Application Note

Light Emitting Diode

Thermal Design Guide for the Nichia
NWSU333B (U365, U385) or
NWSU333B-D4 (U365) LEDs

Table of contents
1. Overview .......................................................................2
2. TJ Measurement Method ..............................................2
3. TS Measurement Point ..................................................3
4. Heat Dissipation Configuration and TJ Measurement
Results ...............................................................................3
5. Design Considerations ..................................................7
6. Summary .......................................................................8The Nichia part number NWSU333B and NWSU333B-D4 within this document is merely Nichia’s partnumber for these Nichia products and are not related nor bear any 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
The light output of LEDs decreases due to the effect of heat generation. When LEDs are operated above
the maximum LED junction temperature (TJMAX), the reliability will drop significantly. In order to use theNWSU333B and NWSU333B-D4 LED with high performance and high reliability, it is important todesign the heat dissipation so that the junction temperature (TJ) does not exceed the TJMAX of 100℃.
This application note covers the effect on the TJ when two types of mounted boards are driven withdifferent heat dissipation configurations.
・ TJ when one LED is mounted on the board and driven by two different heat dissipation configurations
・ TJ when nine LEDs are mounted on the board and driven by three different heat dissipation
configurations

Light Emitting Diode

2. TJ Measurement Method
The following equation can be used to calculate the TJ.
TJ = TS + RθJS × W
TJ: LED Junction Temperature (℃)
TS: Soldering Temperature (℃)
RθJS : Thermal Resistance from Junction to TS Measurement Point (℃/W)
W: Input Power (W) = IF(A)×VF(V)The specifications of the NWSU333B and NWSU333B-D4 are as follows:
SymbolCondition

RθJS (℃/W)
VF (V)

IF=3500mA

NWSU333B・NWSU333B-D4U365
TypMax
1.68
2.08
3.85
-

NWSU333B
U385
Typ
1.68
3.70

Max
2.08-

Absolute Maximum Ratings (TS=25℃):
IFMAX (mA)
IFPMAX (mA)
Topr (℃)
TJMAX (℃)

4500
6000
-10～85100

IF : Forward Current (mA)
IFP : Pulse Forward Current (mA)IFP conditions : pulse width ≤10ms and duty cycle ≤10%
Topr : Operating Temperature (℃)

Figure 1. TS vs Allowable Forward Current

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Application Note
3. TS Measurement Point
Cathode MarkAnodeTs Point

Cathode MarkAnode

CathodeFigure 2. TS Measurement point(NWSU333B)

Ts Point

CathodeFigure 3. TS Measurement point(NWSU333B-D4)

Light Emitting Diode

4. Heat Dissipation Configuration and TJ Measurement Results
The TJ was confirmed by changing the heat dissipation configuration when one LED was mounted on
the board and when nine LEDs were mounted.
4-1. TJ when one LED is mounted on the board and driven by two different heat dissipation
configurations
Heat dissipation configuration 4-1-1, One LED on the board + Heatsink A
The specification of the board is as follows:
Copper foil
0.105

Thickness(mm)Insulation layer
0.120

Outline dimensions(mm)30 × 30

Copper base
1.5

The thermal conductivity of the copper foil and copper base is 390W/m⋅K and that of the insulation layer
is 4.5W/m⋅K.

Figure 4. Structure of the board + LED

Picture 1. Board appearance Picture 2. Board appearance(NWSU333B)(NWSU333B-D4)

The specification of heatsink A is as follows:
Heatsink A
Material

Size(mm)

Al50 × 38 × t25

FinThickness of thebase Material(mm)
5

Number of fins

Size(mm)Arrangement8

1 × 388×1

Thermalresistance
(℃/W)
5.70

Thermal conductivity of thermal grease is 5.3W/m⋅K.

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Application Note
The measurement results for the above combinations are shown in the table below:
TA (℃)
25

Part number
NWSU333B
NWSU333B-D4

Wavelength Rank

NWSU333B

U385

U365

IF (A)
3.5
4.5
3.5
4.5

VF (V)
3.6
3.7
3.5
3.6

W (W)
12.6
16.7
12.3
16.2

TS (℃)
83101
75
90

TJ (℃)
109136100124

Board
Thermal grease
Heatsink A

Light Emitting DiodePicture 3. Evaluated light source 4-1-1 (NWSU333B)
With heat dissipation configuration 4-1-1 using the U385 rank, the TJ exceeded 100°C even when 3.5A
was applied, exceeding the TJMAX.
Since cooling is not possible with this heat dissipation configuration, Nichia performed anotherevaluation where the size of the heatsink was increased.

Heat dissipation configuration 4-1-2, One LED on the board + Heatsink B
The specification of heatsink B is as follows:
Heatsink B
Material

Size(mm)

Al53 × 53 × t35

FinThickness of thebase Material(mm)4Number of fins

Size(mm)Arrangement64

0.8 × 913 × 5

Thermalresistance
(℃/W)
4.25

Thermal conductivity of thermal grease is 5.3W/m⋅K.
The results of the evaluation with heatsink B are shown below:
TA (℃)
25Part number
NWSU333B
NWSU333B-D4

Wavelength Rank

NWSU333B

U385

U365

IF (A)
3.5
4.5
3.5
4.5

VF (V)
3.7
3.7
3.6
3.6

W (W)
13.0
16.7
12.6
16.2

TS (℃)
7387
6576

TJ (℃)
100
12291
110

Board
Thermal grease
Heatsink B
Picture 4. Evaluated light source 4-1-2 (NWSU333B)

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Application Note
In this heat dissipation configuration, when 3.5A was applied for the U385, the TJ was 91°C and did notexceed the TJMAX. When 3.5A was applied for the U365, the TJ was 100°C and exceeded the TJMAX.
100°C. However, by increasing the size of the heatsink from A to B, the heat dissipation performance wasimproved and the TJ was lowered.
If only one LED is used or if the LEDs are mounted with a wide enough pitch, it may be possible todesign a product that does not exceed the TJMAX by simply increasing the size of the heatsink.

4-2. TJ when nine LEDs are mounted on the board and driven by three different heat dissipation
configurations
Heat dissipation configuration 4-2-1, nine LEDs on the board + Heatsink C

Light Emitting DiodeThe specification of the board is as follows:
Copper foil
thickness(mm)

Insulation layer
thickness(mm)

Copper basethickness(mm)

Outlinedimensions(mm)

Internal circuit

LED mountingpitch
(mm)

0.035

0.120

1.560 × 60

3 series,
3 parallel

8.2The thermal conductivity of the copper foil and copper base is 390W/m⋅K and that of the insulation layer
is 4.5W/m⋅K.
TS measurement point (center)

Picture 5. Board appearance(NWSU333B)

Figure 5. Structure of the board + LED

Picture 6. Board appearance(NWSU333B-D4)

The specification of heatsink C is as follows:
Heatsink C
Material

Size(mm)Al

100 × 100 × t40

FinThickness of thebase Material(mm)7

Number offins
625

Size
Arrangement(mm)2×2Thermal resistance
(℃/W)
0.52

25 × 25

Thermal conductivity of thermal grease is 5.3W/m⋅K.
The measurement results for the above combinations are shown in the table below:
TA (℃)
25

Part number
NWSU333B

Wavelength Rank
U385

IF (A)
3.5

VF (V)
3.4

W (W)
11.9

TS (℃)146

TJ (℃)
171

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Application Note
In this heat dissipation configuration, the TJMAX was significantly exceeded even when 3.5A was applied
to the U385. The higher the current value and the shorter the wavelength, the more severe the heatdissipation.
When mounting LEDs with high density, the temperature rise is too large to be cooled by the heatsinkalone, Nichia performed another evaluation using forced air cooling with a fan.

Board
Thermal grease
Heatsink C

Light Emitting Diode

Picture 7. Evaluated light source 4-2-1 (NWSU333B)

Heat dissipation configuration 4-2-2, nine LEDs on the board + Heatsink with fan (heatsink Cwith fan attached)Board

The specification of the fan is as follows:Size(mm)
92 × 92 × t38

Fan
Volume flow(m3/min)
5.05

Thermal grease

Static pressure(Pa)385

Heatsink CFanPicture 8. Evaluated light source 4-2-2 (NWSU333B)

The measurement results of the heat dissipation configuration 4-2-1 with a fan attached are shown below:
TA (℃)
25

Part number
NWSU333B
NWSU333B-D4

Wavelength Rank

NWSU333B

U385

U365

IF (A)
3.5
4.5
3.5
4.5

VF (V)
3.7
3.7
3.6
3.6

W (W)
13.0
16.7
12.6
16.2

TS (℃)
5566
5056

TJ (℃)
82
1017690

In this heat dissipation configuration, the TJMAX was exceeded only when 4.5A was applied for U365. Byattaching a fan, the heat dissipation was improved significantly. For U365, the heatsink size should beincreased or the pitch width should be widened a little more to provide adequate cooling.

Heat dissipation configuration 4-2-3, nine LEDs on the board + Water-cooled Heatsink
The specification of the water-cooled heatsink is as follows:
Material
CuHeatsink
Size (mm)120 × 120 × t25

Water temperature(℃)
25

Water flow rate
(L/min)
5.6

Thermal resistance
(℃/W)
0.01

Thermal conductivity of thermal grease is 5.3W/m⋅K.
This document contains tentative information, Nichia may change the contents without notice.
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Application Note
The measurement results of the board + water-cooled heatsink shown in Picture 9 are shown below:
TA (℃)
25

Part number
NWSU333B
NWSU333B-D4

Wavelength Rank

NWSU333B

U385

U365

IF (A)
3.5
4.5
3.5
4.5

VF (V)
3.7
3.8
3.6
3.7

W (W)
13.0
17.1
12.6
16.7

TS (℃)
3944
3539

TJ (℃)
6680
6174

In this heat dissipation configuration, using the U365 rank, there was enough margin to not exceed theTJMAX even when 4.5A was applied. For the U365, water-cooling is recommended since even forced aircooling with a fan may not be sufficient.

Light Emitting DiodeBoard
Thermal grease
Water-cooled heatsink
Picture 9. Evaluated light source 4-2-3 (NWSU333B)

5. Design Considerations
5-1. Heat Dissipation Performance Depends on the Heatsink Orientation
The performance of naturally air-cooled heatsinks varies depending on the orientation of the fins of theheatsink. Since the TS will increase when warm air accumulates, it is important that the air movement isnot obstructed. At Nichia, the fins are placed to face vertically to allow warm air to escape from the top(See Figure 6).
When designing the system, pay attention to the orientation of the fins when installing the heatsink.

Picture 11.
Picture 10.
Fins facing down
Fins facing vertical(Nichia uses this orientation) (This orientation obstructs the air flow)

Figure 6.
Image of the heat path when finsare facing vertical

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Application Note
5-2. Heat Dissipation Performance Depends on the Mounted Position when Multiple LEDs areUsed
When multiple LEDs are mounted, the TS varies depending on the mounting pitch and position. As anexample, Nichia compared the TS and TJ between the center and the edge of the LEDs when nine LEDs
were mounted in heat dissipation configuration 4-2-2. The results are shown below.
TS measurement point（edge）
TS measurement point（center）

Light Emitting Diode

Picture 12. TS measurement position of an LOB with nine LEDs
Heat dissipation configuration 4-2-2, nine LEDs on the board + Heatsink with fan (heatsink Cwith fan attached)
TA (℃)Part number

Wavelength Rank

25

NWSU333B
NWSU333B-D4U365

IF (A)
3.5
4.5

TS measurement pointcenteredge
centeredge

VF (V)
3.7
3.7
3.7
3.7

W (W)
13.0
13.0
16.7
16.7

TS (℃)
55
47
66
55

TJ (℃)
82
74
101
90

According to these results, the TJ is about 10°C lower for the LEDs at the edges than for the LEDs in thecenter. Therefore, the LED in the center position should be used to measure the TS for the thermal design
since that is where the TJ is the highest.

6. Summary
When mounting multiple LEDs with high density, it is difficult to keep the LEDs within the TJMAX limit
with only a heatsink; however, if a sufficient pitch width is used, a fan is attached to the heatsink, or ifwater cooling is used, it is possible to keep the LEDs within the TJMAX limit. For high density
configurations, heat interference occurs between adjacent LEDs, resulting in poor heat dissipation,
making it necessary to use a sufficient pitch width or use forced air or water cooling. An appropriate
method should be selected after sufficient verification.
The absolute maximum ratings for the NWSU333B and NWSU333B-D4 LED per the Nichia
specification:
IF=4.5A, TJMAX=100℃
Nichia will not guarantee the LEDs if used above these ratings.

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Application Note

Light Emitting DiodeDisclaimer
This application note is a controlled document of Nichia Corporation (Nichia) published to provide
technical information/data for reference purposes only. By using this application note, the user agrees tothe following: This application note has been prepared solely for reference on the subject matters incorporated
within it and Nichia makes no guarantee that customers will see the same results for their chosenapplication.
 The information/data contained herein are only typical examples of performances and/or applications
for the product. Nichia does not provide any guarantees or grant any license under or immunity fromany intellectual property rights or other rights held by Nichia or third parties.
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http://www.nichia.co.jp

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