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

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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.

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