership, produce an immediate and consistent light source over a long period with a lifetime of over 10,000 hours. They produce a light with an extremely narrow bandwidth and offer the flexibility that multiple peaks can be introduced if required. It is also possible to flood three-dimensional areas with UV light for curing complex shapes. They are also significantly more efficient, need no maintenance and use no consumables. In addition, they do not contain mercury and they operate from a low voltage supply.

Two new UV curing products

Two new LED UV curing products have been developed by COOLLED.

COOLLED 2600 LED UV curing pen

This is a lightweight, hand-held device that produces bursts of high intensity UV visible light that is capable of light curing products within seconds.

COOLLED precision UV LED curing system

This is 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.

Route to market

Jenton International has been appointed as the UK, European and USA distributor. Jenton represents some of the leading names in UV equipment in the UK market in addition to providing its own range of UV lamp systems. It is a company that works in many markets and is committed to UV innovation and international marketing. www.jentonuv.co.uk

A major investment

Nick Edwards, a director of CIL and managing director of COOLLED, says: "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. We are convinced that COOLLED has real commercial viability and will become a significant part of CIL's business.

For more information visit www.coolled.com.



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