Application Note

Light Emitting DiodeLED Pitch and Heat Dissipation
Performance (5-10mm Pitch)

Table of contents
1. Objective ...................................................................................... 2
2. Materials and Procedures ...................................................... 2
3. LED Models for Demonstration ........................................... 3
4. TJ Measurement Results According to each Pitch ......... 4
5. Conclusion ................................................................................... 7

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Application Note
1. Objective

Light Emitting Diode

When LEDs are used for a lighting fixture, in general, multiple LEDs, not a single one, areinstalled in the unit.
Operating a single LED generates high heat; all the more heat is generated when multiple
LEDs are mounted on a board due to the mutual effect. Then, the junction temperature(hereinafter referred to as TJ) of each LED gets higher, than in a single usage, leading tothe decrease in their lifetimes and their luminous flux.
Minimizing TJ equates to better thermal management, allowing for a longer lifetime.
Therefore, LEDs must be mounted with the optimal pitch among them.
This document shows the optimal pitch between LEDs by demonstrating someconfigurations.

2. Materials and ProceduresFirst, we prepared and used the aluminum board (hereinafter referred to as AL) and theglass epoxy board (hereinafter referred to as FR-4) as follows (cf. Table 1). Then, wemounted 9 LEDs on each board according to the simulation pitches (cf. Table 2). Please
note that the pitch is the distance between the centers of an LED and its neighboring one(cf. Figure 1).
Table1. Testing Board
Aluminum on

Glass Epoxy on

either surface

both surfaces

Pitch
ピッチ3mm3mm

Top Surface

Figure 1. Pitch
Reverse Surface

Thickness

1.0 mm
35μm

Copper Foil Thickness
Insulating Layer Thickness

1.6 mm120μm

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Application Note
Second, the LEDs were operated in a closed environment for 15 minutes. Then, when thetemperature was saturated, the soldering temperature (hereinafter referred to as Ts) of thecathode side of the LED located in the center was measured. Figure 2 shows the Ts
measurement point.
Table 2. Pitch PatternLight Emitting Diode

5mm Pitch

6mm Pitch

7mm Pitch

10mm Pitch

Figure 2. Ts Measuring Point

3. LED Models for Demonstration
We demonstrated the configurations by using the 2 models below:
Table 3. LEDs for Demonstration
LED Models

Part No. NS2W757A-V1

Part No. NF2W757AR-V1

Overview

Dimensions [mm]3.0×3.0×0.52

Forward Current [mA]

65

150

Maximum Forward Current [mA]

180200Forward Voltage [V]

2.85

6.3

Maximum Junction Temperature [°C]120This document contains tentative information, Nichia may change the contents without notice.
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Application Note
4. TJ Measurement Results According to each Pitch
4.1 Part No. NS2W757A-V1
Figure 3 shows the TJ measurement results at 4.1W (IF=150 mA) and 1.7W (IF=65 mA)
according to the specified pitches. On the FR-4, the LED pitches did not affect the TJ much,when the input powers were low; however, when the input powers were increased, the TJ
varied depending on the LED pitches: The smaller the LED pitch was, the higher the TJ
became. On the other hand, there was no difference in the TJ values on the AL, regardlessof the LED pitches.
Part No. NS2W757A-V1 Pitch of LED vs. TJ

TA=25°C
4.1W (IF=150mA)
FR-4 : 4.1W
FR-4:
(IF=150mA)

FR-4:(IF=65mA)
1.7W (IF=65mA)
FR-4 : 1.7W
TJ max 120°C

125

AL:
(IF=150mA)
4.1W (IAL : 4.1W
F=150mA)
AL:
F=65mA)(IF=65mA)
1.7W (IAL : 1.7W

100

TJ [°C]Light Emitting Diode150755025456789101112Pitch of LED [mm]Figure 3. Junction Temperature According to LED Pitch (Part No. NS2W757A-V1)

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Application Note
4.2 Part No. NF2W757AR-V1
Figure 4 shows the TJ measurement results at 8.5W (IF=150 mA) and 5.7W (IF=100 mA)
according to the specified pitches. The TJ values on FR-4 were affected by the LED pitches:
The smaller the LED pitches were, the higher the TJ became. On the other hand, there waslittle difference in the TJ values on the AL, regardless of the LED pitches.
Part No. NF2W757AR-V1 Pitch of LED vs. TJ

200

TA=25°C

FR-4:: 8.5W
(IF=150mA)
8.5W (IFR-4
F=150mA)
FR-4:: 5.7W
(IF=100mA)
5.7W (IFR-4
F=100mA)

175

AL:: 8.5W
F=150mA)(IF=150mA)
8.5W (IAL
AL:: 5.7W (IF=100mA)(IF=100mA)
AL

TJ [°C]Light Emitting Diode

150TJ max 120°C

125
1007550456789101112Pitch of LED [mm]Figure 4. Junction Temperature According to LED Pitch (Part No. NF2W757AR-V1)
As shown in Figure 4, the TJ slightly increased, as the LED pitch got smaller. The aluminumboard has a higher thermal conductivity than the FR-4, diffusing heat over the board moreeasily. Therefore, the heat can be dispersed even when the LED pitch is small.

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Application Note
On the AL, there was little difference in the TJ values depending on the LED pitches. Then,
we evaluated the TJ by increasing the amount of the LEDs mounted on the board and theinput power more.
Part No. NF2W757AR-V1 Pitch of LED vs. TJ

TA=25°C, IF =100mA

225

FR-4
FR-4:: 15.8W (25pcs)(25pcs)
FR-4
FR-4:: 5.7W (9pcs)(9pcs)

200

AL
AL:: 15.8W (25pcs)(25pcs)175

AL
AL:: 5.7W (9pcs.)(9pcs)

150

TJ [°C]

TJ max 120°C

Light Emitting Diode

125
100755025456789Pitch of LED [mm]101112Figure 5. Junction Temperature According to LED Pitch (Part No. NF2W757AR-V1)(Higher Input Power, 25 LEDs mounted)
On the FR-4, the TJ significantly increased, as the LED pitches became smaller. Therefore,
the LED pitches thermally impact on the LED-mounted board. On the other hand, the TJ
was not significantly affected by the LED pitches on the AL.
Please note that we performed the test above the TJ max. If LEDs are used above the TJ
max in practical use, they can burn out as seen in Figure 6. Customers should take care soas not to operate the LEDs above the TJ max with proper heat dissipation system such asheat sinks.

Figure 6. LED Burnout Damage
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Application Note

Light Emitting Diode5. Conclusion
Based on the evaluation results, it has been determined that the TJ is affected by the LED
pitch and the input power (W). The optimal pitch between LEDs needs to be designed
according to the input power (W). Customers should take care of the board’s thermal
conductivity in designing the LED pitch.
When the FR-4 is used, heat cannot be easily dispersed due to its low thermal conductivity.
Therefore, when the LED pitch is small on the FR-4, heat is excessively increased due to themutual interaction of the LEDs.
On the other hand, heat can be easily dispersed on the AL due to its high thermal
conductivity. Therefore, the AL can reduce the rise in temperature even with the narrow
pitch due to lower mutual interaction of the LEDs.
Please design the LED configuration to reduce the influence by heat, by referring to thesimulation data shown herein. Your product can thus sustain a long lifetime and maintainthe best optical characteristics.
Please use this document as reference, since the measurement data varies depending on
LED model and usage conditions/environment at customer sites.
We appreciate your understanding and cooperation.

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Application Note

Light Emitting DiodeDisclaimer
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