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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 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 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
Over the next few years it is intended that COOLLED will role out a
number of innovative products based upon LED technology not just in
the UV spectrum, but across a wide spectrum of wavelengths and applications.
Each one of these products will address different applications in a
wide range of market sectors and will be distributed through a number
of companies who specialise in their respective areas/technologies.
A major investment
Nick Edwards, a director of CIL and technical 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.
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