Application Note

Light Emitting Diode

Thermal Design Considerations for PCBs
for the Nichia 170 or 131 Series LEDs

Table of Contents
1. Overview ........................................................... 2
2. Applicable LED Series ...................................... 2
3. Thermal design for metal-based PCB ............... 3
4. Thermal design for FR-4 ................................. 10
5. Summary ......................................................... 14

The Nichia part numbers NCSW170C and NCSW131C within this document are merely Nichia’spart numbers for those Nichia products and are not related nor bear resemblance to any othercompany’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 thermal management for the LEDs is managed by Junction Temperature (TJ). If TJ value is outof spec. as overheated, it brings negative influence on reliability and might occur No-light mode at
the worst case. Therefore, the thermal design is important such as not exceeding maximum TJ
defined in the specification.
The LEDs have such structures typically as radiating heat mainly from the package backside, and
the PCB is related and important factor to consider thermal management. This document introduces
thermal designs with some evaluated results including simulations.

This application note provides thermal design considerations for the Nichia 170 and 131 Series
LEDs.
In the evaluations provided herein, the NCSW170C and NCSW131C LEDs were used; refer to theevaluation results for the other part numbers included in the Nichia 170 and 131 Series LEDs.
Table 1. Evaluated Part Numbers
NCSW170C
1.45

NCSW131C
Unit:mm1.45(0.715)

Cathode(0.51)

1.8

1.15(0.51)

1.8

LED Outline Dimensions

Anode

0.3

0.815

of Back Side

Emitting area

0.3

1.6

Emitting area

Electrode Pattern

Unit:mm1.15(0.715)

1.15

1.15

Part Number

1.6

Light Emitting Diode

2. Applicable LED Series

0.3
1.23

1.23

Chip
Heatsink
Die Heat
Sink

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Application Note
3. Thermal design for metal-based PCB
The following items are introduced as the focused points for thermal design with metal-based PCB.
Area size and thickness of Cu layer
Thermal conductivity of insulating layer
Material of metal base
LED mounting pitch (clearance)

Generally, FR-4 is often used for LED mounting boards, but metal board PCB has the advantage oflower TJ controlled with its thermal management potential. The thermal designs with metal-based
PCB are introduced in the following sections.
Also, this document uses images (drawings) omitting the resist mask pattern in order to make easierto understand the Cu layer pattern when explaining thermal design. Actually, the resist mask isneeded in consideration of LED mountability, and the recommended land pattern for the resist mask
are shown in the specification sheets of each LED.
3.1 Area size and thickness of Cu layer
Area size and thickness of Cu layer are important factors when designing heat radiation of mounting
boards. The followings show the simulation results by changing area size and thickness of Cu layer.
LED Part No.:
Mounting board:
Heatsink:
Simulation soft:

NCSW170C (Forward current IF=1(A), Mounting LED 1 piece)
Al-based PCB (Size 40×40×1.5t(mm), Thickness of insulating layer 120(μm))
A6063 (Size 40×40×25t(mm))
Flotherm

TA=25(℃)

10090ThicknessofofCu
Cu layerlayer
Thickness
35(μm)
35[μm]

TJ[℃]
(℃)
Tj

Light Emitting Diode

A)
B)
C)
D)

70(μm)
70[μm]

80

105(μm)105[μm]

70

60
1

10

100

1000

2)
Area
size ofof Cu
Cu layerlayer(mm[mm2]Area size

Figure 1. TJ vs. Area size and thickness of Cu layer (Simulation result)This document contains tentative information, Nichia may change the contents without notice.
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Application Note
Table 2. Temperature distribution on Cu layer vs. Area size of Cu layer(Thickness of Cu layer 35(μm))
Area Size of
Cu Layer

Dimension of Cu Layer

Thermal Distribution
on Cu Layer

LED
Cu layer40
3.8531(mm2)

70℃

40
8

Board

60℃

LED
Cu layer40
7.85

125(mm2)

70℃

40
16

Board

60℃

50℃
LED
Cu layer
40

70℃

17.85

650(mm2)

Board
40
36

Light Emitting Diode

50℃

60℃

50℃

As Figure 1 shows, TJ can be lowered when the area size and thickness of Cu layer are bigger. Also,
as Table 2 shows, the heat dissipates radially which occurred from heat source, therefore the bigger
area size and thickness of Cu layer is effective design on heat radiation.

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Application Note
3.2 Thermal conductivity of insulating layer
The thermal conductivity of insulating layer is one of the important parameters on heat radiation of
metal-based PCB. Even if a metal-based PCB is used, when the lower thermal conductivity of
insulating layer, it might be same performance level as FR-4 at the heat radiation effect. There arevarious metal-based PCBs with 0.8(W/mK) for inexpensive one, and 10(W/mK) or more for
expensive one. Each manufacture of metal-based PCB uses a different insulating layer, and there areseveral grades in a manufacturer so that it needs to note when considering thermal designing.
LED Part No.:

Heatsink:
Simulation soft:

Clearance
0.3

40

Pitch
1.75

40

0.3

Figure 2. Evaluation PCB

Figure 3. Heatsink

TA=25(℃)

120
110

100

TJ [℃](℃)
Tj

Light Emitting Diode

Mounting board:

NCSW170C (Forward current IF=1(A), LED mounting pitch 1.75(mm))
Mounted to center when 1 piece.
TJ measured center LED when mounted 5 pieces.
Al-based PCB (Size 40×40×1.5t(mm), Thickness of Cu layer 35(μm),
Thickness of insulating layer 120(μm))
A6063 (Size 80×80×25t(mm))
Flotherm

Measurement:LED
LED 11 piece
Measurement:
piece

90

Measurement:LED
LED 55 pieces
Measurement:
pieces80

Simulation:
1 piece
Simulation: LED
LED 1piece

70

Simulation:
LED 55pieces
Simulation: LED
pieces

60

50
0

2

4

6

8

Thermal conductivity
conductivity ofof insulating
Thermalinsulating layer
layer [W/mK](W/mK)

Figure 4. TJ vs. Thermal conductivity of insulating layerThis document contains tentative information, Nichia may change the contents without notice.
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Application Note
3.3 Comparison base material of PCB
LED Part No.:
Mounting board:

NCSW170C (Forward current IF=1(A), LED mounting pitch 1.75(mm))
Al-based PCB, Cu-based PCB (Size 40×40×1.5t(mm),Thickness of Cu layer 35(μm), Thickness of insulating layer 120(μm))
A6063 (Size 80×80×25t(mm))
Flotherm

Heatsink:
Simulation soft:40

Insulating layer
Al baseLED package(Ceramic)
SolderCu layerAl-based PCB

Insulating layer
Cu baseCu-based PCB

Figure 5. PCB and Cross section images

TA=25(℃)

120Al-based PCB,
Al-based
PCB, LED
LED1 1piece
piece

110

TTjJ (℃)[℃]

Light Emitting Diode40

LED package(Ceramic)
SolderCu layerCu-based PCB,
PCB, LED
Cu-based
LED1 1piece
piece

100

Al-based PCB,
PCB,LED
LED5 pieces
5 pieces
Al-based90

Cu-based
LED5 5pieces
piecesCu-based PCB, LED

Measurement

Al-based PCB,
Al-based
PCB, LED
LED1 1piece
piece

80

Cu-based PCB,
PCB, LED
Cu-based
LED1 1piece
piece
70

Al-based PCB,
PCB,LED
LED5 pieces
5 pieces
Al-based60

Simulation

Cu-based
LED5 5pieces
piecesCu-based PCB, LED

50
0

2

4

6

8

Thermalconductivityof insulating
layer(W/mK)
Thermalconductivityof insulating
layer[W/mK]

Figure 6. Result of comparison base material of PCB

There is no difference on TJ values between Al-based and Cu-based PCB at the above condition(PCB and heatsink), and the thermal conductivity of insulating layer is the dominated parameter to
TJ value. There is other design approach that a higher thermal conductivity of base material iseffectively to lower TJ value as mentioned in the section “3.5 Thermal bypass PCB”. Please refer it
as well.

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Application Note
3.4 TJ comparison of the number of LED terminals
LED Part No.:NCSW170C, NCSW131C(Forward current IF=1(A), LED mounting pitch 1.75(mm))
Al-based PCB (Size 40×40×1.5t(mm), Thickness of Cu layer 35(μm),
Thickness of insulating layer 120(μm))
A6063 (Size 80×80×25t(mm))
Flotherm

Mounting board:
Heatsink:
Simulation soft:

40

40

40

for 2 terminal LED

for 3 terminal LED

Figure 7. Evaluation PCB

TA=25(℃)

120

NCSW170C
piece
NCSW170C 11piece

110

NCSW131C 11piece
NCSW131C
piece

100

T
[℃]
TjJ (℃)

Light Emitting Diode40

NCSW170C
piecesNCSW170C 55pieces

Measurement

NCSW131C
piecesNCSW131C 55pieces

90

NCSW170C
piece
NCSW170C 11piece

80

NCSW131C
piece
NCSW131C 11piece
70

NCSW170C 55pieces
NCSW170C
pieces60

Simulation

NCSW131C 55pieces
NCSW131C
pieces

50
0

2

4

6

8

Thermal conductivity
conductivity ofof insulating
Thermalinsulating layer
layer [W/mK](W/mK)

Figure 8. TJ vs. the number of LED terminals(NCSW170C: 2 terminals, NCSW131C: 3 terminals)

As the above evaluation results show, there are no significant differences on TJ values between 2
terminal LED and 3 terminal LED in both results of measurement and simulation.

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Application Note
3.5 Thermal bypass PCB
As shown in section 3.4, TJ value might exceed 90℃ at the condition of TA=25℃ when mounting
multiple LEDs on PCB. This means that TJ value is possibly to exceed 150℃ as the absolute
maximum rating at hot ambient such as TA=85℃. In such case, it is necessary to review the thermal
design. This section introduces the following PCB as a method for more improving thermal
management.
LED Part No.:
Mounting board:

NCSW131C (Forward current IF=1(A), LED mounting pitch 1.75(mm))
Cu-based thermal bypass PCB (Size 40×40×1.5t(mm),Thickness of Cu layer 35(μm), Thickness of insulating layer 120(μm))
A6063 (Size 80×80×25t(mm))
Flotherm

40

40

Thermal bypass AreaA

LED package(Ceramic)
SolderCu layerA'

Thermal bypass
Insulating layer
Cu baseA

A'

Figure 9. Thermal bypass PCB images
TA=25(℃)

120110TTjJ (℃)[℃]

Light Emitting Diode

Heatsink:
Simulation soft:

Al-basedAl-based PCB
PCB
Cu-basedCu-based PCB
PCB

100

Measurement

Al-basedAl-based PCB
PCB
Cu-basedCu-based PCB
PCB

90

Simulation

Cu-basedthermal
thermalbypass
bypassPCB
PCB
Cu-based
80

70
0

2

4

6

8

Thermalconductivity
conductivityofofinsulating
insulatinglayer
layer (W/mK)[W/mK]
ThermalFigure 10. Evaluation result of Thermal bypass PCB
Thermal bypass PCB is expensive design due to complex structure, however it is effective to control
for lower TJ. If there is not enough margin on TJ value, for example, much heat generating situations
as mounting multiple LEDs, this design becomes the effective method for enhancing heat radiation.
Thermal bypass structure is recommended for the 3 terminals LED type that includes non-electrical
pad such as Chip heatsink and electrical conductive 2 terminals, avoiding the failure of electricalcircuit.
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Application Note
3.6 Clearance of mounting LEDs
The clearance of mounting LED is effect to TJ value when mounting multiple LEDs. The narrow
clearance is advantageous on considering of optical design, but it needs notice that TJ value become
higher as the possible followed phenomenon.
LED model No.:
Mounting board:

TA=25(℃)

110100Al-based PCB
Al-based
PCB

Tj
TJ [℃](℃)

Light Emitting Diode

Heatsink:
Simulation soft:

NCSW131C (Forward current IF=1(A), Mounting LED 5 pieces)Al-based PCB, Cu-based PCB, Cu-based thermal bypass PCB(Size 40×40×1.5t(mm), Thickness of Cu layer 35(μm),
Thickness of insulting layer 120(μm))
A6063 (Size 80×80×25t(mm))
Flotherm

Cu-basedCu-based PCB
PCB

90

Cu-basedCu-based thermal
thermal bypass
bypass PCB

80

70
0.0

0.2

0.4

0.6

0.8

Clearance of mounting [mm]Clearance of mounting (mm)Figure 11. TJ vs. Clearance of mounting LED (Simulation)

Clearance
0.3

Pitch
1.75

0.3

a) Clearance 0.3(mm)

0.5

1.95

0.3

b) Clearance 0.5(mm)

0.7

2.15

0.3

c) Clearance 0.7(mm)Figure 12. Clearance of mounting LED images (Ex.: Cu-based thermal bypass PCB)This document contains tentative information, Nichia may change the contents without notice.
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Application Note
4. Thermal design for FR-4
A The thermal design for FR-4 is explained in following sections. These items are introduced as thepoints for thermal design.
A) Pattern (area size) and thickness of Cu layerB) Through-HoleC) Combination with heatsink

si
ze

Di

Hole size

an

Ho
le

st
ce

Cu layer
FR-4

Distance
Thickness of side Cu layer

Figure 13. Through-hole of FR-4 image

4.1 Effects of Through-hole
LED Part No.:
Mounting board:
Heatsink:
Simulation soft:

NCSW170C (Forward current IF=1(A), Mounting LED 1 piece)
FR-4 (Size 30×70×1.6t(mm), Thickness of Cu layer 70(μm))
Through-hole (Thickness of side Cu layer 35(μm))―
Flotherm

70

30Light Emitting DiodeThe effect of area size and thickness of Cu layer is the same as metal-based PCB, bigger area andthickness size are effective to heat radiation as for (A). In (B) section: the hole size, position(distance from LED), number of holes, and thickness of side Cu layer of Through-hole are the related
factors for heat radiation.

LED mounting side (Front side)

Back side

Figure 14. FR-4 image of Through-hole evaluation
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Application Note
TA=25(℃)

135

130

Tj
TJ [℃](℃)

125

Distance 1.0[mm]1.0(mm)Distance
Distance
Distance 1.5[mm]1.5(mm)120

Distance
Distance 2.0[mm]2.0(mm)

115

110
0

5

10

15

20

Figure 15. TJ vs. Through-hole 1 (Number of holes and distance)

TA=25(℃)

135130Hole size
size 0.3[mm]0.3(mm)

TJ [℃](℃)
Tj

Light Emitting Diode

Number of
Numberof holesholes

Hole size
Hole
size 0.4[mm]0.4(mm)125

Hole size
size 0.6[mm]0.6(mm)Hole size
size 0.8[mm]0.8(mm)
120

115
0

5

10

15

Number ofof holesNumberholes

Figure 16. TJ vs. Through-hole 2 (Number of holes and hole size)

Increasing the number of holes and the bigger hole size make effective to heat radiation, but toolarge number of holes or too big hole size do not have effect. And the cost of hole processing isgetting expensive when increasing the number of holes. It is important to find the balance between
heat radiation effect and cost.

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Application Note
4.2 Pattern of Cu layer
The pattern of Cu layer with using lead-frame package LED is often designed an asymmetry pattern,
as shown the right image in Table 3. But the Nichia 170 and 131 Series LEDs are ceramic packages,
and that radiate heat uniformly from both electrode (anode and cathode), therefore the symmetry
pattern is effective for heat radiation of the Nichia 170 and 131 Series LEDs, as shown the left in
Table 3.
Also, when designing Through-hole both anode and cathode, it is necessary to countermeasure to
avoid short-circuit such as setting space on back side of PCB because the structure related to theelectrical potentials of anode and cathode.

Heatsink:
Simulation soft:

NCSW170C (Forward current IF=1(A), Mounting LED 1 piece)
FR-4 (Size 30×70×1.6t(mm), Thickness of Cu layer 70(μm))
Through-hole (Hole size 0.4(mm), Thickness of side Cu layer 35(μm))―
Flotherm

Table 3. Comparing the effect of Cu layer pattern on FR-4 (Simulation)
Symmetry pattern

Asymmetry pattern
70

30

70

30

Light Emitting DiodeLED Part No.:
Mounting board:

Cu layer pattern

LED mounting side (Front side)

LED mounting side (Front side)

Back side

Back side

121 (℃)

136 (℃)

Through-hole
pattern

LED TJ

TJ value is 120℃ or more at the condition of TA=25℃ in the above result, it is not enough margin
to the higher TJ, estimated high temperature ambient condition such as TA=85℃. TJ can be lower
by increasing the board size of FR-4 or by using a heatsink. But if it is not possible to control TJ
lower sufficiently with the thermal designed PCB and heatsink, it needs to reduce the driving currentof LED. The luminous flux become lower by reducing the driving current of LED, but it is important
to design not to exceed the absolute maximum rating of TJ value.
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Application Note
4.3 Size of FR-4
TJ can be lower by the thermal design as increasing board size and area size of Cu layer of FR-4.
The result of thermal simulation with larger board size is shown below.
LED Part No.:
Mounting board:

NCSW170C (Forward current IF=1(A), Mounting LED 1 piece)
FR-4 (Thickness of board 1.6(mm), Thickness of Cu layer 70(μm))
Through-hole (Hole size 0.4(mm), Thickness of side Cu layer 35(μm))―
Flotherm

70
66

70

35

50

70

15

25

30

66
70

46
50

26
30

Figure 17. FR-4 images of comparison board size

TA=25(℃)

130

120

110

Tj
TJ [℃](℃)

Light Emitting Diode

Heatsink:
Simulation soft:

numberNumber ofof holes:holes: 66

Number ofof holes:holes: 10
10number

100

90

80

0

20

40

60

80

Board widths
widths ofBoardof FR-4
FR-4 [mm](mm)Figure 18. TJ vs. Board size of FR-4 (Simulation)
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Application Note
5. Summary
This document explained about the basic thermal design for LED mounting board in order to manage
TJ of LED under appropriate zone. Please make sure that TJ does not exceed the absolute maximum
rating.

Light Emitting DiodeIn addition, the measurement and simulation results of the thermal design, described as examples inthis document, it is not reproductions of the user’s usage environment such as individual heatsink
and housing structure. Please make sure TJ behaviors at user’s actual thermal design.

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Application Note
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.

Light Emitting Diode・ 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
Nichia, republication, reproduction, and/or redistribution of the content of this document in any
form or by any means, whether in whole or in part, including modifications or derivative works
hereof, is strictly prohibited.

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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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