Application Note

Light Emitting Diode

Thermal Design Guide for the Nichia
NCSU334B (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 NCSU334B within this document is merely Nichia’s part number for this Nichia
product and is not related nor bears any resemblance to any other company’s product that might bear atrademark.
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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 theNCSU334B LED with high performance and high reliability, it is important to design the heat dissipation
so that the junction temperature (TJ) does not exceed the TJMAX of 110℃. Since the NCSU334B 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
configurations

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 NCSU334B are as follows:
NCSU334B
SymbolCondition
U280
TypMaxRθJS (℃/W)
8.4
9.9
VF (V)
IF=350mA
5.5
Absolute Maximum Ratings (TS=25℃):
IFMAX (mA)
IFPMAX (mA)
Topr (℃)
TJMAX (℃)

500600-10～85110

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 NoteThe measurement results for the above combinations are shown in the table below:
TA (℃)Part number

Wavelength Rank

25

NCSU334B

U280

IF (A)
0.35
0.50

VF (V)
5.3
5.4

W (W)
1.9
2.7

TS (℃)4452

TJ (℃)
6279

BoardThermal grease
Heatsink A

Light Emitting Diode

Picture 2. Evaluated light source 4-1-1
With heat dissipation configuration 4-1-1, there was enough margin to not exceed the TJMAX even when
0.50A was applied.
Nichia performed another evaluation 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
MaterialSize(mm)Al53 × 53 × t35

FinThickness of thebase Material(mm)4Number of finsSize(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

NCSU334B

U280

IF (A)
0.35
0.50

VF (V)
5.3
5.5

W (W)
1.9
2.8

TS (℃)3640

TJ (℃)
5467

Board
Thermal grease
Heatsink B
Picture 3. Evaluated light source 4-1-2
By increasing the size of the heatsink from A to B, the heat dissipation performance was improved andthe TJ was further lowered.

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Application Note
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
The specification of the board is as follows:
Copper foil

Thickness(mm)Insulation layer

Copper baseOutline dimensions(mm)

Internal circuit

LED mountingpitch (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)
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 (℃)Part number

Wavelength Rank

25

NCSU334B

U280

IF (A)
0.35
0.50

VF (V)
5.0
5.1

W (W)
1.8
2.6

TS (℃)77
88

TJ (℃)
94
113

BoardThermal 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 113℃ when 0.50A 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)385Thermal grease
Heatsink C
Fan

Picture 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

NCSU334B

U280

IF (A)
0.35
0.50

VF (V)
5.1
5.3

W (W)
1.8
2.7

TS (℃)3844

TJ (℃)
5670

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

25

NCSU334B

U280

IF (A)
0.35
0.50

VF (V)
5.2
5.3

W (W)
1.8
2.7TS (℃)
2931

TJ (℃)
4757

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 Note
Board
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).
When designing the system, pay attention to the orientation of the fins when installing the heatsink.

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

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）

Picture 10. TS measurement position of an LOB with nine LEDs
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Application Note
Heat dissipation configuration 4-2-1, nine LEDs on the board + Heatsink C
TA (℃)Part number

Wavelength Rank

25

NCSU334B

U280

IF (A)
0.35
0.50

TS measurement point
centeredge
centeredge

VF (V)
5.0
5.0
5.1
5.1

W (W)
1.8
1.8
2.6
2.6

TS (℃)
7758
8884

TJ (℃)
94
75
113
109

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.

Light Emitting Diode6. Summary
On a board with one LED, there was sufficient margin to stay under the TJMAX, even with an air-coolingheat dissipation configuration using only a heatsink. Additionally, a larger heatsink size resulted in aneven lower TJ.
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 NCSU334B 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
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http://www.nichia.co.jp

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