Application Note

Light Emitting Diode

Solder Crack Considerations forLEDs for General Lighting

Table of Contents
1. Overview ........................................................... 2
2. Applicable Part Numbers .................................. 2
3. Main Cause of Solder Cracks............................ 3
4. Reducing the Occurrence of Solder Cracks ...... 4
5. Solder Crack Evaluation ................................... 8
6. Summary ......................................................... 13

NVSL119B-V1, NVSL219B-V1, NVSL119C, NVSL219C, and NVSW219F-V1 refer toNichia part numbers. These Nichia part numbers 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.
SP-QR-C2-210926-3
1/14
Feb. 5, 2024

Application Note
1. Overview

Light Emitting DiodeIn products using LEDs, the LEDs are usually soldered on PCBs, and the applications andenvironments in which the LED-mounted PCBs are actually used are becoming more diverse. Whenan LED-mounted PCB is repeatedly turned on and off under operating conditions that lead to a large
temperature difference and/or in an environment where the temperature fluctuates significantly,
solder cracks may occur depending on the combination of the package of the LED and the PCB
used (See Figure 1).
When the difference in the coefficient of thermal expansion (CTE) between the package of the LED
and the PCB used is large, solder cracks are more likely to occur and this may cause the LED not toemit light. Therefore, sufficient verifications must be done prior to use to ensure there are no issues
for the chosen application.

Solder Crack

Solder Crack

Electrode: Cathode

Electrode: Anode

Figure 1. Cross-sectional Observation of an LED Solder Joint Area (After a Temperature Cycle Test)

This application note explains how solder cracks occur and provides examples of reducing theoccurrence of solder cracks. Solder crack evaluations were conducted through temperature cycle
tests using combinations of typical packages of LEDs and PCBs. The evaluation results are also
included in this application note.

2. Applicable Part Numbers
This application note applies to the LEDs shown in Table 1.
Table 1. Applicable LED Part/Series Numbers
Middle Power
Category

Nichia 757 Series

Nichia 385 Series

Nichia 585 Series

Nichia T02 SeriesPart Number

NFxx757x

NF2W385x

NFxW585x

NSSxT02x

3.0mm×3.0mm

4.0mm×3.6mm

4.0mm×3.6mm

1.2mm×0.7mm

Examples of
Package Appearance
Package SizeHigh Power
Category

Nichia x19 Series

Nichia 519 Series

Nichia 719 Series

Nichia 48x SeriesPart Number

NxSx119/NxSx219

NVSW519x

NVSW719x

NFMW48xx

3.5mm×3.5mm

3.5mm×3.5mm

3.5mm×3.5mm

6.5mm×5.8mm

Examples of
Package Appearance
Package Size

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
2/14
Feb. 5, 2024

Application Note
Super High Power
Category

Nichia B35 Series

Nichia 144 Series

Nichia 149 SeriesPart Number

NV4WB35xNV4x144x

NV9W149x

3.5mm×3.5mm

5.0mm×5.0mm

7.0mm×7.0mm

Examples of Package
Appearance
Package Size

Light Emitting Diode

Direct Mountable Chip
Category

Nichia E11 Series

Nichia E13 Series

Nichia E17 Series

Nichia E21 SeriesPart Number

NFSWE11xNCSWE13xNCSxE17x

NVSxE21x

1.1mm×1.1mm

1.25mm×1.25mm

1.7mm×1.7mm

2.1mm×2.1mm

Examples of Package
Appearance
Package Size

3. Main Cause of Solder Cracks
3.1 Coefficient of Thermal Expansion (CTE)
Solder cracks are more likely to occur when the difference in CTE between the package of the LED
and the PCB is large.
The CTE describes how the length of an object changes with an increase in temperature.
Table 2 below shows the CTEs of typical package materials of LEDs and the CTEs of typical PCB
materials.
Note that the CTEs listed in Table 2 are only the typical values of the materials.
Table 2. CTEs of Typical Package Materials of LEDs and PCB Materials
Package materials of LEDs
Material

Category

CTE (1/°C)

Ceramic

5〜7×10-6

Nichia x19、519、719、B35、144、149 SeriesResin

14～20×10-6

Nichia 757、385、585、T02、48ｘ Series

PCB material

CTE (1/°C)

Ceramic

8×10-6Iron (Fe)

12×10-6

Glass-reinforced epoxy laminate material (FR-4)

14×10-6

Copper (Cu)

17×10-6

Aluminum (Al)

21×10-6Composite epoxy material (CEM-3)

25×10-6This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
3/14
Feb. 5, 2024

Application Note
3.2 How Solder Cracks Occur
Figure 2 below shows an LED soldered to a PCB. When the LED-mounted PCB is repeatedly turnedon and off under operating conditions that lead to a large temperature difference and/or in anenvironment where the temperature fluctuates significantly, the difference in the CTE between the
package of the LED and the PCB causes them to expand/contract at different rates and the resulting
stress will be applied to the solder joints (see Figure 3).
ExpandContract

LED
Stress is applied to thesolder joint.

SolderLight Emitting Diode

PCB

Figure 2. LED Soldered to a PCB

Figure 3. How Stress is Applied to the Solder Joints

If these solder joints are exposed to repeated stress, it will cause a minor crack to occur in the solder
joint. Then when it is exposed to additional stress, if the crack turns into a complete fracture, it stops
the flow of electrical current supplied to the LED, the LED will fail to illuminate (see Figure 4).
A solder crack
occurs in the solder
joint.

A solder crack grows and thesolder joint strength decreases,
causing the LED not to illuminate.

Figure 4. How Solder Cracks Occur

4. Reducing the Occurrence of Solder Cracks
Examples of measures to reduce solder cracks are as follows.
4.1 Using LEDs with a High Solder Crack Resistance- LEDs with Compact Package Sizes
By using an LED with a compact package size, effects due to the difference in the CTE between the
package of the LED and the PCB used under the temperature rise can be minimized, enabling theoccurrence of solder cracks to be reduced.
- LEDs with Short Distances between their Electrodes
By using an LED with a short distance between its electrodes, effects due to the difference in the CTE
between the package of the LED and the PCB used under the temperature rise can be minimized,
enabling the occurrence of solder cracks to be reduced.
- LEDs with Large Areas for their Electrodes
By using an LED with a large area for the electrodes, the strength of the solder joint increases,
enabling the occurrence of solder cracks to be reduced.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
4/14
Feb. 5, 2024

Application Note
4.2 Selecting a Combination where the CTE Difference between the Package of the LED and
the PCB is Small
As shown in Section 3.2 “How Solder Cracks Occur”, solder cracks can be reduced by selecting a
combination where there is a small difference in CTE between the package material of the LED and
the PCB material.
For example, when combining a resin package LED and a glass epoxy PCB, the CTE difference is
2x10-6, whereas when combining a ceramic package LED and an aluminum-core PCB, the CTE
difference is 16x10-6. It is considered that the combination of a resin package LED and a glass epoxy
PCB is effective for reducing solder cracks (See Figure 5).
25

Coefficient of Thermal
Expansion (CTE)(×10-6/℃)
線膨張係数(1×10-6/℃)

Light Emitting Diode

20

LED

PCB

15
10

Small
Difference

50Coefficient of Thermal
Expansion (CTE)-6/℃)(×10-6/℃)
線膨張係数(1×1025Less Solder Cracks

More Solder Cracks

PCB

20

15

Large
Difference

10
5

LED

0

樹脂パッケージ
Resin
Package

ガラスエポキシ基板
Glass
Epoxy PCB

セラミックパッケージ

アルミ基板

Ceramic Package Aluminum-core PCB

Figure 5. Differences in CTE between the Packages of the LEDs and PCBs

4.3 Using an Aluminum-core PCB Containing a Low Elastic Modulus Insulating Layer
In general, solder cracks can be reduced by using an aluminum-core PCB containing an insulating
layer with a low elastic modulus. An insulating layer with a low elastic modulus can deform to follow
the stress generated by the difference in CTE between the package material of the LED and the PCB
material, and thereby reducing stress on the solder joints (see Figure 6).

An insulating layer with a low
elastic modulus can reduce stressapplied to the solder joints.

Expansion
Contraction
Copper Layer
An Insulating Layer with a
Low Elastic Modulus
Aluminum-core PCB

Figure 6. Example of Aluminum-core PCB Containing an Insulating Layer with a Low Elastic Modulus

For reference, Figure 7 shows the deformation rates of the aluminum-core PCB insulating layers
against stress.
Under the same stress, the deformation rates of the aluminum-core PCB insulating layers with low
elastic moduli are larger than that of a standard aluminum-core PCB.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
5/14
Feb. 5, 2024

Application Note

(MPa)
Stress応力（MPa)Standard Aluminum-core PCB

Aluminum-core PCBs Containing Insulating Layers with
Low Elastic Moduli(The insulating layers can deform easily, enabling thestress onto the solder joints to be minimized)
0

0.02

0.04

0.06

0.08

変形量（％）
Deformation
Rate (%)

Figure 7. Deformation Rates of the Insulating Layers
Contained in Aluminum-core PCBs against Stress

Light Emitting Diode

When selecting an aluminum-core PCB, the storage modulus of the insulating layer of the PCB must
be checked (see Table 3). The storage moduli of aluminum-core PCBs are temperature-dependent andthe values also vary depending on the thicknesses of the insulation layers. Note that lowering thestorage modulus may decrease the thermal conductivity that is important for heat dissipation.
Even if an aluminum-core PCB containing an insulating layer with a low elastic modulus is selected,
it may not be effective for reducing solder cracks in some LEDs (e.g. LEDs with large package sizes).
Therefore, sufficient verifications must be performed by using the selected PCB to evaluate the solder
crack resistance.
Table 3. Insulating Layers of the Aluminum-core PCBs

Aluminum-core PCB1
Standard Insulating Layer
Low Elastic Modulus Insulating
Layer - A
Low Elastic Modulus Insulating
Layer - B

1

ThermalConductivity(W/m・K)
2.1

Storage Modulus (GPa)
Low
Room
High
Temperature
Temperature
Temperature(-40°C)(25°C)(125°C)
17
12
2.8

3.0

12

1.2

0.7

2.5

4.6

0.51

0.04

These PCBs were used for the solder crack evaluation in Section 5.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
6/14
Feb. 5, 2024

Application Note
4.4 Using a High Reliability Lead-free Solder Paste
Generally, the use of high reliability lead-free solder pastes, which can reduce the risks of occurrence
and progression of solder cracks, allows for a delay in the decrease in the solder joint strength. Thiscan delay the onset of solder cracks accordingly when compared with a standard lead-free solder paste(Sn-3.0Ag-0.5Cu).
It is generally known that when a standard lead-free solder paste is used under high temperatures
and/or when it undergoes repeated thermal shock, the crystal grains in the solder structure becomecoarse and the alloy layer grows, resulting in the decrease in the solder joint strength (see Figure 8).

Light Emitting Diode

Growth of
the Alloy Layer
Cu

Figure 8. Cross-sectional Views of the Solder Joint Area (Before and After the Temperature Cycle Test)

In recent years, there has been research and development done on solder pastes to maintain thereliability of solder joints even when an LED-mounted PCB is used under high temperatures and/or
when an LED-mounted PCB is repeatedly turned on and off under operating conditions that lead to alarge temperature difference and/or in an environment where the temperature fluctuates significantly.
However, when a high reliability lead-free solder paste is used as a measure to reduce solder cracks,
stress may become concentrated onto the LED due to a large difference in CTE between the packageof the LED and the PCB, leading to cracks and/or breakage of the LED chip. Take this into
consideration when selecting a solder paste. Table 4 shows the types of solder pastes and theprecautions.
Table 4. Types of Solder Pastes and the Precautions
Solder Paste2
Standard Lead-free Solder

Composition

Precaution

Sn-3.0Ag-0.5Cu－
Avoid using this solder paste

High Reliability Lead-free Solder

Sn-3.4Ag-0.7Cu-3.2Bi-3.0Sb-Ni-X

for Nichia’s E11, E13, E17,
E21 Series.

When a high reliability lead-free solder paste is used for the PCB assembled in the chosen application,
ensure that there are no issues with the solderability, solder voids, and reliability etc. prior to use.

2

These solder pastes were used for the solder crack evaluation in Section 5.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
7/14
Feb. 5, 2024

Application Note
5. Solder Crack Evaluation
5.1 Temperature Cycle Test 1
Nichia conducted temperature cycle tests on LED-mounted PCBs in different combinations of the
packages of LEDs and PCBs that were explained in Section 4. The test conditions and types of theLEDs and PCBs used, and the test results are as follows.
5.1.1 Test Conditions and Evaluation Materials
Conditions of the Temperature Cycle:-40℃ (15 min) ⇔ 100℃ (15 min), 2,000 cycles, not in operation

LEDs and PCBs Used:

See Tables 5 and 6, and Figure 9

Solder Paste Used:

Sn-3.0Ag-0.5Cu

Thickness of the Metal Solder Stencil: 100µm

Light Emitting Diode

Verification Method:

Lighting inspection, check for ΔVF 3, cross-sectional observation
Table 5. Evaluated LEDs

(7×10-6)

Qty. ofElectrodes2

Area of the Electrodes
(mm2)
8.3

Ceramic (AlN)(5×10-6)2

8.3

Ceramic (Al2O3)(7×10-6)3

6.2

Ceramic (AlN)(5×10-6)3

6.2

LED Part No.

Package Material

CTE (1/°C)

NVSL119B-V1

Ceramic (Al2O3)

NVSL119C
NVSL219C

NVSL119B-V1 and NVSL219B-V1
Size: 3.5mm × 3.5mm

NVSL119C and NVSL219C
Size: 3.5mm × 3.5mm

NVSL119B-V1 and
NVSL119C
Bottom Surface(Two Electrodes)
4.1
3.3
2.3
1.3

4.1

3.5

3.3

0.6

CathodeNVSL219B-V1 and
NVSL219C
Bottom Surface(Three Electrodes)

Anode

NVSL119B-V1 and NVSL119C
Soldering Pad Pattern (Two Electrodes)

CathodeDie Heat Sink

1.2

NVSL219B-V1

Anode

NVSL219B-V1 and NVSL219C
Soldering Pad Pattern (Three Electrodes)

Figure 9. Evaluated LEDs and the Soldering Pad Patterns
When solder cracks occur in an LED, the electrical resistance at the solder joints becomes large and the forward voltage (VF) tends toincrease; the VF is used as a reference value for occurrence of solder cracks. The increase rate of the forward voltage (ΔVF) represents inpercentage how much of VF increases from the initial VF.
ΔVF ≥10% , which has been used for Nichia’s reliability tests as the judgement criterion, is also used in the solder crack evaluations.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
8/14
Feb. 5, 20243

Application Note
Table 6. PCBs Used

Iron (Fe)

12×10-6

PCB Thickness
(mm)
0.5

Glass Epoxy (FR-4)

14×10-6

1.0

35

-

Aluminum (Al)

21×10-6

1.0

35

120

PCB

CTE (1/°C)

Copper Layer
Thickness (μm)
35

Insulating Layer
Thickness (μm)
1205.1.2 Test Results
The temperature cycle tests were conducted up to 2000 cycles. As a result, no lighting failure 4
occurred in any of the combinations of the packages of LEDs and PCBs; however, the forward voltage
did increase at 1000 cycles onward for the combination of the aluminum-core PCB and the LEDs
with small areas for their electrodes, where the CTE difference is large (see Tables 7 and 8).

Light Emitting Diode

Table 7. Temperature Cycle Test Results (Number of the LEDs that Failed to Emit Light)
PCB Material
Number of
CyclesNVSL119B-V1

Iron (Fe)Glass Epoxy (FR-4)

Aluminum (Al)

500

1000

1500

2000

500

1000

1500

2000

500

1000

1500

2000

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

NVSL119C

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

NVSL219B-V1

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

NVSL219C

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

Table 8. Temperature Cycle Test Results (Number of the LEDs with ΔVF ≥10%)
PCB Material
Number of
CyclesNVSL119B-V1

Iron (Fe)Glass Epoxy (FR-4)

Aluminum (Al)

500

1000

1500

2000

500

1000

1500

2000

500

1000

1500

2000

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

NVSL119C

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

NVSL219B-V1

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

1/10

7/10

7/10

NVSL219C

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

5/10

7/10

8/10

The combinations of the LED and the iron PCB and of the LED and the glass epoxy PCB, where theCTE difference is small, no ΔVF ≥10% occurred. When comparing the LEDs based on the different
electrode areas, the LEDs with large areas for their electrodes are more effective in reducing solder
cracks than those with small areas for their electrodes (see Table 9).
Table 9. Combination of the LEDs and PCBs
(CTE differences in red indicate that the combinations led toΔVF ≥10%)

4

Iron (Fe)Glass Epoxy (FR-4)

Aluminum (Al)2

Area of theElectrodes
(mm2)
8.3

5×10-6

7×10-614×10-6

NVSL119C

2

8.3

8×10-6

10×10-6

17×10-6

NVSL219B-V1

3

6.2

5×10-6

7×10-614×10-6

NVSL219C

3

6.2

8×10-6

10×10-6

17×10-6

LED Part No.

Qty. ofElectrodes

NVSL119B-V1

CTE Difference between the LED and the PCB (1/°C)

The lighting failure stated in this application note means that an LED does not illuminate due to an open circuit.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
9/14
Feb. 5, 2024

Application Note
5.2 Temperature Cycle Test 2
In Section 4, Nichia explained examples of measures to reduce solder cracks: selecting a PCB
containing an insulating layer with a low elastic modulus and using a high reliability lead-free solder
paste. For these measures, Nichia performed temperature cycle tests and the test results are shown
below.
5.2.1 Test Conditions and Evaluation Materials
Conditions of the Temperature Cycle:-40℃ (15 min) ⇔ 100℃ (15 min), 2,000 cycles, not in operation

LEDs and PCBs Used:

See Tables 10 and 11, and Figure 10

Solder Paste Used:

See Table 12

Verification Method:

Lighting inspection, check for ΔVF 3, cross-sectional observation

LED Part No.

Package Material

CTE (1/°C)

Qty. of Electrodes

Area of the Electrodes (mm2)

NVSW219F-V1

Ceramic (AlN)

5×10-63

6.2

NVSW219F-V1
Bottom Surface(Three Electrodes)

NVSW219F-V1
Size: 3.5mm × 3.5mm

1.2

4.1
3.3
2.3
1.3

3.3

Light Emitting Diode

Table 10. Evaluated LED

CathodeDie Heat Sink

Anode

NVSW219F-V1
Soldering Pad Pattern(Three Electrodes)

Figure 10. Evaluated LED and the Soldering Pad Patterns
Table 11. PCBs Used
Type of Aluminumcore PCB

Storage Modulus at
25℃ (GPa)

Thickness of theAluminum (mm)Thickness of
the Copper
Layer (μm)

Thickness of theInsulating Layer
(μm)

12

1.0

35

120

1.2

1.0

35

120

0.51

1.0

35

100

Standard Insulating
Layer
Low Elastic Modulus
Insulating Layer - A
Low Elastic Modulus
Insulating Layer - B

Table 12. Types of Solder Pastes and Thickness of the Metal Solder Stencil
Solder Paste
Standard Lead-free Solder
High Reliability Lead-free Solder

Sn-3.0Ag-0.5Cu

Thickness of Metal Solder Stencil
(μm)
100

Sn-3.4Ag-0.7Cu-3.2Bi-3.0Sb-Ni-x

100

Composition

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
10/14
Feb. 5, 2024

Application Note
5.2.2 Test Results
Using an Aluminum-core PCB Containing a Low Elastic Modulus Insulating Layer
When the standard aluminum-core PCB was used, the forward voltage increased at 1000 cycles
onward, whereas when the aluminum-core PCB containing an insulating layer with a low elastic
modulus (A) was used, the increase in the forward voltage was delayed to 2000 cycles. When anotheraluminum-core PCB containing an insulating layer with a low elastic modulus (B) was used, noincrease in the forward voltage occurred within 2000 cycles (see Figure 11 and Table 13).
順電圧(%)
Relative Forward
Voltage (%)

Standard Aluminum-core PCB

115
110

PCB A (Low Elastic Modulus Insulating Layer)

105
100

PCB B (Low Elastic Modulus Insulating Layer)

95
90
0

500
1000
1500
温度サイクル（-40℃～100℃）

2000

Temperature Cycle (-40℃ to 100℃)

Figure 11. Temperature Cycle Test Results (Average Forward Voltage)
Table 13. Temperature Cycle Test Results (Number of the LEDs with ΔVF ≥10%)
Aluminum-core PCB
Standard Insulating Layer
Low Elastic Modulus
Insulating Layer - A
Low Elastic Modulus
Insulating Layer - B

Solder Paste
Standard Lead-free
Solder Paste
Standard Lead-free
Solder Paste
Standard Lead-free
Solder Paste

500 Cycles

1000 Cycles

1500 Cycles

2000 Cycles

0/20

18/20

20/20

20/20

0/20

0/20

0/20

2/20

0/20

0/20

0/20

0/20

Using a High Reliability Lead-free Solder Paste
When the standard lead-free solder paste was used, the forward voltage increased at 1000 cycles
onward, whereas when a high reliability solder paste was used, the increase in the forward voltage
was delayed to 1500 cycles (see Figure 12 and Table 14).
120

Voltage (%)
Relative Forward
順電圧(%)

Light Emitting Diode

120

115

Standard Lead-free Solder Paste

110

High Reliability Lead-free Solder Paste

105
100
95
90
0

500
1000
1500
温度サイクル（-40℃～100℃）

2000

Temperature Cycle (-40℃ to 100℃)

Figure 12. Temperature Cycle Test Results (Average Forward Voltage)
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
11/14
Feb. 5, 2024

Application Note
Table 14. Temperature Cycle Test Results (Number of the LEDs with ΔVF ≥10%)
Aluminum-core PCB
Standard Insulating
LayerStandard Insulating
Layer

Solder Paste
Standard Lead-free
Solder Paste
High Reliability Leadfree Solder Paste

500 Cycles

1000 Cycles

1500 Cycles

2000 Cycles

0/20

18/20

20/20

20/20

0/20

0/20

2/20

14/20

Using an Aluminum-core PCB Containing a Low Elastic Modulus Insulating Layer and a High
Reliability Lead-free Solder Paste
When aluminum-core PCBs containing a low elastic modulus insulating layers and a high reliability
lead-free solder paste were used, no increase in the forward voltage occurred within 2000 cycles (seeFigure 13 and Table 15).
順電圧(%)
Voltage (%)
Relative Forward

Light Emitting Diode

120

Standard Aluminum-core PCB,
Standard Lead-free Solder Paste

115
110

See Table 16 for the Cross-Sectional Analysis

105
100

PCB A and B (Low Elastic Modulus),
High Reliability Lead-free Solder Paste

95
90
0

500
1000
1500
温度サイクル（-40℃～100℃）

2000

Temperature Cycle (-40℃ to 100℃)

Figure 13. Temperature Cycle Test Results (Average Forward Voltage)
Table 15. Temperature Cycle Test Results (Number of the LEDs with ΔVF ≥10%)
Aluminum-core PCB
Standard Insulating
Layer
Low Elastic Modulus
Insulating Layer - A
Low Elastic Modulus
Insulating Layer - B

Solder Paste
Standard Lead-free
Solder Paste
High Reliability Leadfree Solder Paste
High Reliability Leadfree Solder Paste

500 Cycles

1000 Cycles

1500 Cycles

2000 Cycles

0/20

18/20

20/20

20/20

0/20

0/20

0/20

0/20

0/20

0/20

0/20

0/20

The cross-sectional analysis results at 2000 cycles are shown in Table 16 for reference.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
12/14
Feb. 5, 2024

Application Note
Table 16. Cross-sectional Analysis Results
Materials Used

CathodeChip Heatsink

Anode

100%

100%

100%

0%

0%

0%

Standard Aluminum-core
PCB and Standard Leadfree Solder Paste

Light Emitting Diode

Ratio of Solder Cracks5
PCB B (Low Elastic
Modulus Insulating
Layer) and High
Reliability Lead-free
Solder Paste
Ratio of Solder Cracks56. Summary
When an LED-mounted PCB is repeatedly turned on and off under operating conditions that lead toa large temperature difference and/or in an environment where the temperature fluctuates significantly,
solder cracks can occur, and this may cause the LED not to emit light.
As examples of measures to reduce solder cracks, this application note explains suitable combinationsof the package materials of LEDs and PCBs, use of aluminum-core PCBs containing low modulus
elasticity insulating layers, and use of high reliability lead-free solder pastes for reference purposes.
When designing the chosen application, the solder joint temperature and the environment where thechosen application is actually used must be sufficiently verified. If the solder joint temperature tends
to be high, a suitable thermal design must be required to prevent excess stress on the solder joints. In
addition, the lifetime required for the chosen application must be considered when measures to reduce
solder cracks are taken.
In the final design stage, considering the PCB and the solder paste selected for the chosen applicationand the environment where the chosen application is actually used, ensure that there are no adverse
effects on the solder joints and that the lifetime required by the chosen application is maintained.
The cross-sectional images in Figures 1 and 8 and Table 16 were taken by Qualtec Co., Ltd.

5 Ratio of Solder Crack (%) = The length of a solder crack / The length of the electrode of the solder joint × 100

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
13/14
Feb. 5, 2024

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.

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

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210926-3
14/14
Feb. 5, 2024