Application Note

Light Emitting Diode

Thermal Design Guide for the Nichia
NC4U334BR (U280) 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 NC4U334BR within this document is merely Nichia’s part number for thisNichia product and is not related nor bears any resemblance to any other company’s product that mightbear a trademark.
This document contains tentative information, Nichia may change the contents without notice.
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Application Note
1. Overview

Light Emitting DiodeThe 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 theNC4U334BR LED with high performance and high reliability, it is important to design the heatdissipation so that the junction temperature (TJ) does not exceed the TJMAX of 110℃. Since theNC4U334BR requires a high input power it generates a larger amount of heat.
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
configurations2. 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 NC4U334BR are as follows:
SymbolCondition

RθJS (℃/W)
VF (V)

IF=350mA

NC4U334BR
U280
TypMax
2.8
3.1
22.5
-

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

500
600-10～85
110

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 Mark
CathodeAnodeTs Point

Figure 2. TS Measurement point

4. Heat Dissipation Configuration and TJ Measurement Results

Light Emitting Diode

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

Copper base
1.5

Outline dimensions(mm)
30 × 30

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.

Picture 1. Board appearance

Figure 3. Structure of the board + LED

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

Size(mm)

Al50 × 38 × t25

FinThickness of thebase Material(mm)5Number of finsSize(mm)Arrangement

81 × 38

8×1

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 (℃)

Part number

Wavelength Rank

25

NC4U334BR

U280

IF (A)
0.35
0.50

VF (V)
20.6
21.0

TS (℃)
7087

W (W)
7.2
10.5

TJ (℃)
92
120

Board
Thermal greaseHeatsink A

Light Emitting Diode

Picture 2. Evaluated light source 4-1-1
When heatsink A was used, the TJ reached 120℃ when 0.50A 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 (℃)Part number

Wavelength Rank

25

NC4U334BR

U280

IF (A)
0.35
0.50

VF (V)
20.6
21.1

W (W)
7.2
10.6

TS (℃)6173

TJ (℃)
83106BoardThermal grease
Heatsink B

Picture 3. Evaluated light source 4-1-2
When heatsink B was used, the TJ reached 106℃ when 0.50A was applied and did not exceed the TJMAX.
This confirms that by increasing the size of the heatsink, it is possible to cool the system even in an
air-cooled environment.
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Application Note4-2. TJ when nine LEDs are mounted on the board and driven by three different heat dissipation
configurationsHeat dissipation configuration 4-2-1, nine LEDs on the board + Heatsink C
The specification of the board is as follows:
Copper foilThickness(mm)Insulation layer

Copper baseOutline dimensions(mm)

Internal circuit

LED mounting
pitch (mm)

0.035

0.120

1.5

60 × 60

3 series,
3 parallel

8.2

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.

Light Emitting DiodeTS measurement point (center)

Picture 4. Board appearance
and measurements points

Figure 4. Structure of the board + LED

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

Size(mm)

Al100 × 100 × t40

FinThickness of thebase Material(mm)7

Number offins
625

SizeArrangement
(mm)
2×2

Thermal resistance(℃/W)

25 × 25

0.52

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

Wavelength Rank

NC4U334BR

U280

IF (A)0.35

VF (V)
19.6

W (W)
6.9

TS (℃)137

TJ (℃)
158

Board
Thermal grease
Heatsink C

Picture 5. Evaluated light source 4-2-1
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Application Note
In this heat dissipation configuration, the TJ reached 158℃ when 0.35A was applied, exceeding theTJMAX.
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.

Heat dissipation configuration 4-2-2, nine LEDs on the board + Heatsink with fan (heatsink Cwith fan attached)
The specification of the fan is as follows:

Light Emitting DiodeSize(mm)92 × 92 × t38

Fan
Volume flow3(m /min)
5.05

Board
Static pressure(Pa)385

Thermal grease
Heatsink CFanPicture 6. Evaluated light source configuration, 4-2-2
The measurement results of the heat dissipation configuration 4-2-1 with a fan attached are shown
below:
TA (℃)Part number

Wavelength Rank

25

NC4U334BR

U280

IF (A)
0.35
0.50

VF (V)
20.5
21.0

W (W)
7.2
10.5

TS (℃)4958

TJ (℃)
7191

With this heat dissipation configuration, the TJMAX was not exceeded even when 0.50A was applied. By
attaching a fan, the heat dissipation is improved and cooling is possible.

Heat dissipation configuration 4-2-3, nine LEDs on the board + Water-cooled Heatsink
The specification of the water-cooled heatsink is as follows:Heatsink
MaterialSize (mm)Cu
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.
The measurement results of the board + water-cooled heatsink shown in Picture 7 are shown below:TA (℃)

Part number

Wavelength Rank

25NC4U334BR

U280

IF (A)
0.35
0.50

VF (V)
20.8
21.4

W (W)
7.3
10.7

TS (℃)3844

TJ (℃)
6177

Even with this heat dissipation configuration, when 0.50A was applied, it did not exceed the TJMAX of110℃. With water cooling, it can be adequately cooled.
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Application NoteBoard
Thermal grease
Water-cooled heatsink
Picture 7. Evaluated light source 4-2-3

Light Emitting Diode5. 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 is
not obstructed. At Nichia, the fins are placed to face vertically to allow warm air to escape from the top(See Figure 5).

Picture 9.
Picture 8.
Fins facing down
Fins facing vertical(Nichia uses this orientation) (This orientation obstructs the air flow)

Figure 5.
Image of the heat path when finsare facing vertical

As an example of the increase in the TS when the air flow is obstructed, the TJ was measured when thefins were facing vertical and when the fins were facing down. The following table shows themeasurement results verified with heatsink A.
TA (℃)Part number

Wavelength Rank

25

NC4U334BR

U280

Heatsink orientation
Fins vertical
Fins downward

IF (A)
0.35
0.50
0.35
0.50

VF (V)
20.6
21.0
20.5
20.9

W (W)
7.2
10.5
7.2
10.5

TS (℃)
7087
7897

TJ (℃)
92
120
100129Compared to the case where the fins are facing vertical, the TS is increased by about 10℃ when the finswere facing down.
When designing the system, pay attention to the orientation of the fins when installing the heatsink.

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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 10. 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

NC4U334BR

U280

IF (A)
0.35
0.50

TS measurement pointcenteredgecenteredge

VF (V)
20.5
20.621.0
21.1

W (W)
7.2
7.2
10.5
10.6

TS (℃)
49
46
58
57

TJ (℃)
71
68
91
90

According to these results, the TJ is slightly 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
If the number of mounted LEDs is one or if a sufficient pitch width is used, it may be possible to design
with only a heatsink without exceeding the TJMAX by increasing the heatsink size.
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 fan is attached to the heatsink or if water 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.
The absolute maximum ratings for the NC4U334BR LED per the Nichia specification:
IF=0.50A, TJMAX=110℃
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.
 Nichia makes no representation or warranty, express or implied, as to the accuracy, completeness or
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NICHIA CORPORATION
http://www.nichia.co.jp

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