Application Note

Light Emitting Diode

Thermal Design Considerations for the
Nichia NCSxE17A Discrete Color LEDs

Table of Contents
1. Overview ............................................................................... 2
2. Applicable Part Numbers ....................................................... 2
3. Thermal Design ..................................................................... 3
4. Thermal Resistance................................................................ 7
5. LED Junction Temperature .................................................. 12
6. Thermal Evaluations ............................................................ 15
7. Summary.............................................................................. 20

The Nichia part numbers NCSRE17A, NCSGE17A, NCSBE17A, NCSCE17A, NCSAE17A,
NCSWE17A, and NCSxE17A 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 thatmight bear a trademark.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
1/21
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Application Note
1. Overview
Thermal design is very important for LEDs since it determines the optical and electricalcharacteristics (e.g. luminous flux, forward voltage, etc.) of the LEDs and it even largely affects thereliability (lifetime) of the LEDs. When performing a thermal evaluation, customers must check
how high the junction temperature of the LED will be when the LED is operated in theconditions/environments in which the LED will actually be used.
This application note provides cautions/suggestions for the thermal design of the chosen application
using the Nichia NCSxE17A discrete color and white LEDs to ensure that the luminous flux
required for the chosen application is obtained.

Light Emitting Diode

2. Applicable Part Numbers
This application note applies to the Nichia discrete color and white LEDs (hereinafter referred toas “NCSxE17A LEDs”). See Table 1 below.
Table 1. Applicable Part Numbers and Descriptions
Part Number

Emitted Appearance1 Maximum Forward Maximum Junction Thermal Resistance
Color
Currrent
Temperature(typ., max)2

NCSRE17A

Red(With
Phosphor)

700mA

135˚C

0.5˚C/W, 1.0˚C/W

NCSRE17A

Brilliant Red(With
Phosphor)

700mA

135˚C

0.5˚C/W, 1.0˚C/W

NCSGE17A

Green
(With
Phosphor)

550mA

135˚C

0.5˚C/W, 1.0˚C/W

NCSGE17A

Lime
(With
Phosphor)

700mA

135˚C

0.5˚C/W, 1.0˚C/WRoyal BlueNCSCE17A (Without
Phosphor)

700mA

135˚C

0.5˚C/W, 1.0˚C/W

NCSBE17A

Blue(Without
Phosphor)

700mA

135˚C

0.8˚C/W, 1.6˚C/W

NCSAE17A

Amber
(With
Phosphor)

700mA

135˚C

0.5˚C/W, 1.0˚C/W

NCSWE17A

White
(With
Phosphor)

700mA

135˚C

0.5˚C/W, 1.0˚C/WThis document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
2/21
Jun. 3, 2024

Application Note1
2

Outline dimensions for all LEDs listed above (NCSxE17A LEDs): 1.7mm × 1.7mm
The thermal resistance (RθJC) represents the resistance value from the LED chip to the LED
electrode.

Since the chip of the NCSBE17A LED has different characteristics from those of the other
NCSxE17A LEDs, the thermal resistance is higher than the other LEDs.

3. Thermal Design

Light Emitting Diode3.1 Thermal Resistance Model and Descriptions of the Terms
Figure 1 shows a cross-sectional view of a NCSxE17A LED mounted on an aluminum PCB withheat dissipation using a heatsink and Figure 2 shows a simplified thermal resistance model forthese LEDs.
TA: Ambient Temperature
TT: LED Surface Temperature
TJ: LED Junction Temperature

Distance: 2.35mm
TB: PCB Temperature

TC: LED Case TemperatureΦ1.0mmFigure 1. Cross-sectional View of a NCSxE17A LED
TT: LED Surface Temperature
RTJ: Thermal Resistance of the Phosphor Layer
TJ: LED Junction Temperature
RθJC: Thermal Resistance of the LED
TB: PCB Temperature

TC: LED Case Temperature

RP1:
PCB Thermal
Resistance 1

RP2: PCB Thermal Resistance 2
RC: Thermal Resistance of the Heat Dissipation Material
TA: Ambient Temperature

Figure 2. Simplified Thermal Resistance Model

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
3/21
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Application Note
Table 2. Terms, Descriptions, and Main Precautions
Term

SymbolLED Surface
Temperature

TT

Temperature of the emitting surface of the LED.

TJ

Temperature of the LED chip.
The maximum junction temperature of the NCSxE17A LEDs
is 135°C. To achieve longer reliability, ensure that the LEDs
are operated at a junction temperature of 100°C or less.

Thermal Resistanceof the LED

RθJC

Thermal resistance from the LED chip to the LED electrode of
the LED.
The RθJC is obtained according to the measurement/calculation
methods detailed in JESD 51-1 standard. The maximum
thermal resistance of the NCSxE17A LEDs is 1.6°C/W, which
is very low.

LED Case
TemperatureTC

Temperature of the electrode of the LED.
The TC is used in a thermal simulation; it cannot be measured
once the LED is soldered to the PCB.

TB

PCB surface temperature near the side of the LED package.
For the NCSxE17A LEDs, since it is difficult to measure thetemperature at the soldered area directly, the measurement
should be conducted at TB point shown in Figure 1.

RP1

Thermal resistance from the TC point of the LED to the TB
measurement point on the PCB.
The value of the RP1 varies depending on the soldering padpattern for the LEDs, the copper area and heat dissipation
performance of the aluminum PCB, heatsink, the operating
temperature, etc.

RθJB

Thermal resistance from the LED chip to the TB measurement
point on the PCB.
This thermal resistance value can be obtained by using thefollowing equation: RθJB = RθJC + RP1.

PCB Thermal
Resistance 2

RP2

Combined thermal resistance of an aluminum PCB in thevertical direction from the soldered area towards the heatsink.
The thermal resistance of an aluminum PCB varies
significantly depending on the properties of the insulating layer(thermal conductivity, thickness). Take this into consideration
when selecting materials.
The thermal resistance of an aluminum PCB can be obtainedby using the following equation:
Thermal resistance = Thickness of the insulating layer /(Thermal conductivity of the insulating layer × Its area)

Thermal Resistanceof Thermal
Dissipation Material

RC

Combined thermal resistance of a thermal sheet, thermal
grease, heatsink, etc.

Ambient
Temperature

TA

Ambient temperature of the LED assembled in the chosen
application.

Light Emitting Diode

LED Junction
Temperature

PCB Temperature

PCB Thermal
Resistance 1

Thermal Resistanceof from the LED to
the PCB

Description and Main Precautions

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
4/21
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Application Note
3.2 Materials for PCBs
Since the electrodes of the NCSxE17A LEDs are very small, the heat dissipation of the PCB used
is important. When the chosen application requires a large electric power, Nichia recommends using
an aluminum PCB with a high thermal conductivity instead of using a glass resin substrate (FR4),
a glass composite substrate (CEM3), or an aluminum PCB with a low thermal conductivity. For
reference, Figures 3 and 4 show the thermal simulations when an LED is mounted on aluminum
PCBs with low and high thermal conductivity.
TJ becomes high.

TJ becomes low.
Heat is dissipatedeasily.

Figure 3. Aluminum PCB witha Low Thermal Conductivity

Figure 4. Aluminum PCB witha High Thermal Conductivity

When an LED is mounted on an aluminum PCB with a low thermal conductivity, the heatdissipation becomes insufficient, resulting in a high junction temperature, whereas when an LED is
mounted on an aluminum PCB with a high thermal conductivity, the heat generated from the LED
can dissipate efficiently, resulting in a low junction temperature.
3.3 Recommended Soldering Pad PatternFigure 5 shows the recommended soldering pad pattern for the NCSxE17A LEDs. There are two
types of solder pad patterns: Solder Mask Defined (SMD) and Non-Solder Mask Defined (NSMD).
Table 3 provides the comparison between SMD and NSMD. Select a soldering pad pattern that is
appropriate for the chosen application.
(Unit: mm)

1.4
1.4
0.2
0.2

0.86
0.86

Light Emitting Diode

Heat is notdissipated easily.

Outlines of LED Package and the Electrodes
Soldering Pad Pattern ShapeFigure 5. Recommended Soldering Pad PatternThis document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
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Jun. 3, 2024

Application Note
Table 3. Comparison between SMD and NSMD
Solder Pad
Pattern

SMD

NSMD

Pattern
Design
MethodThe shape and location of thesoldering pad pattern are defined by
the aperture and location of the solder
resist.

The shape and location of the soldering
pad pattern are defined by the shape andlocation of the copper layer, not by thoseof the solder resist.

Light Emitting Diode

Appearance

Placement
Accuracy

Heat
Dissipation
Performance
Intended
PurposeCopper Layer

Copper Layer

Solder Resist

Solder Resist

If the coating accuracy of the solder
resist is poor, the shape and locationof the soldering pad pattern can differ
from the intended design dimensions(it may have effects on the placement
accuracy).

Even if the coating accuracy of the solder
resist is poor, the shape and location of
the soldering pad pattern will be the sameas the intended design dimensions (it may
have less of an effect on the placement
accuracy).

Good heat dissipation performance Limited heat dissipation performance due
due to a large copper layer area.
to a small copper layer area.
High heat dissipation performanceHigh density assembly

Nichia measured the thermal resistance values of the NCSxE17A LEDs using the following
parameters: the thermal conductivity rate of the insulating layer of an aluminum PCB and the lengthof the soldering pad pattern. The evaluation results are shown in Section 4.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
6/21
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Application Note
4. Thermal ResistanceNichia measured the thermal resistance (RθJB) of the NCSxE17A LEDs using the following
parameters: the thermal conductivity rate of the insulating layer of an aluminum PCB and the lengthof the soldering pad pattern. The RθJB was obtained in accordance with the measurement method
detailed in JESD 51-1 standard.
4.1 Evaluated LEDs

Light Emitting Diode

Table 4. Evaluated LEDs
Part Number

Emitted Color

Color Rank/
Color Rendering Index

Forward Current

NCSRE17A

Red

Rp

350mA, 700mA

NCSRE17A

Brilliant Red

R021

350mA, 700mA

NCSGE17A

Green

G013

350mA, 550mA

NCSGE17A

Lime

G014

350mA, 700mA

NCSCE17A

Royal Blue

V2

350mA, 700mA

NCSBE17A

Blue

W011

350mA, 700mA

NCSAE17A

Amber

Lea

350mA, 700mA

NCSWE17A

White

sm507, R70

350mA, 700mA

4.2 Specifications of the PCBs used for the Evaluations
Nichia used four different types of aluminum PCBs with insulating layers whose thermal
conductivity ranged from 1.8/m·K to 5.7/m·K. The specifications of the PCBs are shown in Table
5.
Table 5. Specifications of the PCBs
Aluminum PCB3

Unit

NRA-ES1

NRA-E
(3.0)

NRA-E
(6.5)

NRA-H6

Thermal Conductivity Rate of theInsulating Layer4

W/m·K

1.8

2.7

4.5

5.7

Thickness of the Insulting Layer

μm

120

120

120

120

Thickness of the Copper Layer5

μm

35

35

35

35

Thickness of the Aluminum Layer

mm

1

1

1

1

3

The aluminum PCBs are manufactured by NIPPON RIKA INDUSTRIES CORPORATION.
The thermal conductivities of the insulating layers are the values stated in the aluminum PCB
manufacture’s data sheet, these are not guaranteed values.
5
The thickness of the copper layer largely affects the heat dissipation performance. In theevaluations, the PCBs whose copper layer was a thickness of 35μm were used with considerationof the minimum clearance between the copper layers.
4This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
7/21
Jun. 3, 2024

Application Note
4.3 Length of the Soldering Pad Pattern
Nichia used PCBs with four different lengths: the minimum (0.5mm), the same as the electrodelength (0.86mm), the same as the length of the LED package (1.7mm), and the maximum (5mm).
Table 6. Soldering Pad Lengths
Length of Soldering
Pad Pattern

0.5mm

0.86mm

1.7mm

5mm

Solder Pad Pattern

NSMD

NSMD

SMD

SMD

4.4 Thermal Resistance Measurement Results
Figure 6 shows the thermal resistance (RθJB) of the LEDs on aluminum PCBs (thermal conductivityof the insulating layer: 1.8W/m·K) at IF=700mA6 with different lengths for the soldering pad pattern.

40

NCSRE17A: Red
NCSRE17A
Brilliant Red
NCSRE17A:
Brilliant Red
6
NCSGE17A
Green※6 GreenNCSGE17A:
NCSGE17A
Lime
NCSGE17A:
Lime
NCSCE17A
Royal BlueRoyal BlueNCSCE17A:
NCSBE17ABlue
NCSBE17A:Blue
NCSAE17A
Amber
NCSAE17A:
Amber
NCSWE17AWhiteNCSWE17A:White
NCSRE17A Red

35
30
RθJB(℃/W)

Light Emitting Diode

Pattern Image

25

20
15
10
6

5

The forward current of the NCSGE17A
Green LED: 550mA

00.5mm 0.86mm 1.7mm

5mm

Soldering Pad Lengths
Figure 6. Thermal Resistance (RθJB) of the NCSxE17A LEDs on Aluminum PCBs
(Thermal Conductivity of the Insulating Layer: 1.8W/m·K) at IF=700mA6This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
8/21
Jun. 3, 2024

Application Note
In this evaluation, the NCSRE17A LED (Red) showed the highest thermal resistance and the
NCSCE17A LED (Royal Blue) showed the lowest thermal resistance.
As the soldering pad pattern area becomes larger, the thermal resistance of the LEDs tends todecrease; thus, it is important to design the soldering pad pattern area as large as possible when
designing the PCB traces.
Figure 7 shows the thermal resistance (RθJB) of the LEDs on aluminum PCBs (thermal conductivityof the insulating layer: 5.7W/ m·K) at IF=700mA7 with different lengths for the soldering padpattern.
40

NCSRE17A: Red
NCSRE17A: Brilliant Red
NCSGE17A
Green※7 Green7
NCSGE17A:
NCSGE17A
Lime
NCSGE17A:
Lime
NCSCE17A
Royal BlueRoyal BlueNCSCE17A:
NCSBE17ABlue
NCSBE17A:Blue
NCSAE17A
Amber
NCSAE17A:
Amber
NCSWE17A:WhiteNCSWE17AWhite
NCSRE17A Red

NCSRE17A Brilliant Red

30

RθJB(℃/W)

Light Emitting Diode

35

25
20
15

10
7

5

The forward current of the NCSGE17A
Green LED: 550mA

00.5mm 0.86mm 1.7mm

5mm

Soldering Pad Lengths
Figure 7. Thermal Resistance (RθJB) of the NCSxE17A LEDs on Aluminum PCBs
(Thermal Conductivity of the Insulating Layer: 5.7W/m·K) at IF=700mA7
When the thermal conductivity of the insulating layer used in the aluminum PCBs was changed
from 1.8W/m·K to 5.7W/m·K, the thermal resistance of all the NCSxE17A LEDs decreased.
By comparing the thermal resistance values between Figures 6 and 7 at those different thermal
conductivities (1.8W/m·K and 5.7W/m·K), the difference in the thermal resistance due to thedifferent length of the soldering pad pattern with the thermal conductivity of 5.7W/m·K is smaller
than that with the thermal conductivity of 1.8W/m·K. This indicates that PCBs with a high thermal
conductivity are suitable to use when it is not possible to make the soldering pad pattern area larger.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
9/21
Jun. 3, 2024

Application Note
Table 7 provides the evaluation results of thermal resistance (RθJB) of the NCSxE17A LEDs under
different parameters.
LEDs on the Aluminum PCBs with an Insulating Layer
whose Thermal Conductivity is 1.8W/m・K
Length of theSoldering Pad Pattern

0.5mm 0.86mm 1.7mm

Forward Current

Light Emitting DiodeNCSRE17A Red

5mm

0.5mm 0.86mm 1.7mm

5mm

700mA
The current applied to
NCSGE17A Green LED is
550mA.
8

350mA
29.4

24.1

15.3

11.8

34.8

28.3

18.3

14.7

27.5

21.9

13.7

10.1

33.4

26.1

15.9

12.6

14.7

11.3

6.9

5.5

20.0

16.2

9.6

8.1

NCSBE17A Blue

22.9

17.0

10.0

9.2

26.3

19.8

11.5

10.0

NCSGE17A Green8

24.4

21.7

12.1

10.1

27.9

23.0

13.8

11.5

NCSGE17A Lime

24.0

18.6

12.7

10.7

26.9

20.2

13.4

11.2

NCSAE17A Amber

25.7

20.8

12.9

10.0

31.5

25.4

15.1

12.1

NCSWE17A White

20.2

17.1

10.1

8.9

23.5

19.2

12.0

10.2

NCSRE17A
Brilliant Red
NCSCE17A
Royal Blue

LEDs on the Aluminum PCBs with an Insulating Layer
whose Thermal Conductivity is 2.7W/m・K
Length of theSoldering Pad Pattern

0.5mm 0.86mm 1.7mm

Forward Current
NCSRE17A Red

5mm

0.5mm 0.86mm 1.7mm

5mm

700mA
The current applied to
NCSGE17A Green LED is
550mA.
9

350mA
26.0

20.5

13.4

10.8

29.1

23.8

15.3

12.4

23.8

19.9

12.1

10.3

28.0

23.0

14.5

12.3

11.5

10.0

8.0

5.7

15.6

13.2

9.1

6.7

NCSBE17A Blue

19.6

15.8

8.9

8.4

19.5

16.9

10.1

9.6

NCSGE17A Green9

22.3

18.4

12.0

9.6

24.8

20.8

12.9

10.6

NCSGE17A Lime

19.6

16.6

11.1

9.4

22.4

18.3

12.2

10.2

NCSAE17A Amber

24.4

19.6

11.7

10.8

26.8

22.0

13.4

11.4

NCSWE17A White

19.3

16.3

10.1

8.9

21.5

17.8

11.3

9.3

NCSRE17A
Brilliant Red
NCSCE17A
Royal Blue

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
10/21
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Application Note
LEDs on the Aluminum PCBs with an Insulating Layer
whose Thermal Conductivity is 4.5W/m・K
Length of theSoldering Pad Pattern

0.5mm 0.86mm 1.7mm

Forward Current
NCSRE17A Red

0.5mm 0.86mm 1.7mm

5mm

700mA
The current applied to
NCSGE17A Green LED is
550mA.
10

350mA
17.5

15.7

9.6

9.0

19.2

17.6

11.2

10.3

17.2

15.1

9.1

8.3

20.5

17.9

10.6

10.0

8.4

7.8

4.7

3.9

11.0

10.4

6.4

5.7

NCSBE17A Blue

16.1

13.2

8.7

7.9

15.7

13.5

9.0

8.1

NCSGE17A Green10

15.0

13.1

8.8

8.3

17.2

15.6

10.0

9.0

NCSGE17A Lime

14.8

13.3

8.8

7.6

16.6

14.6

9.7

8.8

NCSAE17A Amber

15.5

13.9

8.9

8.0

18.3

16.3

10.6

9.8

NCSWE17A White

14.2

11.7

8.0

6.3

15.1

13.3

8.9

8.6

NCSRE17A
Brilliant Red
NCSCE17A
Royal Blue

Light Emitting Diode

5mm

LEDs on the Aluminum PCBs with an Insulating Layer
whose Thermal Conductivity is 5.7W/m・K
Length of theSoldering Pad Pattern

0.5mm 0.86mm 1.7mm

Forward Current
NCSRE17A Red

5mm

0.5mm 0.86mm 1.7mm

5mm

700mA
The current applied to
NCSGE17A Green LED is
550mA.
11

350mA
15.1

13.2

8.3

7.7

16.8

14.2

9.8

9.4

13.5

11.8

8.3

7.3

16.1

14.2

10.2

8.9

7.4

6.5

4.7

4.8

9.8

8.2

5.7

5.7

NCSBE17A Blue

10.1

8.9

6.7

7.0

11.9

10.8

7.7

7.8

NCSGE17A Green11

12.5

11.6

7.5

6.3

13.7

12.9

8.4

8.0

NCSGE17A Lime

11.6

10.1

7.2

6.9

13.2

12.2

8.3

7.9

NCSAE17A Amber

13.4

10.9

8.4

6.7

14.6

12.2

10.2

8.6

NCSWE17A White

10.3

9.0

7.0

6.1

12.1

10.3

7.8

7.1

NCSRE17A
Brilliant Red
NCSCE17A
Royal Blue

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
11/21
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Application Note
5. LED Junction Temperature
5.1 How to Calculate the LED Junction Temperature
The junction temperature of the NCSxE17A LEDs is obtained by using Equation 1 below:
Equation 1: TJ = TB + RθJB × W

Light Emitting Diode

TJ: LED Junction Temperature (°C)
TB: PCB Temperature (°C)
RθJB: Thermal resistance from the LED chip to the TB measurement point (°C/W)
W: Input Power (IF × VF) (W)IF=Forward Current (A), VF=Forward Voltage (V)As explained in Section 4, the thermal resistance (RθJB) varies significantly depending on thespecifications of the aluminum PCB on which the LED is mounted.
For the thermal resistances required for calculating the approximate LED junction temperatures,refer to Table 7 in Section 4.
Note that the thermal resistance values detailed in this application note are ones obtained under
Nichia’s evaluation conditions and these values can differ depending on the other components usedin the chosen application, the operating condition, and the environment where the chosen
application is used.
If customers need help checking the thermal resistance of the LED on the PCB and the junction
temperature of the LED once it has been assembled in the chosen application, contact a local Nichia
sales representative.

5.2 LED Maximum Junction Temperature
The maximum junction temperature of the NCSxE17A LEDs is 135°C. To achieve longer reliability(to avoid a decrease in the luminous flux and significant color shift), ensure that the LED is operated
at a junction temperature of 100°C or less.
When the LED case temperature is high, a decrease in the bonding strength and solder cracks are
more likely to occur.
For reference, a “LED Case Temperature vs. Allowable Forward Current” graph provided in the“DERATING CHARACTERISTICS” section of the specifications for a NCSxE17A LED is shownin Figure 8. In Nichia’s specifications, the maximum case temperature is set as 100°C.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210113-4
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Application Note
The junction temperature of the NCSRE17A LED shown in Figure 8 is obtained by using Equation
2 below:
Equation 2: TJ = TC + RθJC × W
TJ: LED Junction Temperature (°C)
TC: Case Temperature (°C)
RθJC: Thermal resistance from the LED chip to the TC point (°C/W)
W: Input power [IF×VF] (W)When the case temperature of the NCSRE17A LED is 100°C, the LED junction temperature is
NCSxE17A
approx. 102.1 °C.
管理番号 No. STS-DA7-7695A
ケース温度測定部温度-許容順電流特性
Temperature at Measure Point on a Case vs
Example of NCSRE17A Red LED
Allowable Forward Current
Derating2

RθJA =15°C/W
RθJA =25°C/W
RθJA =35°C/W

1000(57, 700) (79, 700) (100, 700)

(100, 447)
(100, 319)

800

Allowable Forward Current(mA)

容順電流特性mperature vs
Forward Current
Derating1

許容順電流 Current (mA)
Allowable Forward

Light Emitting Diode

100°C+1.0°C/W × (0.7A×3V) = 102.1°C(100, 700)
600

400

200

0
0

20

40

60

80

100

120

周囲温度
Ambient Temperature(°C)

0

20

40

60

80

100

120

ケース温度測定部温度

LED Case Temperature (°C)

Temperature at Measure Point on a Case(°C)

Figure 8. LED Case Temperature vs. Allowable Forward Current-許容順電流特性
vsForward Current

0

5.3 PCB Temperature (TB) Measurement

Duty

T A =25°C

The appropriate sensor position for a thermocouple is as close as possible to the LED on the PCB.
Nichia recommends placing the temperature measurement point (diameter: 1.0mm) 2.35mm fromthe center of the LED. Nichia also recommends attaching the thermocouple to the PCB by solderingin a standard manner; however, when the PCB has an excellent heat dissipation performance, thesolder cannot melt which makes it difficult to attach the thermocouple by using solder.

0

In some cases, soldering the thermocouple is not possible for some light fixtures; for these cases,
the thermocouple should be attached by another method. Note that measurement errors occur withany thermocouple attachment method; sufficient evaluations must be done prior to use.
Table 8 provides examples of how thermocouples are attached to the PCBs for reference.

0
1

10
デューティー比Duty Ratio(%)

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Application Note
Table 8. Examples of How Thermocouples are Attached to PCBs
Attachment
MethodSoldering(Recommended)

Using Adhesive

Using Silicone Curing
Agent

Material Name Thread Solder: M705

Cemedine Super X2

Thermal Silicone

Composition

Sn-3.0Ag-0.5Cu

SVC-22

Manufacturer

Senju Metal Industry
Co., Ltd.

Acrylic-modified
silicone polymer
CEMEDINE Co., Ltd.
Apply the appropriate
amount of the adhesive.
(An excess amount ofadhesive may affect theamount of light emitted
from the LED, leading
to large measurement
errors from thethermocouple.)

Apply the appropriate
amount of the silicone
curing agent.
(An excess amount ofsilicone curing agent
may affect the amountof light emitted from the
LED and the heatdissipation performance,
leading to large
measurement errors
from the thermocouple.)

Light Emitting Diode

Appearance

Precaution

Avoid applying solder
flux to the emitting
surface of the LED.
(Adhesion to theemitting surface may
increase the LED
junction temperature.)

Sunhayato Corporation

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Application Note
6. Thermal Evaluations
Infrared thermography is an effective method to evaluate the temperatures of an LED-mounted PCB.
The LED junction temperature cannot be measured by infrared thermography; however, the LED
surface temperature and the temperature distribution over the entire surface of the PBC can beobtained by infrared thermography.
6.1 Examples of Thermal Evaluations of LED-mounted PCBs
Tables 9 and 10 show examples of the thermal evaluations for the four LEDs (Part No. NCSRE17A,
NCSGE17A, NCSCE17A, and NCSWE17A) arranged in a square on the PCB. In these evaluations,comparisons were made between LED-mounted PCBs with different PCB trace widths.

Light Emitting Diode

Table 9. Specifications of an LED-mounted PCB (NSMD)
LED-mounted PCB

LED Placement Configuration

Clearance between LEDs: 0.4mm
Outline of the Aluminum PCB:
Diameter: 140mm
Thickness: 1.0mm

12 NCSRE17A LEDs and 12 NCSGE17A LEDs

Insulating Layer:
Thermal Conductivity: 2.1W/m・K
Thickness: 120μm

12 NCSCE17A LEDs and 12 NCSWE17A LEDs

Copper Layer:
Thickness: 35μm

Circuit Configuration: 4 circuits (2 arrays connectedin parallel, each with 6 LEDs connected in series)

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Application Note
Table 10. Thermal Evaluation Results of the LED-mounted PCBs
PCB Trace
Width

0.4mm and 0.5mm (NSMD)

1.7mm (SMD)

X-ray Image of
the Circuit
Pattern

Light Emitting Diode

Temperature
Measurement by
Thermography
Measurement
Conditions:
Emissivity:
0.95
Reflection
Temperature:
20°C
Operated LEDs

NCSRE17A LEDs (discrete color)

NCSRE17A LEDs (discrete color)

Forward Current

350mA per LED

350mA per LED

LED Surface
Temperature

96.3°C (Average)

85.6°C (Average)

The surface temperature of the LEDs
on the NSMD pads is higher than thaton the SMD pads.

The surface temperature of theLEDs on the SMD pads is lower
than on the NSMD pads by 10.6°C.

Evaluation
Result

The temperauture of the PCB traces
connected between the LEDs is high.

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Application Note
6.2 LED Surface Temperature
Since the NCSRE17A, NCSGE17A, NCSAE17A, and NCSWE17A LEDs have a phosphor layer
above the LED chip, the LED surface temperature tends to be higher than the LED junction
temperature. Most of the heat is generated in the LED junction area; however, heat is also generated
in the phosphor layer due to the Stokes’ loss in the wavelength conversion. The phosphor layer ofthese LEDs is very thin and is located far from the heat dissipation path of the LED chip, leading
to the poor heat dissipation. Refer to Figure 9 for a schematic diagram of how the heat generated
flows within these LEDs.

Light Emitting DiodeLED Surface Temperature
Heat Generation Source: Phosphor Layer

Heat Generation in the Phosphor Layer: Even
though the heat is conducted via the LED chip, theheat cannot dissipate effectively.

LED Junction Temperature
Heat Generation Source: LED Junction
ThermalConduction

ThermalConduction

Figure 9. Heat Generation in the NCSRE17A, NCSGE17A, NCSAE17, and NCSWE17A LEDs

On the other hand, since the NCSCE17A and NCSBE17A LEDs do not have phosphor layers, thetemperature difference between the LED surface and the LED junction is not large. Refer to Figure
10 for a schematic diagram of how the heat generated flows within those LEDs.

LED Surface Temperature

LED Junction Temperature
Heat Generation Source: LED Junction
ThermalConduction

ThermalConduction

Figure 10. Heat Generation in the NCSCE17A and NCSBE17A LEDs

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Application Note
Figure 11 shows the temperature difference between the LED surface and the LED junction at
different forward currents.
50

NCSRE17A: Red
NCSR17A
Brilliant Red Brilliant Red
NCSRE17A:
NCSGE17AGreen
NCSGE17A:Green
NCSGE17A
Lime
NCSGE17A:
Lime
NCSCE17A
Roya Blue Royal BlueNCSCE17A:
NCSBE17ABlue
NCSBE17A:Blue
NCSAE17A
Amber
NCSAE17A:
Amber
NCSWE17AWhiteNCSWE17A:White
NCSRE17A Red

Difference in Surface andJunction Temperatures (°C)

Light Emitting Diode

45
40
35
30

25
20
15
10
5
0
350mA

550mA

700mA

Forward Current (mA)
Figure 11. Relationship between the LED Surface and Junction Temperature Differences
For the NCSRE17A, NCSGE17A, NCSAE17A, and NCSWE17A LEDs that have the phosphor
layer, the temperature difference between LED surface and the LED junction tends to become larger
as the forward current increases.
Whereas for the NCSCE17A and NCSBE17A LEDs that do not have the phosphor layer, thetemperature difference between LED surface and the LED junction is not large even when theforward current increases.
Note that the temperature difference between the LED surface and the LED junction shown in
Figure 11 is an evaluation result of the LEDs without optical components (e.g. lens or reflector).
The surface temperature of the LED assembled in a chosen application may increase due to otherfactors. The chosen application must be designed with sufficient margins to ensure the heat isdissipated properly.
6.3 Precautions for Thermography Measurement
Infrared thermography measurements will contain errors due to the measurement equipment,
measurement conditions, measurement environment, etc. When using measurement values obtained
through infrared thermography for the thermal design, the chosen application must be designedwith sufficient margins to ensure the heat is dissipated properly.
When using a close-up lens in the infrared thermography measurement, ensure that there issufficient distance between the close-up lens and the LED-mounted PCB. When performing thermal
measurements for LEDs with high light output, the measurement errors may be large due to effectsof the light emitted from the LED (see Table 11).
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Application Note
Nichia recommends that the LED surface temperature is 150°C12 or less. When the LED surface
temperature is high, it indicates that the LED has been operated under significant severe conditions;ensure that the PCB used, the shape of the soldering pad pattern, the performance of the heatsink,and the value of the forward current are appropriate for the chosen application.
Note that the LED surface temperature becomes even higher than the LED junction temperatureduring operation. When using optical components (e.g. lens or reflector) with a low heat resistancetemperature, ensure that the appropriate clearance is provided between the optical component andthe LED and that the heat resistance temperature of the optical component used must not be
exceeded.
Table 11. Evaluation Results at IF=700mA (NCSWE17A LEDs)

Light Emitting Diode

Lens TypeStandard Lens

Close-up Lens 1

Close-up Lens 2

Measurement
Distance

220mm

100mm

50mm

Magnification

2.0

1.4

1.0

LED Surface
Temperature

77.3°C

78.4°C

88.9°CPCB Temperature

37.4°C

37.6°C

40.9°C-The LED surface
temperatures and the
PCB temperature
increased due toreflected light(radiant heat).

Measurement
Environment

Thermography
Image

Note

-

12

For the NCSGE17A (color rank: G013) LED, Nichia recommends that the LED surface
temperature is 135ºC or less.

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Application Note
7. Summary

Light Emitting Diode

This application note explains important information and precautions for the thermal design of the
NCSxE17A LEDs. Select suitable PCB materials and thermal management materials for these
LEDs and perform sufficient thermal evaluations prior to use to ensure there are no issues for the
chosen application.

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Application Note

Light Emitting Diode

Disclaimer
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
to the 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 chosen
application.
 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 underor immunity from any 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, completenessor usefulness of any information contained herein. In addition, Nichia shall not be liable for any
damages or losses arising out of exploiting, using, or downloading or otherwise this document, or
any other acts associated with this document.
 The content of this application note may be changed without any prior or subsequent notice.
 Copyrights and all other rights regarding the content of this document are reserved by Nichia or
the right holders who have permitted Nichia to use the content. Without prior written consent of
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form or by any means, whether in whole or in part, including modifications or derivative works
hereof, is strictly prohibited.

491 Oka, Kaminaka-Cho, Anan-Shi,
TOKUSHIMA 774-8601, JAPAN
Phone: +81-884-22-2311 Fax: +81-884-21-0148

NICHIA CORPORATION
http://www.nichia.co.jp

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