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Thermal Management of LED Lighting with Altair ProductDesign Support
Keywords: Topology Optimization, Thermal Management
LEDs suffer heat problems limiting their
success as a light source. To improve
the heat characteristics of LEDs much
attention is given to the heatsink, less to
the layers and barriers between LED and
the heat dissipating surface. A change of
concept and material, as carried out in a
consulting project by Altair ProductDesign
for CermTec AG shows how significant
gains in thermal management and
reliability as well as a simplified system
can be reached. As shown in the consulting
project, using ceramics as heatsink, circuit
carrier and part of the product design
opens the chance to overcome traditional
patterns.
A simulation process based on
Computational Fluid Dynamics supports
thermal optimization and technical product
design. Within the following case study we
will show how the new theoretical approach
works, validate the concept and describe
how improvements with ceramic heatsinks
can be achieved.
The Impact of HeatLEDs are known to be efficient and are
loved for being tiny. But they are only really
tiny as long as heat management is not
involved. Incandescent light sources work
with temperatures up to 2.500°C. LEDs are
much colder. Being relatively cold LEDs still
do produce heat since they are based on
semiconductors which, roughly speaking,
simply allow temperatures below 100°C.
According to physics the thermal energy
must be transferred to the surrounding area.
IndustryElectronics
ChallengeExplore the potential of using ceramics to improve the thermal management of LEDs
Altair SolutionOptimized ceramic heatsink developed which took manufacturing and cost requirements into account
Benefits• Highly effective heat management• Innovation new LED design
Key Highlights
Success Story
“The Altair ProductDesign department supported us in developing new innovative concepts for LEDs . We could not have been as successful as we were without their consultance.”
Dr. Alexander Dohn, CeramTec
The LED can only use a small temperature
gap between 100°C of the hot spot and
25°C ambience temperature; offering just
75 Kelvin. Consequently a larger surface and
powerful thermal management are needed.
Options for Improvement Before a new thermal management concept
was defined, the current solutions were
investigated. Group 1 is the LED itself and
mainly remains untouchable. Its centre is
a die and a heat slug, a copper part, which
connects the die with the bottom of the
LED. Thermally, the ideal solution is direct
bonding of the die to the heatsink itself.
Due to mass production, the LED has to be
considered as a standardized “catalogue”
product. Group 2 is the heatsink,
transmitting energy from a heat source to a
heat drain. This is usually the surrounding
air either with free or forced convection.
In-between group one and two is Group 3
providing mechanical connection, electrical
isolation and thermal transmittance. That
seems contradictory since most materials
with good thermal conductivity conduct as
well electricity.
Vice versa almost every electrical isolation
material translates into a thermal barrier.
The best compromise is soldering the LED to
a PCB which is glued on the metal heatsink.
The original function of a PCB as a circuit
board can be kept. Although PCBs exist with
various thermal conductivities they remain
an obstacle to thermal transfer.
New Material - New ConceptsThe ceramic heatsink CeramCool® is an
effective combination of circuit board and
heatsink for the reliable cooling of thermally
sensitive components and circuits. It enables
the direct and permanent connection of
components. Also, ceramic is electrically
insulating per se and can provide bonding
surfaces by using metallization pads.
Customer specific conductor track structures
can be provided, if required even three-
dimensional. The heatsink becomes a
module substrate that can be densely
populated with LEDs and other components.
Fig 1. Three groups build a thermal management system and are examined for optimization potential
It quickly dissipates the generated heat
without creating any barriers.
New Material - New ConceptsThe idea to use ceramics was first cross-
checked in several simulation models. To
predict thermal behaviour of various designs
a process based on Computational Fluid
Dynamics (CFD) was developed. Equally an
optimized ceramic heatsink for 4W cooling
was developed. Manufacturing requirements
where taken into account. The optimized
geometry allows operation of a 4W LED
at a maximum temperature below 60°C
which was validated against physical tests.
The design is square in shape (38mm x
38mm x 24mm) and comprises longer,
thinner fins with a larger spacing.
The identical geometry in aluminum with a
PCB mounted LED showed significant higher
temperatures. Depending on the thermal
conductivity of the PCB (from λ = 4W/mK to
1,5W/mK) the temperature rose between
6K to 28K. Already a 6K reduction at the hot
spot implies significantly less stress for the
LED.
New Material - New ConceptsSince most of the applications where
CeramCool® is used are customer
specific solutions, it is essential that the
performance can be proved before first
expensive prototypes are made. Intensive
studies were made to build up simulation
models. These simulation models have been
verified against various tests and showed
reliable correlations to test results. It’s the
designers choice whether he runs a LED on
its optimum temperature assuring high life
time and high lumen per Watt or he accepts
higher temperatures reducing life time and
efficiency.
A temperature spread from 50°C to 110°C
is common. If more lumens are needed the
4W heatsink can be equipped with 5W or
6W LEDs. Splitting the power into several 1W
LEDs helps to get a better heat spreading.
The results are 65°C with 5W and 70°C
with 6W.
Cooling Water at 1,5mm DistanceIn case simulation shows that air cooling
reaches its limits liquid cooling is best
suited. One example is CeramCool® water
cooling which benefits from the inertness
of ceramics. The concept follows the same
goal as for air cooled heatsinks: Shortest
(thermal) distance between heat source and
heat drain. With ceramic it is feasible that
cooling water is only 1,5 mm away from the
LED heat slug.
ConclusionAs shown, the developed CFD environment
for thermal management concepts enables
new concepts based on the newly developed
ceramic materials. Numerous advantages
over conventional design and materials
could be pointed out. Several comparisons
against tests underline the reliability of the
CAE-based development process.
With over a century of developmental experience and production expertise, CeramTec is a global leader in the field of production and supply of advanced ceramics and engineers these materials for use in a wide variety of applications.
About CeramTec
Fig 2. For validation purposes a simulation model has been developed.
Fig 3. Splitting the power for better heat spreading offers new prospects
Find out more about Altair ProductDesign at:www.altairproductdesign.com
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Altair Engineering, Inc., World Headquarters: 1820 E. Big Beaver Rd., Troy, MI 48083-2031 USAPhone: +1.248.614.2400 • Fax: +1.248.614.2411 • www.altair.com • info@altair.com
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Success Stories
Altair empowers client innovation and decision-making through technology that optimizes the analysis, management and visualization of business and engineering information. Privately held with more than 1,800 employees, Altair has offices throughout North America, South America, Europe and Asia/Pacific. With a 25-year-plus track record for innovative product design and development, advanced engineering software and grid computing technologies, Altair has more than 3,500 corporate clients representing the automotive, aerospace, government and defense, and consumer products verticals. Altair also has a growing client presence in the life sciences, financial services and energy markets.
Altair ProductDesign is a global, multi-disciplinary product development consultancy of more than 700 designers, engineers, scientists, and creative thinkers. As a wholly owned subsidiary of Altair Engineering Inc., this organization is best known for its market leadership in combining its engineering expertise with computer aided engineering (CAE) technology to deliver innovation and automate processes. Altair ProductDesign firmly advocates a user-centered, team-based design approach, and utilizes proprietary simulation and optimization technologies (such as Altair HyperWorks) to help clients bring innovative, profitable products to market on a tighter, more efficient time-scale.
HyperWorks is an enterprise simulation solution for rapid design exploration and decision-making. As one of the most comprehensive, open-architecture CAE solutions in the industry, HyperWorks includes best-in-class modeling, analysis, visualization and data management solutions for linear, nonlinear, structural optimization, fluid-structure interaction, and multi-body dynamics applications.
About Altair
www.altairproductdesign.com
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