Application Note

Thermal Design Considerations for COB

Light Emitting Diode

LEDs - Selecting an Appropriate Heatsink

Table of contents
1. Overview .......................................................................................... 2
2. Evaluation Objectives .................................................................. 2
3. Evaluation Method....................................................................... 2
4. Evaluation Results......................................................................... 4
5. Summary....................................................................................... 10

The Nichia part numbers NTCxS024B-V1, NFCxL036B-V1, NFCxL060B-V1, NFCxJ108B-V1,
and NFDxJ130B-V1 within this document are merely Nichia’s part numbers for thoseNichia products and are not related nor bear resemblance to any other company’s
product that might bear a trademark.
This document contains tentative information, Nichia may change the contents without notice.
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Application Note
1. Overview

Light Emitting DiodeIn recent years, many luminaire designers have started to use COB LEDs in theirapplications and COB LED-based luminaires have become available on the market. Whendesigning a COB LED-based luminaire, one of the key requirements is to understand thethermal management of COB LEDs.
COB LEDs can produce high-power outputs and are designed to have multiple LED die
assembled close to each other in a single COB LED, causing heat to concentrate in a narrow
area. If COB LEDs become excessively hot during operation, it will cause the luminous flux
to decrease (i.e. temperature characteristics of COB LEDs) and/or shorten the lifetime. To
avoid the performance/reliability degradation, proper thermal management of COB LEDs
will be required, especially for the heatsink as it will play the primary role in dissipating theheat of the COB LED.
Nichia performed evaluations of heatsinks with an emphasis on the relationship between
the volume of a heatsink and the heat dissipation performance of the heatsink (i.e. junction
temperature of the COB LED). This application note provides information and data fromthe evaluations to select an appropriate heatsink for COB LEDs.

2. Evaluation Objectives
The evaluations were performed to determine:
1. the change in the junction temperature (TJ) depending on the volume of the heatsink
when the COB LEDs were operated in a constant current mode,
2. the heatsink volume required to ensure that the absolute maximum junction
temperature (TJMax) is not exceeded.

3. Evaluation Method
A COB LED was secured to an evaluation heatsink via COB LED holders and screws. Then,the assembly was installed in an enclosure1 with no ventilation and operated at thesorting/absolute maximum current of the COB LED (i.e. the constant current). Once thesaturation temperature at the junction had been reached, the temperature at the T C
measurement point (i.e. TC) was measured to calculate the TJ. For the part numbers andspecifications of the evaluated COB LEDs, refer to Table 1 below. For the evaluation
environment and the specifications of the assembly components except for the COB LEDs,
refer to Figure 1 below. For the position of the TC measurement point, refer to Figure 2
below.

Note:
1
Enclosure size (mm): L=350 x W=350 x H=350
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Application Note
Table 1. Specifications of the evaluated COB LEDs
IF [mA]

Light Emitting Diode

Part Number

Sorting Current

VF [V]
Max. Rating

Typ.

Current

NTCxS024B-V1

135

300

35.1

NFCxL036B-V1

260

540

35.0

NFCxL060B-V1

460

900

35.2

NFCxJ108B-V1

860

1620

35.3

NFDxJ130B-V1

1150

1800

39.2

TJMax [°C]140

密閉ボックス （無風空間）
Enclosure1 (with no ventilation)（350×350×350mm）

ホルダを用いてCOBをヒートシンクに固定。
COB LED secured to a heat sink
（放熱シート使用）
via holders2

ヒートシンク（Al5052）5052 aluminum-alloyHeatsink3
体積を変化させ、評価を実施。

Figure 1.

Evaluation environment

TC measurement point

Figure 2.

Position of the TC measurement point

Note:
2
Thermal film was used between the COB LED and the heatsink.
3
Different volumes of heatsinks were used
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Application Note
4. Evaluation Results
4.1 The NTCxS024B-V1 COB LEDs
4.1.1 Change in the TJ depending on the volume of the heatsink
Refer to Figure 3 for the change in the TJ vs. the volume of the heatsink when operated at:- IF = 135mA (i.e. the sorting current), which is equivalent to 5W- IF = 300mA (i.e. the absolute maximum rating current), which is equivalent to 11W

If the COB LEDs are operated at IF = 300mA, a heatsink with a volume more than 10cm3 isrequired to ensure that TJ does not exceed 140°C (i.e. TJMax).

NTCxS024B-V1 Volume of Heatsink vs. TJ

175

IF=300mA (equivalent to 11W)

150

IF=135mA (equivalent to 5W)

140°C (TJMax)

125

TJ [°C]Light Emitting Diode4.1.2 Minimum volume to ensure that the TJMax is not exceeded

100
75
50

TA=25°C

25
0

10

20

30

40

50

60

70

80

Volume of Heatsink [cm3]

Figure 3. Evaluation Result for the NTCxS024B-V1 COB LEDs

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Application Note
4.2. The NFCxL036B-V1 COB LEDs
4.2.1. Change in the TJ depending on the volume of the heatsink
Refer to Figure 4 for the change in the TJ vs. the volume of the heatsink when operated at:- IF = 260mA (i.e. the sorting current), which is equivalent to 9W- IF = 540mA (i.e. the absolute maximum rating current), which is equivalent to 20W
4.2.2. Minimum volume to ensure that the TJMax is not exceeded

NFCxL036B-V1 Volume of Heatsink vs. TJ

175

IF=540mA (equivalent to 20W)
140°C (TJMax)

150

IF=260mA (equivalent to 9W)

125

TJ [°C]Light Emitting DiodeIf the COB LEDs are operated at IF = 540mA, a heatsink with a volume more than 40cm3 isrequired to ensure that TJ does not exceed 140°C (i.e. TJMax).

100
75
50

TA=25°C

25
0

50

100

150

200

250

300

350

Volume of Heatsink [cm3]

Figure 4. Evaluation Result for the NFCxL036B-V1 COB LEDs

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Application Note
4.3 The NFCxL060B-V1 COB LEDs
4.3.1 Change in the TJ depending on the volume of the heatsink
Refer to Figure 5 for the change in the TJ vs. the volume of the heatsink when operated at:- IF = 460mA (i.e. the sorting current), which is equivalent to 16W- IF = 900mA (i.e. the absolute maximum rating current), which is equivalent to 33W
4.3.2 Minimum volume to ensure that the TJMax is not exceeded

NFCxL060B-V1 Volume of Heatsink vs. TJ

175

IF=900mA (equivalent to 33W)

150

140°C (TJMax)

IF=460mA (equivalent to 16W)

125

TJ [°C]Light Emitting DiodeIf the COB LEDs are operated at IF = 900mA, a heatsink with a volume more than 350cm3
is required to ensure that TJ does not exceed 140°C (i.e. TJMax).

100

75
50

TA=25°C

25

300

350

400

450

500

Volume of Heatsink [cm3]

Figure 5. Evaluation Result for the NFCxL060B-V1 COB LEDs

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Application Note
4.4 The NFCxJ108B-V1 COB LEDs
4.4.1 Change in the TJ depending on the volume of the heatsink
Refer to Figure 6 for the change in the TJ vs. the volume of the heatsink when operated at:- IF = 860mA (i.e. the sorting current), which is equivalent to 30W- IF = 1620mA (i.e. the absolute maximum rating current), which is equivalent to 57W
4.4.2 Minimum volume to ensure that the TJMax is not exceeded

NFCxJ108B-V1 Volume of Heatsink vs. TJ

175

IF=1620mA (equivalent to 57W)

150

140°C (TJMax)

IF=860mA (equivalent to 30W)

125

TJ [°C]Light Emitting DiodeIf the COB LEDs are operated at IF = 1620mA, a heatsink with a volume more than 400cm3
is required to ensure that TJ does not exceed 140°C (i.e. TJMax).

100
75
50
TA=25°C

25
300

400

500

600

700

800

900

Volume of Heatsink [cm3]

Figure 6. Evaluation Result for the NFCxJ108B-V1 COB LEDs

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Application Note
4.5 The NFDxJ130B-V1 COB LEDs
4.5.1 Change in the TJ depending on the volume of the heatsink
Refer to Figure 7 for the change in the TJ vs. the volume of the heatsink when operated at:- IF = 1150mA (i.e. the sorting current), which is equivalent to 45W- IF = 1800mA (i.e. the absolute maximum rating current), which is equivalent to 70W

As shown in Figure 7 below, when the COB LEDs were operated at IF = 1800mA, increasing
the volume of the heatsink did not have a significant effect on reducing the TJ. Since there
are cases where this approach is not effective, alternative solutions (e.g. use with coolingfans, heatsink with heat pipes, etc.) may be required to ensure that the TJ does not exceed
140°C (i.e. TJMax). The following section discusses the effectiveness of heatsinks with heat
pipes as a solution to the issue.

NFDxJ130B-V1 Volume of Heatsink vs. TJ

175

IF=1800mA (equivalent to 70W)
IF=1150mA (equivalent to 45W)

150

140°C (TJMax)

125

TJ [°C]Light Emitting Diode4.5.2 Minimum volume to ensure that the TJMax is not exceeded

100

75
50

TA=25°C

25
400

500

600

700

800

900

1000

1100

1200

1300

Volume of Heatsink [cm3]

Figure 7. Evaluation Result for the NFDxJ130B-V1 COB LEDs

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Application Note
4.6 Evaluation using a Heatsink with Heat Pipes
Nichia performed an evaluation to determine the effectiveness of heatsinks with heat pipes
in dissipating heat from the COB LED, especially in cases where increasing the volume ofthe heat sink is not sufficient (e.g. driving the NFDxJ130B-V1 COB LEDs at high wattages).
Refer to 4.6.1 for the evaluation method and conditions used and 4.6.2 for the results.

Light Emitting Diode4.6.1 Evaluation Method/Conditions
A COB LED was secured to a heatsink with heat pipes via a COB LED holder and screws.
Thermal grease was used between the COB LED and the heatsink. Then, the assembly was
installed in an enclosure with no ventilation and operated at the absolute maximum currentof the COB LED (i.e. the constant current). Once the saturation temperature at the junction
had been reached, the temperature at the TC measurement point (i.e. TC) was measured to
calculate the TJ.

LED Part No.
LED/Heatsink
Orientation
Cooling Method
Ambient Temp.
Heatsink with
Heat Pipes

HolderScrewsThermal Grease

NFDxJ130B-V1
See the image to the left.
Natural cooling (No ventilation
openings/gaps within the enclosure)25°C
HYC200 manufactured by Furukawa
Electric Co., Ltd.
143mm x 130mm x 220mm
Aluminum, Copper
Manufactured by TE Connectivity Ltd.
M3 pan-head screws tightened with atorque of 0.5N∙m (without washers)
SPG-30B manufactured by Fuji Polymer
Industries Co., Ltd.
Conductivity: 3.1W/m∙K

Figure 8. Conditions of the evaluation using a heatsink with heat pipes

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Application Note
4.6.2 Evaluation Results
As shown in Table 2 below, Nichia verified that when the NFDxJ130B-V1 COB LEDs wereoperated at the absolute maximum rating currents while being cooled by the heatsink withheat pipes, the TJ did not exceed the TJMax.
If these COB LEDs or similar/successor COB LEDs are designed into a high-wattage
application, determine the appropriate thermal solution (e.g. use with cooling fans,heatsink with heat pipes, etc.) for the application and perform a sufficient verification toensure that there are no issues with the thermal design since the COB LED can produce asignificant amount of heat.
Table 2. Specifications for the evaluated COB LEDs and evaluation results

Light Emitting Diode

Evaluation LED

IF [mA]

TJ4 [°C]

TJMax [°C]

114

140

1800mA
NFDxJ130B-V1(i.e. absolute maximum
rating current)

5. Summary
Since the volume of the heat sink has an effect on the TJ for COB LEDs, it is very importantto choose a heatsink of sufficient volume to improve the performance and the reliabilityof the chosen application.
To optimize the thermal design of the chosen application, it is critical to determine the T J
when the assembly/system and the COB LED are being operated. Since this T J can varydepending on the heatsink being used and Nichia COB LEDs have different thermal
resistances (i.e. RθJC), an actual measured TC should be used to calculate the TJ.
To maximize the heat dissipation for a chosen heatsink, the luminaire designer should also
consider how the COB LED is attached to the heatsink to ensure sufficient adhesion (e.g.
determining the correct tightening torque, thermal interface material [TIM], and theamount of the TIM, etc.). For more details, refer to Nichia’s application note entitled Heatdissipation performance according to the adhesion strength of COB and housing.

Note:
4
The TJ when the saturation temperature at the junction had been reached. These TJ are calculated values.
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Application Note

Light Emitting Diode

Disclaimer
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incorporated within it and Nichia makes no guarantee that customers will see the same
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http://www.nichia.co.jp

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