APPLICATION NOTE

LED Chip Heat
Dissipation Mapping
The LED chip is the core component ofLED lighting. If the chip temperature is
too high, the LED life and luminous quality
could be severely affected.

What is a heat sink andwhy is it important?
A heat sink is a common component in many electronic devices.
It transfers the heat created bya device, acting to reduce thedevice’s temperature to prevent
overheating. Heat sinks are an
important part of LED lighting,more specifically LED chips. Theheat sink aids in heat dissipation of the chip, ensuring thatthe temperature of these chips
stays within the appropriate
range. Testing heat sinks in theproduction process of LED chips
is critical to ensuring quality.
Infrared cameras can be used in
the R&D process to check LED
heat sinks. The readings from acamera can help manufacturers
find potential problems withmaterials and designs, to better
analyze and improve heat sinkquality.

Relationship between theLED chip temperature andthe heat sink
To continue operating properly, LED chip temperature
should not exceed 120 °C. Aschip temperature increases,
the unfortunate reality is that
service life decreases. So, if thechip temperature is very high,or even worse, exceeds 120 °C,
service life of the chip will beshortened.
Therefore it is important tostay below 120 °C to maintainchip performance and service
capability. This emphasizes theimportance of the heat sink—theheat sink is what cools the LED
chip. If the heat sink is unavailable, poorly designed, or madeof improper material, the heatdissipation effect will be seriously affected, thus shortening
the LED service life or resulting
in a change of LED color.

CASE:Figure 1

We worked with the R&D
department for a large LED manufacturer to understand how LED
chips are tested. The manufacturer stated the importance ofthe heat dissipation effect andheat sink size when designinga heat dissipation scheme forthe chip. Six types of heat sinks
were designed for research.
As shown in Figure 1, the heatsink area increases as you
move from bottom left to top
right. These figures have thesame chip under the same input
voltage, current and the samelighting time.
In Figure 2, the temperature
at the upper middle position is48.1 °C, inconsistent with thetemperature trend of heat sinksize. Normally the estimatedvalue should be in the range of
43 °C to 44 °C. Since we see inthe figure that the temperature
falls outside of this range, it islikely that the design or material selection of the heat sinkhere is flawed. The image canalso be used to calculate theheat dissipation per unit area by
focusing on the area size andFigure 2

temperature. In this example, itis clear that the design at theupper right corner has the worst
heat dissipation effect, and thelower left corner shows the bestheat dissipation effect.

What are the advantages ofthe infrared camera?

Before an infrared camera,
what was used to measure
the temperature during
heat dissipation R&D of anLED chip?
Before the introduction of infrared cameras, a thermocouple
was the most popular way tomeasure temperature during
heat dissipation.
In Figure 3A the LED chip(circular part) uses a strip-likeheat sink, and Fluke SmartView
desktop reporting and analysis software is used to perform
linear analysis for the temperature distribution at different
distances as seen in Figure 3B.

Metal bands
Figure 4A®

In Figure 4A there are metal
bands (purple color on the heat
Figure 4Bsink) segmented on the striplike heat sink. This is causing
the temperature of these segments to be low due to the lowemissivity. This is seen on thegraph (Figure 4B) where thetemperature drops down, highlighted by the black circles.
Figure 3A

What are the disadvantagesof using the thermocouple
for testing?

Figure 3B

The thermocouple has a few
limitations. The first disadvantage of using a thermocouple isthat it must make contact withthe surface to take a measurement. To be able to makecontact there must be a surface
placed over the heat sink using
glue which can alter the temperature reading. In addition
when using a thermocouple you
can only take a point measurement. This means that only asingular point of the heat sinkis tested which does not provide an accurate reading for thewhole heat sink.

2 Fluke Corporation LED Chip Heat Dissipation Detection

The infrared camera can quickly
test the performance of the radiation fin. The online monitoring
and real-time shooting thermal
map features can be used toconduct specific temperature
analysis of the fin on a PC. An
infrared camera is a non-contact
form of temperature measurement which decreases the time
it takes to measure the apparent
temperature and is more accurate. The temperature profile ofthe heat sink with other related
analysis functions is of major
importance to help optimize theheat sink design thus prolonging
the LED chip life.

When you are performing tests
make sure to keep accuracy asa priority. Here are three things
to keep in mind for better LED
inspections.
1. The metal material emissivity ofsome heat sinks leads to a low temperature reading. To avoid incorrect
measurements, apply silicone greaseor paint to the radiation fin.
2. Given the different sizes of various
LED heat sinks, an add-on macrolens can help provide more detailed
and accurate readings.
3. When using the camera for LED
inspections look down upon theitems being inspected and not froman angle.

See what you’re missing
Whether you’re designing the next mobiledevice, scaling down passenger vehicles,or developing a new stronger, lighter polymer,
make sure you have the best thermal data you
can get. For accurate and efficient R&D infrared
testing, we recommend the Fluke RSE series—
RSE300 and RSE600 Infrared Cameras. With
down to 40mK thermal sensitivity, and up to
640 x 480 resolution, these mounted cameras
stream data to your PC for R&D and quality
assurance analysis.
To find out more about how these versatile,
high resolution, high accuracy cameras
can help you develop better products faster,
consult your Fluke sales representative or
visit www.fluke.com/infrared for more
information.

Fluke. Keeping your worldup and running.®
Fluke CorporationPO Box 9090, Everett, WA 98206 U.S.A.
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PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:In the U.S.A. (800) 443-5853 or
Fax (425) 446-5116
In Europe/M-East/Africa +31 (0)40 267 5100 or
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In Canada (800)-36-FLUKE or
Fax (905) 890-6866
From other countries +1 (425) 446-5500 or
Fax +1 (425) 446-5116
Web access: http://www.fluke.com©2018 Fluke Corporation. All trademarks are theproperty of their respective owners. Data subject tochange without notice. 3/2018 6010582a-en
Modification of this document is not permitted
without written permission from Fluke Corporation.

3 Fluke Corporation LED Chip Heat Dissipation Detection