Application Note

Light Emitting Diode

Solder Crack Considerations for LEDs
for Automotive Applications

Table of Contents
1. Overview ........................................................... 2
2. Applicable Part Numbers .................................. 2
3. Main Cause of Solder Cracks............................ 4
4. Reducing the Occurrence of Solder Cracks ...... 5
5. Solder Crack Evaluation ................................. 10
6. Summary ......................................................... 18

NCxW121x, NCxx131x, Nxxx170x, NJxW270x, NxSx123x, NxSx172x, NCxW093x, NxSx146x,
NCxW193x, NxSx572x, NHSx046x, NSSx063x, NxSx064x, NSSx088x, NSSW129, NSSM313x,
and NSSM438x refer to Nichia part numbers. These Nichia part numbers within this document are
merely Nichia’s part numbers for those Nichia products and are not related nor bear resemblance toany other company’s product that might bear a trademark.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
1/19
Jul. 31, 2023

Application Note
1. Overview

Light Emitting Diode

LEDs are usually mounted on PCBs by using solder. When an LED-mounted PCB is repeatedly
turned on and off under operating conditions that lead to a large temperature difference and/or in anenvironment where the temperature fluctuates significantly, thermal stress may cause cracks in thesolder joint (see Figure 1). Solder cracks are more likely to occur when the difference in thecoefficient of thermal expansion (CTE) between the package of the LED and the PCB is large. Whenthe solder crack grows, it may cause a solder joint failure, causing the LED not to emit light.
Therefore, sufficient verifications must be done before soldering the LEDs.
This application note explains how solder cracks occur and provides examples of reducing theoccurrence of solder cracks together with the results of a thermal shock test (temperature cycle test).

Solder Crack

Figure 1. Example of a Solder Crack

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

Part
NumberNichia 131/170 Series1

Nichia 121 Series

Category

NC2W121x

NC3W121x

NC4W121x

NC5W121x

NCSx131x
NCSx170xNC2x131xNC2x170x

NJSx170x

3.1×2.6×0.75

3.1×3.75
×0.75

3.1×4.9×0.75

3.1×6.05
×0.75

1.8×1.45×0.75

3.0×1.6×0.75

1.6×1.2
×0.75

Example of
Package
Appearance
Package
Size(Unit: mm)

1

The electrode pattern on the back of the package for the Nichia 131 Series and Nichia 170 Series is different.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
2/19
Jul. 31, 2023

Application Note
CategoryPart
NumberNichia 270 Series
NJ2W270x

Nichia 123 Series

NJ3W270x

NFSx123x

Nichia 172 Series

NJSx123x

NFSx172x

NJSx172x

Example of
Package
Appearance
Package
Size(Unit: mm)

3.5×3.5×0.75
Nichia 093 Series

Category

Light Emitting Diode

Part
Number

2.0×3.0×0.7

NC2W093x

NC3W093x

3.0×3.0×0.8
Nichia 146 Series

NC4W093x

NC5W093x

NESx146x

NHSx146x

NSSx146x

Example of
Package
Appearance
Package
Size(Unit: mm)

8.5×8.0×1.5
Nichia 193 Series

CategoryPart
Number

1.4×2.2×0.7

NCSW193x

NC2W193x

NC3W193x

Nichia 572 Series
NC4W193x

NC5W193x

NJSx572x

NSSx572x

Example of
Package
Appearance
Package
Size(Unit: mm)

11.8×8.0×1.7

3.0×3.0×0.7

Category

Nichia 046 Series

Nichia 063 Series

Nichia 064 Series

Part
NumberNHSx046x

NSSx063x

Package
Size(Unit: mm)

1.4×2.2×1.3

2.8×3.5×2.0

Category

Nichia 088 Series

Nichia 129 Series

Nichia 313 Series

Nichia 438 Series

Part
NumberNSSx088x

NSSW129

NSSM313x

NSSM438x

1.4×3.5×1.2

3.6×4.0×4.0

3.3×3.3×1.8

1.6×4.7×1.8

NESx064x

NHSx064x

NSSx064x

Example of
Package
Appearance

2.8×3.5×2.0

Example of
Package
Appearance
Package
Size(Unit: mm)

The x represents a letter that follows the alphanumeric code of the same LED type. (e.g.: NCSx170x ・・・
NCSW170D, NCSW170F, NCSY170F, NCSA170G, NCSW170G, NCSW170G-SA etc.)
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
3/19
Jul. 31, 2023

Application Note
3. Main Cause of Solder Cracks
The following shows how solder cracks occur.
Figure 2 shows an LED soldered to an aluminum-core PCB.
LED
Insulating Layer

SolderCopper Layer
Aluminum-core PCB

Light Emitting Diode

Figure 2. LED Soldered to an Aluminum-core PCB
When the LED-mounted PCB is repeatedly turned on and off under operating conditions that leadto a large temperature difference and/or in an environment where the temperature fluctuatessignificantly, the difference in the coefficient of thermal expansion (CTE) between the package of
the LED and the aluminum-core PCB causes them to expand/contract at different rates and theresulting stress will be applied to the solder joints (see Figure 3).
Assembly temperature
increases

Assembly temperature
decreases
Stress is applied tothe solder joint.

The LED and PCB expand at different rates

The LED and PCB contract at different rates

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 theflow of electrical current supplied to the LED, the LED will fail to illuminate (see Figure 4).
A solder crack
occurs in thesolder joint.

A solder crack grows
and the LED fails toilluminate.

Figure 4. How Solder Cracks Occur
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
4/19
Jul. 31, 2023

Application Note
4. Reducing the Occurrence of Solder Cracks
4.1 Effect of the Difference in the CTE between the Package of the LED and the PCB
Solder cracks are more likely to occur when the difference in the CTE between the package of the
LED and the PCB is large. The CTE describes how the size of an object changes with an increasein temperature per degree of Celsius (i.e., /°C). Table 2 shows the package materials used in Nichia
LEDs. Table 3 below shows the CTEs of the package materials of the Nichia LEDs and the CTEsof typical PCB materials. The CTEs listed in the tables are only the typical values of the materials.

Light Emitting Diode

Table 2. Package Materials Used in Nichia LEDs
Package of the LED

LED Series

Aluminum Nitride

Nichia 121, 131, 170, 270 Series LEDs

Aluminum Oxide

Nichia 123, 172 Series LEDs

Resin

Nichia 046, 063, 064, 088, 093, 129, 146, 193, 313, 438, 572 Series LEDs

Table 3. CTEs of the Package Materials of the Nichia LEDs and Typical PCB Materials
PCB

Package of the LED
Material

CTE (1/°C)

Aluminum Nitride

5×10-6

Aluminum Oxide

7×10-6Resin

16×10-6

Material

CTE (1/°C)

Ceramic

8×10-6Iron

12×10-6

Glass Epoxy (FR-4)

14×10-6

Copper17×10-6

Aluminum

21×10-6

Solder cracks can be reduced by selecting a PCB that has a small difference in CTE between the
package material of the LED and the PCB material. For example, the difference in CTE between
Nichia 121, 131, 170, 270 series LEDs that use aluminum nitride for the package material and thealuminum-core PCB is 16×10-6/℃. On the other hand, the difference in CTE between those 121,
131, 170, 270 series LEDs and the copper-core PCB is 12×10-6/℃. This indicates that solder cracks
are less likely to occur when using a copper-core PCB for Nichia 121, 131, 170, 270 series LEDs(see Figure 5).

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
5/19
Jul. 31, 2023

to occur.
20
15
10

Small

5
0

Light Emitting Diode

Nichia 121、131、170、270 series LEDs

25

Solder cracks are likely to occur.

20(×10-6/℃)

Solder cracks are less likely

Coefficient of Thermal Expansion (CTE)25(×10-6/℃)

Coefficient of Thermal Expansion (CTE)

Application Note

15

Large
10
5
0

Copper-core PCB

Nichia 121、131、 Aluminum-core PCB
170、270 series LEDs

Figure 5. Difference in CTE between Nichia 121, 131, 170, 270 series LEDs
and the Two Different Types of PCBs

4.2 Elastic Modulus of the Insulating Layer of the PCB
In general, the use of a PCB containing an insulating layer with a low elastic modulus is effective
in reducing solder cracks. An insulating layer with a low elastic modulus can deform to follow thestress 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).
Expansion
An insulating layer with a low
elastic modulus can reduce stressContraction

LED

applied to the solder joints.
Copper Layer
An insulating layer with a low
elastic modulus
Aluminum-core PCB

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

Note that the use of an aluminum-core PCB containing an insulating layer with a low elastic modulus
may have a low thermal conductivity. Take this into consideration when selecting a PCB for the
chosen application.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
6/19
Jul. 31, 2023

Application Note
4.3 PCB Soldering Pad Patterns
There are two types of soldering pad patterns: Solder Mask Defined (SMD) and Non-Solder Mask
Defined (NSMD). For SMD, the shape and location of the soldering pad pattern are defined by theaperture and location of the solder resist. For NSMD, the shape and location of the soldering padpattern are defined by the shape and location of the copper layer (i.e., the solder resist does notoverlap the copper layer).

Light Emitting DiodeAs shown with the LED-mounted PCBs in Table 4, the SMD pads have the solder joint areas only
on the top of the soldering pad pattern (copper layer). On the other hand, the NSMD pads have thesolder joint areas not only on the top of the soldering pad pattern (copper layer) but also on the sidesof the soldering pad pattern. This indicates that the NSMD pad pattern produces a more reliable
solder joint than SMD pads and has a higher resistance against solder cracks.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
7/19
Jul. 31, 2023

Application Note
Table 4. PCB Pad Patterns (SMD and NSMD Pads)
Pad Pattern

SMD

Solder Resist

NSMD

Copper Layer

Copper Layer

Solder Resist

PCB
Base Metal

Base Metal

Light Emitting Diode

Insulating Layer

Insulating Layer

LED

LED
Solder

Solder

LED-mounted PCB

CopperLayer

Appearances of Soldering
Pad Pattern(Examples)

FeaturesCopperLayer

SolderResistSolderResistSolder Joint
Strength-

Higher than SMD Pads

Solderability

Harder to reduce solder voids andsolder balls

Easier to reduce solder voids andsolder balls

Not good (Solder Resist Printing)Good (Copper Layer Etching)

Better than NSMD Pads due to theLarge Copper Layer-

Accuracy ofSoldering Pad
Pattern
Heat
Dissipation

When selecting a PCB, take the above features into consideration and perform sufficientverifications on the required properties including solder crack resistance.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
8/19
Jul. 31, 2023

Application Note
4.4 Solder Crack ResistanceHigh reliability lead-free solder pastes, which have been specially developed to reduce the risks ofoccurrence and progression of solder cracks, are available.
Generally, the use of high reliability lead-free solder pastes can improve solder joint strength anddelay the occurrence of solder cracks when compared with a standard lead-free solder paste.

Light Emitting Diode

Solder wettability and the amount of solder voids etc. can vary by changing the type of solder paste
used. When selecting a solder paste, ensure that there are no issues with the LED-mounted PCB
assembled in the chosen application prior to use. If any issue is found, adjust the reflow conditions
and optimize the amount of the solder applied etc. to solve the issue.

4.5 Effects of Solder Voids
If a solder crack occurs in a solder joint where many solder voids exist, the growth of the solder
crack can accelerate. When mounting LEDs on PCBs, take measures to reduce solder voids.
Examples of measures to reduce solder voids are as follows:-

Use a PCB with NSMD pads
NSMD pad configuration allows gases in the soldered joint areas and gases/flux residues within
the solder to be easily released to the outside air during reflow soldering (see Table 4 in Section
4.3).

-

Adjust the reflow profile
As a specific measure, gas generation can be reduced by slowing down the pre-heating speed
and/or the reflow heating speed; another example is extending the reflow peak time byincreasing the reflow peak temperature so that the molten condition of the solder can be kept
longer, releasing gases and flux residues to the outside air.
If the pre-heating temperature is toohigh or the pre-heating time is too
long, the flux will deteriorate and thesolder wettability will become poor,
leading to an increase in the amountof solder voids.
Note that adjustment of the reflow
profile should be done within both
Nichia’s
recommended
reflowconditions and the reflow conditionsof the solder used.

Reflow

Temperature

Pre-Heating

Time

Figure 7. Reflow Profile

For Nichia’s recommended reflow conditions, refer to the applicable specification.
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
9/19
Jul. 31, 2023

Application Note
5. Solder Crack Evaluation
Nichia conducted solder crack evaluations using Nichia NCSW170G LEDs. This Nichia LED waschosen for the evaluations since it is one of the products from the Nichia 131/170 series LEDs thathas an operating temperature range between -40℃ to 135℃ (see Figure 8). Note that the solder
crack evaluation results are only reference data based on Nichia’s test conditions.

Note: The soldering pad pattern and metal solder

1.8

EmissionArea

stencil aperture recommended in the specification
are used in the solder crack evaluation.

0.75

1.45

R0.0750.3

R0.075

1.6

Electrode

1.34

1.21

Soldering Pad PatternMetal Solder Stencil Aperture

1.23
NCSW170G LED

0.43

1.7

0.3

1.6

Light Emitting Diode(Unit: mm)

Figure 8. Dimensions Detailed in the Specification
Nichia mounted the NCSW170G LEDs on PCBs under the different conditions shown below andconducted a thermal shock test (temperature range: -40℃ to 135℃) on the LED-mounted PCBs toinvestigate the increase rate in the forward voltage (⊿VF)2 and the lighting failure3 rate. In thistest, evaluations were conducted on different evaluation samples by changing the combination of
the PCB base metal, PCB insulating layer, soldering pad pattern, and solder paste used (see Table
5).
Test Conditions:
LED Part No.:NCSW170G

PCB:

Aluminum-core PCBs containing different types of insulating layers anda copper-core PCB containing a standard insulating layer (see Table 6)

Thickness:

Base metal 1.5mm, insulating layer 100µm, copper layer: 70µm

2When solder cracks occur in an LED, the electrical resistance at the solder joints becomes large and the forward voltage (VF) tends
to increase; the VF is used as a reference value for occurrence of solder cracks. The increase rate of the forward voltage (⊿VF)
represents in percentage how much of VF increases from the initial VF.

3

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-C2-210154-4
10/19
Jul. 31, 2023

Application Note
Soldering Pad Pattern:

SMD or NSMD pad pattern (see Table 7)

Solder Paste:

Lead-free solder with different compositions (see Table 8)

Thickness of the Metal Solder Stencil: 100µm (see Figure 8 for the aperture)
Solder Void Percentage:<10% (Percentage of the total area of voids to the solder joint area, theareas are examined by X-ray)

Conditions of the Temperature Cycle: -40℃ (15 min) ⇔ 135℃ (15 min), up to 3,000 cycles, not in operation
Number of LEDs Tested:

10 or 20 LEDs per evaluation condition

Light Emitting DiodeThe evaluation test results are shown in Sections 5.1 to 5.5. The tables in these sections show
comparisons of number of the evaluation samples with ⊿VF≥10%4 and the lighting failure at eachstage up to 3000 cycles. The graphs in these sections show how the lighting failure increases andhow the average ⊿VF, which were obtained from the evaluation samples that did not fail to emit
light, increases as a reference of occurrence timing of solder cracks.
Table 5. Evaluation Samples Prepared Under Different Conditions
PCB
SampleSolder Paste(See Table 8)Base Metal

Insulating Layer(See Table 6)

Soldering Pad Pattern(See Table 7)

1

AluminumStandard

SMD

Standard lead-free solder

2

CopperStandard

SMD

Standard lead-free solder

3

AluminumLow modulus
elasticity

SMD

Standard lead-free solder

4

AluminumStandard

NSMD

Standard lead-free solder

5

AluminumStandard

SMD

High reliability lead-free solder

6

CopperStandard

SMD

High reliability lead-free solder

7

AluminumLow modulus
elasticity

SMD

High reliability lead-free solder

8

AluminumStandard

NSMD

High reliability lead-free solder

Table 6. Insulating Layers

4Insulating Layer

Modulus Elasticity (Storage Modulus) (GPa)Standard

13

Low modulus elasticity

0.16⊿VF≥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-C2-210154-4
11/19
Jul. 31, 2023

Application Note
Table 7. Soldering Pad Patterns
Soldering Pad Pattern
SMD

NSMD
0.3

1.34

1.34
Copper layer
Solder resist aperture

Light Emitting Diode

2.1

1.7

1.7

0.5

0.3

1.74

Table 8. Solder Pastes
Solder Paste

Composition

Standard lead-free solder
High reliability lead-free solder

Sn-3.0Ag-0.5Cu
Sn-3.4Ag-0.7Cu-3.2Bi-3.0Sb-Ni-x

5.1 Comparison of Evaluation Samples with Different PCB Base Metals
Comparisons were made between the evaluation samples that were prepared under the same
conditions except for using different PCB base metals (see Table 9).
As a result, sample 1 using an aluminum-core PCB has a high occurrence of ⊿VF≥10% and a highrate of lighting failure at 1500 cycles. On the other hand, sample 2 using a copper-core PCB has no
occurrences of those even at 3000 cycles (see Table 10). As shown by the average ⊿VF in Figure9, almost no ⊿VF increment occurred in sample 2 up to 2500 cycles.
The findings indicate that when considering the difference in the CTE between the PCB and the
package material (Aluminum Nitride) of the NSWE170G LED, the use of a copper-core PCB ismore effective for reducing solder cracks than the use of an aluminum-core PCB because thedifference in the CTE between them is small.
Table 9. Evaluation Samples Prepared Under Different Conditions
SamplePCB

Solder Paste

Base Metal

Insulating Layer

Soldering Pad Pattern

1

AluminumStandard

SMD

Standard lead-free solder

2

CopperStandard

SMD

Standard lead-free solder

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
12/19
Jul. 31, 2023

Application Note
Table 10. Occurrence Numbers of ⊿VF≥10% and Lighting Failure
Number of Cycles

Judgement

Sample1

2

Criteria

240

560

800

1000

1500

2000

2500

3000

⊿VF≥10%

0/20

0/20

0/20

0/20

3/14

6/11

6/8

6/6

No Light

0/20

0/20

0/20

0/20

6/20

9/20

12/20

14/20

⊿VF≥10%

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

No Light

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

Samples with the Different PCB Base Metals
1490

Sample 1 (Aluminum-core PCB)

80

Sample 2 (Copper-core PCB)

Sample 1 (Aluminum-core PCB)
1270

Average ⊿VF (%)

Lighting Failure Rate (%)

Light Emitting Diode

Samples with the Different PCB Base Metals
100

60
50
40
30

Sample 2 (Copper-core PCB)

10
8
6
4

20

2

10
0

0
0

500

1000

1500
Number of Cycles

2000

2500

3000

0

500

1000

1500

2000

2500

3000

Number of Cycles

Figure 9. Lighting Failure Rate and Average ⊿VF

5.2 Comparison of Evaluation Samples with Different PCB Insulating Layers
Comparisons were made between the evaluation samples that were prepared under the same
conditions except for using different PCB insulating layers for the aluminum-core PCBs (see Table
11).
As a result, sample 3 using an insulating layer with a low elastic modulus has no occurrence of ⊿VF≥10% up to 2500 cycles and has no lighting failure up to 3000 cycles (see Table 12). As shownby the average ⊿VF in Figure 10, sample 3 has approx. 1% ⊿VF increment in average up to 2500
cycles.
The findings indicate that the use of an aluminum-core PCB with an insulating layer with a low
elastic modulus is more effective for reducing solder cracks than the use of an aluminum-core PCB
with a standard insulating layer.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
13/19
Jul. 31, 2023

Application Note
Table 11. Evaluation Samples Prepared Under Different Conditions
SamplePCB

Solder Paste

Base Metal

Insulating Layer

Soldering Pad Pattern

1

AluminumStandard

SMD

Standard lead-free solder

3

AluminumLow modulus
elasticity

SMD

Standard lead-free solder

Table 12. Occurrence Numbers of ⊿VF≥10% and Lighting Failure1

3

Criteria

240

560

800

1000

1500

2000

2500

3000

⊿VF≥10%

0/20

0/20

0/20

0/20

3/14

6/11

6/8

6/6

No Light

0/20

0/20

0/20

0/20

6/20

9/20

12/20

14/20

⊿VF≥10%

0/10

0/10

0/10

0/10

0/10

0/10

0/10

1/10

No Light

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

Samples with the Different PCB Insulating Layers

Samples with the Different PCB Insulating Layers

100

14
Sample 1 (Standard Insulating Layer)

90

Sample 1 (Standard Insulating Layer)

80

Sample 3 (Insulating Layer with a Low Elastic Modulus)

12

70

Average ⊿VF (%)

Lighting Failure Rate (%)

Light Emitting Diode

Number of Cycles

Judgement

Sample

60
50
40
30

Sample 3 (Insulating Layer with a Low
Elastic Modulus)

10
8

6
4

20

2

10
0

0
0

500

1000

1500

Number of Cycles

2000

2500

3000

0

500

1000

1500

2000

2500

3000

Number of Cycles

Figure 10. Lighting Failure Rate and Average ⊿VF

5.3 Comparison of Evaluation Samples with Different PCB Soldering Pad Patterns
Comparisons were made between the evaluation samples that were prepared under the same
conditions except for using different PCB soldering pad patterns for the aluminum-core PCBs (seeTable 13).

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
14/19
Jul. 31, 2023

Application Note
As a result, sample 4 using the NSMD pad pattern has no occurrence of ⊿VF≥10% up to 1500
cycles and has no lighting failure occurred up to 3000 cycles (see Table 14). As shown by the average⊿VF in Figure 11, sample 4 has less than 1% ⊿VF increment in average up to 1500 cycles.
The findings indicate that the use of the NSMD pad pattern for the aluminum-core PCBs is more
effective for reducing solder cracks than the use of the SMD pad pattern for the aluminum-core
PCBs.
Table 13. Evaluation Samples Prepared Under Different Conditions
PCB

Solder Paste

Base Metal

Insulating Layer

Soldering Pad Pattern

1

AluminumStandard

SMD

Standard lead-free solder

4

AluminumStandard

NSMD

Standard lead-free solder

Table 14. Occurrence Numbers of ⊿VF≥10% and Lighting Failure
Sample1

4

Number of Cycles

Judgement
Criteria

240

560

800

1000

1500

2000

2500

3000

⊿VF≥10%

0/20

0/20

0/20

0/20

3/14

6/11

6/8

6/6

No Light

0/20

0/20

0/20

0/20

6/20

9/20

12/20

14/20

⊿VF≥10%

0/10

0/10

0/10

0/10

0/10

4/10

8/10

9/10

No Light

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

Samples with the Different PCB Soldering Pad Patterns

Samples with the Different PCB Soldering Pad Patterns

100

14
Sample 1 (SMD)90

Sample 1 (SMD)80

Sample 4 (NSMD)

1270

Average ⊿VF (%)

Lighting Failure Rate (%)

Light Emitting Diode

Sample

60
50
40
30

Sample 4 (NSMD)

10
8
6
4

20
2

10

0

0
0

500

1000

1500
Number of Cycles

2000

2500

3000

0

500

1000

1500

2000

2500

3000

Number of Cycles

Figure 11. Lighting Failure Rate and Average ⊿VF

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
15/19
Jul. 31, 2023

Application Note
5.4 Comparison of Evaluation Samples with Different Soldering Pastes
Comparisons were made between the evaluation samples that were prepared under the same
conditions except for using different soldering pastes (see Table 15).
As a result, sample 5 using a high reliability lead-free solder paste has neither occurrence of ⊿VF≥10% nor lighting failure up to 1500 cycles (see Table 16). As shown by the average ⊿VF in
Figure 12, sample 5 has less than 1% ⊿VF increment in average up to 1500 cycles.
The findings indicate that the use of a high reliability lead-free solder paste is more effective for
reducing solder cracks than the use of the standard solder paste.
Table 15. Evaluation Samples Prepared Under Different Conditions

Light Emitting Diode

SamplePCB

Solder Paste

Base Metal

Insulating Layer

Soldering Pad Pattern

1

AluminumStandard

SMD

Standard lead-free solder

5

AluminumStandard

SMD

High reliability lead-free solder

Table 16. Occurrence Numbers of ⊿VF≥10% and Lighting Failure
Number of Cycles

Judgement

Sample1

5

Criteria

240

560

800

1000

1500

2000

2500

3000

⊿VF≥10%

0/20

0/20

0/20

0/20

3/14

6/11

6/8

6/6

No Light

0/20

0/20

0/20

0/20

6/20

9/20

12/20

14/20

⊿VF≥10%

0/20

0/20

0/20

0/20

0/20

1/19

7/16

8/13

No Light

0/20

0/20

0/20

0/20

0/20

1/20

4/20

7/20

Samples with the Different Soldering Pastes

Samples with the Different Soldering Pastes

100

14
12

Sample 5 (High Reliability Lead-free Solder Paste)

80
70

Average ⊿VF (%)

Lighting Failure Rate (%)

Sample 1 (Standard Solder Paste)

Sample 1 (Standard Solder Paste)

90

60
50
40

30

Sample 5 (High Reliability Lead-free Solder Paste)

10
8

6
4

20

2

10

0

0
0

500

1000

1500

Number of Cycles

2000

2500

3000

0

500

1000

1500

2000

2500

3000

Number of Cycles

Figure 12. Lighting Failure Rate and Average ⊿VF
This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
16/19
Jul. 31, 2023

Application Note
5.5 Comparison of Evaluation Samples with a High Reliability Lead-free Solder Paste

Light Emitting Diode

Comparisons were made between the evaluation samples that were prepared under the same
conditions except for using different PCB base metals, PCB insulating layers, PCB soldering padpatterns (see Table 17).
As a result, samples 6, 7, and 8 have neither occurrence of ⊿VF≥10% nor lighting failure up to3000 cycles (see Table 18). In those three samples, almost no ⊿VF increment occurred up to 3000
cycles (see the average ⊿VF in Figure 13).
The findings indicate that when the high reliability lead-free solder paste was used in the evaluations,more effective solder crack resistance was achieved by combining each of these measures to reduce
solder cracks (i.e. use of a copper-core PCB, use of insulating layer with a low modulus elasticity,and use of NSMD pad pattern).
Table 17. Evaluation Samples Prepared Under Different Conditions
SamplePCB

Solder Paste

Base Metal

Insulating Layer

Soldering Pad Pattern

5

AluminumStandard

SMD

High reliability lead-free solder

6

CopperStandard

SMD

High reliability lead-free solder

7

AluminumLow modulus
elasticity

SMD

High reliability lead-free solder

8

AluminumStandard

NSMD

High reliability lead-free solder

Table 18. Occurrence Numbers of ⊿VF≥10% and Lighting Failure
Sample5678Number of Cycles

Judgement
Criteria

240

560

800

1000

1500

2000

2500

3000

⊿VF≥10%

0/20

0/20

0/20

0/20

0/20

1/19

7/16

8/13

No Light

0/20

0/20

0/20

0/20

0/20

1/20

4/20

7/20

⊿VF≥10%

0/20

0/20

0/20

0/20

0/20

0/20

0/20

0/20

No Light

0/20

0/20

0/20

0/20

0/20

0/20

0/20

0/20

⊿VF≥10%

0/20

0/20

0/20

0/20

0/20

0/20

0/20

0/20

No Light

0/20

0/20

0/20

0/20

0/20

0/20

0/20

0/20

⊿VF≥10%

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

No Light

0/10

0/10

0/10

0/10

0/10

0/10

0/10

0/10

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
17/19
Jul. 31, 2023

Application Note

Samples with the High Reliability Lead-free Solder

Samples with the High Reliability Lead-free Solder
14

90

Sample 5

80

Sample 670

Sample 5
12
Sample 6

Sample 7

60

Average ⊿VF (%)

Lighting Failure Rate (%)

100

Sample 8

50
40
30

10

Sample 78

Sample 8

6
4

20

2

10
0

0
0

500

1000

1500

Light Emitting Diode

Number of Cycles

2000

2500

3000

0

500

1000

1500

2000

2500

3000

Number of Cycles

Figure 13. Lighting Failure Rate and Average ⊿VF

6. Summary
When an LED is mounted on a PCB by using solder, especially when the package of the LED is
made of ceramics (aluminum nitride or aluminum oxide), care should be taken because solder cracks
are likely to occur and to grow when the LED-mounted PCB is repeatedly turned on and off underoperating conditions that lead to a large temperature difference and/or in an environment where thetemperature fluctuates significantly.
As examples of measures to reduce solder cracks, this application note explains the selection of a
PCB material considering thermal expansion (CTE), use of an aluminum-core PCBs containing a
low modulus elasticity insulating layer, use of a PCB with NSMD pads, and use of a high reliability
lead-free solder. The solder crack evaluation results in this application note are only reference data
based on Nichia’s test conditions. Before using LEDs, sufficient solder crack evaluations must be
performed by using the PCB and solder pastes that are used for the chosen application withconsideration of conditions/environments in which the LED will actually be used.
A cross-sectional observation of the solder joints and a solder joint strength evaluation (e.g. shear
test) etc. are also effective to evaluate solder cracks.
The measures to reduce solder cracks stated in this application note may affect the heat dissipation
and/or solderability. Moreover, the LED characteristics and reliability may be adversely affected
depending on the materials used.
A light-up test, sufficient verifications etc. of the chosen application must be performed prior to use
under the conditions/environments in which the LED will actually be used to ensure that the
expected performance is maintained.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-210154-4
18/19
Jul. 31, 2023

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-C2-210154-4
19/19
Jul. 31, 2023