Application Note

Light Emitting Diode

Assembly Precautions for the Nichia
NCSxE17A or NVSxE21A Series LEDs

Table of contents
1. Overview .................................................................. 2
2. Nichia E17/E21 Series .......................................... 2
3. Handling Precautions .......................................... 3
4. Designing a Board and Solder Stencil ........... 4
5. Solder Printing Process ..................................... 13
6. LED Assembly Process ...................................... 15
7. Reflow Process ..................................................... 18
8. Inspection after Reflow ..................................... 19
9. Summary ................................................................ 19

The part number NCSxE17A, NVSxE21A in this document are the part numberof our products, and do not have any relevance or similarity to other companies'
products that may have trademark rights.

This document contains tentative information, Nichia may change the contents without notice.
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Application Note
1. Overview
As a result of growing trends to reduce the size and increase the light energy of LED-based luminaries,
the demand for compact, high luminous flux and high efficiency LEDs has been increasing. Nichia’s
NCSxE17A/NVSxE21A (hereinafter referred to as “E17/E21 Series”) LEDs have a more compact size whencompared to other LEDs that produce the same wattage, this allows for more flexibility for the LED
luminaire design. On the other hand, E17/E21 Series requires more precision/technique regarding themounting accuracy due to its smaller package size.
This application note provides the information on handling and processing, and the results of an assembly
evaluation Nichia conducted.

2. Nichia E17/E21 Series
the luminous efficacy of the LED. The LED does not use a primary
substrate (e.g. lead frame, etc.) for the electrical connection, so the LED
is able to be soldered directly onto a secondary substrate (a print circuitboard) and can have lower thermal resistance. As a result of this, theE17/E21 Series is suitable for luminaires that require high luminous flux

Figure 1. E17/E21 Series

and high density mounting.
This compact package has both drawbacks and advantages, especially

蛍光体
Phosphor sheet
ダイス
LED die
端子 padElectricalin regards to the assembly difficulty. The small size of the electrical pads,
the fact that the electrical pads are located around center of rear of the
package which can cause not to create a solder fillet, and that electricalpads are closer in proximity to each other, make this LED more difficult

Figure 2. Structure

to assemble than the conventional LED package sizes.
1.7

0.27～0.35

0.86

1.7

2- 0.86

0.2

AnodeCathode
2- 0.33[Unit：mm]

Figure 3. Outline Dimensions of NCSxE17A
2.1

0.27～0.35

1.26

2- 1.260.2

2.1

Light Emitting DiodeE17/E21 Series has a compact package and a structure that maximizes

Cathode Anode2- 0.53[Unit：mm]

Figure 4. Outline Dimensions of NVSxE21A
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Application Note
3. Handling Precautions
Since the E17/E21 Series is a thin package with no submount in its structure is more sensitive to external
stress and force. The LED also is not equipped with an ESD protection device (e.g. zener diode). Additionalcare should be taken to avoid external stress/force and ESD damage.
3.1. Force (when loading)
When a nozzle is used during the assembly process, nomore than 5N of force should be applied to the LED.
Recommended conditions for a nozzle and force areprovided in Section 6.
Figure 5. LED damaged by excessive press force
3.2. Bare hands

Light Emitting Diode

Handling the LED with bare hands will contaminate the LED surface and may affect the opticalcharacteristics: it might cause the LED to be deformed and/or the bump to break, which will cause the
LED not to illuminate.
ESD damage to the die may happen since no ESD protection device is included the LED. Do not handle
the LED with bare hands.
3.3. Tweezers
The silicone resin used in the LED is soft. Applying force with tweezers may cause the resin to be damaged
and the LED not to illuminate the same as if the LED has been handled with bare hands do. Do not use
tweezers to handle the LED.
3.4. Electrostatic Discharge (ESD)
LED is not equipped with a protection device. When handling the LED, measures against electrostatic
discharge such as using an ESD mat made of conductive materials and an ionizer are strongly
recommended at every assembly process.
Mounting a protection device such as zener diode on the PCB is recommended to protect from ESD.
3.5. Stack assembled PCBs
Since the resin used in the LED is soft, do not stack assembled

Incorrect

PCBs together. Failure to comply can cause the resin portionof the product to be cut, chipped, delaminated and/or
deformed. This also applies to how the assembled PCBs arepacked as the same failure may occur.
Figure 6. Improper storage of assembled PCBs
3.6. Hand soldering
The electrical pads are hidden on the back side of the LED, so hand soldering is not possible to perform.
Using a hot plate is also not recommended as it would not be possible to confirm the position of theelectrical pads and this may cause a short and/or open failure mode. These types of soldering are notrecommended.

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Application Note
3.7. Repairing
As explained in section 3.6, do not repair and/or rework the LED. Do not manually mount LED onto the
PCB even if reflow soldering will be performed. This may cause the LED to have an open and/or short
failure mode.

4. Designing a Board and Solder Stencil
Small electrical pads and the close proximity of the electrical pads on the LED affect the accuracy of the
PCB design, creating the solder stencil design, and solder mask. Additionally, the PCB design and material
selection are critical for thermal dissipation management.
This section provides tips for PCB design and results of an assembly evaluation.

Light Emitting Diode4.1. Conditions for the pad pattern and stencil
Table 1. NCSxE17A recommended soldering pad pattern and solder stencil

NCSxE17A
LED

Soldering Pad Pattern
Solder Mask

Stencil Aperture

Thickness of the stencil: 100 μm
ランドパターン
Solder pad pattern
Solder mask aperture
ソルダーレジスト開口部
Solder stencil aperture
メタルマスク開口部

Table 2. NVSxE21A recommended soldering pad pattern and solder stencil

NVSxE21A
LED

Soldering Pad Pattern
Solder Mask

Stencil Aperture

Thickness of the stencil: 100 μm
ランドパターン
Solder pad pattern
Solder mask aperture
ソルダーレジスト開口部
Solder stencil aperture
メタルマスク開口部

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Application Note
4.2. PCB materials
Composite epoxy materials (CEM-3), glass fiber epoxy laminate (FR-4), metal (e.g. aluminum) arecommonly used as PCB materials. Metal-core PCBs have good thermal conductivity and heat dissipation,
and are recommended if E17/E21 Series is used with high density mounting.
The application note “NxSxExxA Design Considerations for Direct Mountable Chip LEDs for High-Density
Applications” provides details regarding the high density modules for E17/E21 Series.
4.3. Insulation layer
Heat dissipation for LEDs relies on the PCB material and the thickness of the insulation layer. Selecting theproper insulation layer for each luminaire is advised.
The application note “NxSxExxA Design Considerations for Direct Mountable Chip LEDs for High-Density
Applications” describes the relationship between board thickness and thermal resistance.

Light Emitting Diode4.4. Copper layer
The recommended copper layer for the pad pattern is 35μm.
Etching is a common process to remove the unmasked area. Accuracy of etching is decreased if the copper
layer is thick since the unmasked area is not completely removed by etching.
The small electrical pad area and the narrow space between the electrical pads (200μm) require a proper
solder pad pattern for assembly. If the solder pads are not completely etched, it will cause the LED to havea short or open circuit.
4.5. Solder mask
In PCB design, the method for the solder mask is defined as either Solder Mask Defined (SMD) or NonSolder Mask Defined (NSMD). Each type has pros and cons as shown in Table 3.
In general, using the copper etching solution (Copper defined pad) gives more precision than using thesolder mask printing; therefore, NSMD formed with the copper etching solution is recommended for
E17/E21 Series. SMD has better heat dissipation since SMD is able to provide a larger pad area; however
it may result in a misaligned solder mask, leading to an inaccurate pad pattern, causing assembly failure.

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Application Note
Table 3. Solder mask design

Light Emitting Diode

NSMD

SMD

■ Solder paste■ Solder mask
■ Copper layer■ Insulation layer■ PCB

Assembly
Implementation

Accuracy ofAssembly

Heat
Dissipation-AdvantageReduce solder ball and void occurrence.
-AdvantageMisalignment of the solder mask canbe absorbed.

-DisadvantageSolder mask may overlay the electricalpads due to misalignment of the solder
mask.

-Disadvantage--Advantage-

Poor heat dissipation due to the small

Better heat dissipation due to the large

copper pad area.

copper pad area.

4.6. Solder stencil
The solder stencil aperture of E17/E21 Series is small; as aresult, depending on how the aperture is created there is apotential for clogging of the solder stencil aperture during
the soldering printing process.
Special process for low roughness on surfaces such as
electric polishing and fluorinating is needed for the solder
stencil to improve the solder paste releasing property if

Figure 7. Clogged solder

clogging of the aperture during the solder printing process

stencil aperture

frequently occurs.

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Application Note
4.7. LED mounting pitch
The LED mounting pitch for high-density modules should consider the accuracy of the assembly machine
and the tolerance of the LED package dimensions and electrical pads.
√ 0.1 2 (accuracy of assembly machine) + 0.052 (tolerance of LED package dimensions) + 0.052 (tolerance of electrical pads)= 0.122 (tolerance in single side) ⇒ 0.244 (tolerance in both side) ≅ 0.3mm(Formula 1)
For example, assembly accuracy for an assembly machine such as solder printing and a chip mounter is
0.1mm, the minimum LED pitch will be 0.3mm according to the formula above. To take into consideration
the LED alignment, a LED mounting pitch over 0.4mm is recommended.
4.8. Evaluation results for amount and position of solder paste

Light Emitting DiodeThe area of the solder stencil aperture (amount of solder paste) was evaluated and compared with therecommended solder stencil aperture (specified in section 4.1). The solder mask was made with the NSMD
method.
As shown in tables 4 and 5, both NCSxE17A and NVSxE21A did not have any assembly issue; however as
the solder paste amount increases, the possibility that the LEDs will float on the solder also increases.
In addition, no assembly issues were found in any conditions in regards to the distance between the solder
paste (See tables 6 and 7); however, there are possibilities for LED failure when the solder paste is mounted
to the inward side of an electrical pad (distance of solder paste is short) or to the outward side of anelectrical pad (distance of solder paste is long) from the recommended soldering position.
Solder paste reaches to the other side of the solder paste (electrical pad) when LED is pushed onto thesolder paste if solder paste is mounted the inward side of an electrical pad. This may cause to the LED toshort.
An open failure mode may occur if the LED is not mounted to the proper position if the solder paste ismounted to the outward side of an electrical pad.
The solder stencil aperture should be designed so the solder is printed at the center of each electrical pad.

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Application Note
Table 4. Solder Amount Evaluation (NCSxE17A)

NCSxE17A
0.2mm×0.5mm

0.2mm×0.6mm

0.2mm×0.7mm(vs. Recommendation：-17%)（Recommendation）(vs. Recommendation：+17%)

Solder

K: 34.5%

K: 41.5%

K: 48.6%/Electrical Pad Pattern

A: 50.8%

A: 61.1%

A: 71.5%

Light Emitting Diode

Soldering Position

After Soldering

Xray after Assembly

A

K

A

K

A

K

K

A

K

A

K

A

LED Lifting

Soldering Position

Observation direction for LED Lifting

Pad pattern
ランドパターン
Electrical pad
電極端子
Solder stencil aperture
メタルマスク開口部

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Application Note
Table 5. Solder Amount Evaluation (NVSxE21A)

NVSxE21A
0.35mm×0.65mm

0.35mm×0.80mm

0.35mm×0.95mm(vs. Recommendation：-17%)（Recommendation）(vs. Recommendation：+17%)

Solder

K: 33.6%

K: 41.6%

K: 49.3%/Electrical Pad Pattern

A: 52.9%

A: 65.4%

A: 77.6%

Light Emitting Diode

Soldering Position

After Soldering

Xray after Assembly

A

K

A

K

K

A

K

A

A

K

K

A

LED Lifting

Soldering Position

Observation direction for LED Lifting

Pad pattern
ランドパターン
Electrical pad
電極端子
Solder stencil aperture
メタルマスク開口部

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Application Note
Table 6. Soldering Distance Evaluation (NCSxE17A)

NCSxE17A
Inwardfrom the electrical pads

Centerfrom the electrical pads
（Recommendation）

Outwardfrom the electrical pads

Pad pattern
ランドパターン
Electrical pad
電極端子
メタルマスク開口部
Solder stencil aperture

Soldering

Light Emitting Diode

Position

X-ray after
Assembly

Lighting

Light

Light

Light

Solder Ball

No

No

No

Table 7. Soldering Distance Evaluation (NVSxE21A)

NVSxE21A
Inwardfrom the electrical pads

Centerfrom the electrical pads
（Recommendation）

Outwardfrom the electrical pads

Pad pattern
ランドパターン
Electrical pad
電極端子

Soldering

メタルマスク開口部
Solder stencil aperture

Position

X-ray after
Assembly

Lighting

Light

Light

Light

Solder Ball

No

No

No

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Application Note
4.9. Evaluation results for self-alignment
Self-alignment was evaluated under the condition shown in section 4.8. The solder mask was made with
the NSMD method.
As shown below in Figures 8 to 15, the self-alignment effects more when the amount of solder paste isincreased. At the same time, a larger solder paste volume increases the possibility of the LED floating. As
a result, the self-alignment and the LED float will be a trade-off at a certain amount of solder paste.
Table 8. Test conditions for self-alignment test (NCSxE17A)

SolderPrinting

x: +0.1mm

x: -0.1mm

y: +0.1mm

y: -0.1mm

θ: +2°

θ: +5°LED Mounting
Position
A

K

K

0.10

0.2×0.5
0.2×0.6

0.00

0.2×0.7-0.05

Mount position-0.10

0.2×0.50.05⊿y[mm]

0.05

0.2×0.6

0.00

0.2×0.7-0.05

Mount position

-0.10

-0.10

-0.05

0.00

0.05

0.10

-0.15
-0.15

0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

⊿x[mm]⊿x[mm]

Figure 8. NCSxE17A Test Result (xy+0.1mm)

Figure 9. NCSxE17A Test Result (xy-0.1mm)

8

θ: +2°

8

6

2
0

-2

θ: +5°

6

4

4

0.2×0.5

0.2×0.6
0.2×0.7
Mount position

Θ[°]⊿y[mm]

AK

x: -0.1mm, y: -0.1mm

0.15

0.10

-0.15
-0.15

A

K

A

x: +0.1mm, y: +0.1mm

0.15

Θ[°]

Light Emitting Diode

A

K

Conditions

20-2

0.2×0.5
0.2×0.6
0.2×0.7

Mount position

-4

-4

-6

-6

-8

-8

Figure 10. NCSxE17A Test Result (θ+2o)

Figure 11. NCSxE17A Test Result (θ+5o)This document contains tentative information, Nichia may change the contents without notice.
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Application Note
Table 9. Test conditions for self-alignment test (NVSxE21A)

SolderPrinting

K

Conditions

A

x: +0.1mm

x: -0.1mm

y: +0.1mm

y: -0.1mm

θ: +2°

θ: +5°LED Mounting
PositionAA

K

x: +0.1mm, y: +0.1mm

0.15

0.35×0.65
0.35×0.8

x: -0.1mm, y: -0.1mm

0.00

0.35×0.95-0.05

Mount position

0.35×0.65

0.05⊿y[mm]

0.35×0.8

0.00

0.35×0.95-0.05

Mount position

-0.10

-0.10

-0.10

-0.05

0.00

0.05

0.10

-0.15
-0.15

0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

⊿x[mm]⊿x[mm]

Figure 12. NVSxE21A Test Result (xy+0.1mm)

Figure 13. NVSxE21A Test Result (xy-0.1mm)

8

θ: +2°

8

6

2
0
-2
-4

θ: +5°

6

4

4

0.35×0.65
0.35×0.8
0.35×0.95
Mount position

Θ[°]⊿y[mm]

A

K

0.10

0.05

-0.15
-0.15

A

K

0.15

0.10

Θ[°]

Light Emitting Diode

K

2
0
-2
-4

0.35×0.65
0.35×0.8

0.35×0.95
Mount position

-6

-6

-8

-8

Figure 14. NVSxE21A Test Result (θ+2o)

Figure 15. NVSxE21A Test Result (θ+5o)This document contains tentative information, Nichia may change the contents without notice.
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Application Note
5. Solder Printing Process
Small electrical pads (or solder joint pads) and the close proximity of the electrical pads could lead to amisalignment of the solder paste and may cause the LED to have an open or short failure. The solder
position for the solder printing process is key to prevent this type of failure.
Incorrect

Incorrect

Possible to be short

Possible to be open

Figure 16. Example of improper soldering
5.1. Soldering

Light Emitting DiodeThe recommended particle size for solder powder is less than 30μm taking into consideration the printing
properties of the solder: The particle size is commonly around 1/5 size of the solder stencil aperture andless than 1/3 of the solder stencil thickness.
If the particle size is large, the particle density will be low and may increase the gap between the solder
particles as there may be a larger amount scraped off when using a squeegee; additionally, the amountof the solder paste will be insufficient. If the particle size is small, the relative solder surface area will
increase due to oxidization and this may result in the decrease of the solder ball and the wettability
performance. This can increase the occurrence of an LED failure.
The recommended composition for the solder paste is SAC based (Sn-3.0Ag-0.5Cu) and silver-free(manufacturer: NIHON SUPERIOR, product type: SN100C).
The solder paste enhanced solder joint strength may fail due to the coefficient of the thermal expansion
difference between the solder and the circuit board. This leads to stress to the LED and may cause it tocrack or break.
The solder type and composition of the solder may impact the reliability. An evaluation of both thesolderability and reliability should be performed prior to use to ensure there is no issue with the reliability
for the chosen application.
5.2. Squeegee
Polyurethane rubber or metal are commonly used materials for a squeegee.
If the squeegee’s material is soft (e.g. polyurethane rubber), the tip of the squeegee may deform when
excess pressure is applied and more solder paste will be scraped off by the deformed squeegee. As theresult, the remaining amount of solder paste may be insufficient.
The metal squeegee is recommended when LEDs require high accuracy of assembly, such as the E17/E21
Series models. However, using a metal squeegee increases the wear on the solder stencil more than apolyurethane rubber squeegee.

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Application Note
To prevent misalignment of the LEDs during the solder printing process, the solder stencil needs to be
designed taking into consideration the printing direction as shown in Figure 17. The solder stencil design
must have the electrical pads (anode and cathode) aligned so the long side of the pads are parallel to theprinting direction.
If the printing direction and the long side of the electrical pads are placed perpendicular to each other,
the LEDs may have an open or short since the solder stencil is positioned onto the circuit board
inappropriately.
Squeegee

Solder Paste

Stencil
Aperture

Electrical pads
direction

Light Emitting Diode

Printing direction

Figure 17. Solder printing direction
5.3. Printing speed
As Figure 18 shows, the printing speed of most solder printing machines can be adjusted to take into
consideration the solder printing conditions in the print settings.
The solder paste is not able to get into the solder stencil apertures if the speed is too high. This may cause
solder misalignment and/or an insufficient solder volume.
The printing speed should be adjusted so that it is slow enough to allow the solder paste to roll over thesurface of the solder stencil efficiently.

Figure 18. Image of the print setting
5.4. Printing pressure
The printing pressure can also be adjusted in the print settings.
Excessive solder volume will occur if the printing pressure is too low. Alternately if the pressure is too high,then the solder volume will be insufficient and the wear on the solder stencil and the squeegee isaccelerated which reduces their product lifetime.
The printing pressure should be adjusted to the lowest required level for quality printing performanceand continual printing.
The pressure should also be adjusted as needed for each kind of solder paste, squeegee, and theirconditions since printing conditions will vary.
5.5. Inspection of the solder printing process
A 3D solder paste inspection machine should be installed for solder paste inspection and since the solder
area is small a high resolution camera is also required to ensure measurement accuracy.
There are other failures that were not indicate in the previous sections that may occur during the soldering
process. For these other failures, see Table 10 and Figure 19.
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Application Note
Table 10. Examples of other failure modes during the soldering process
Mode

Cause

Countermeasure

SpreadingWider clearance between PCB

Adjust the height of the stencil(Excessive solder volume)and the solder stencil

Adjust the support device under the PCB

Clogged solder stencil aperture

Clean the solder stencil aperture area
Use a solder stencil that can release thepaste properly

Blurring(Insufficient solder volume)

Dried up solder paste

Check the solder stirring conditions
Control the solder time and frequency ofsoldering

Incorrect

Light Emitting Diode

Incorrect

SpreadBlur

Figure 19. Examples of Soldering Failures

6. LED Assembly Process
Handling precaution at the LED assembly process is described in Section 6. Mounting accuracy is requiredfor LEDs with small package as the soldering printing process does.
6.1. Tape feeder
There are two drive types of tape feeders: electrical (motorized) feeders and mechanical (pneumatic)
feeders.
In general, the motorized feeder has less vibration when the top cover tape is removed, so the LED ispicked up more accurately. If the LED is inclined or popped out so that the pick-and-place nozzle is notable to pick up the LED, the feeder speed should be adjusted to be slower or a motorized feeder with asmaller motor should be used.
If the vibrations are large during operation of the feeder, the LED surface may touch the feeder shutter
and may cause the LED to become damaged, especially when the top cover tape is removed further from
where the nozzle picks up the LED (see Figure 20). Reducing the vibrations or changing the tape removal
position to right next to the pick-and-place nozzle may improve the situation.
トップカバーテープ
Tape 剥離位置
removal position

Pick-and-place nozzle
吸着ノズル

フィーダーカバー
Feedershutter ⇒⇒Topcover tape ⇒⇒トップカバーテープ
Carrier tape ⇒⇒エンボスキャリアテープ

LED吸着位置
LED pick up position
テープ送り方向
Feed direction of the carrier tapeFigure 20. Example of failure during the tape feeding processThis document contains tentative information, Nichia may change the contents without notice.
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Application Note
6.2. Pick-and-place nozzle
Ensure a proper the pick-and-place nozzle should be chosen.
If a nozzle that is an improper size and/or shape is used, a※参考寸法
Dimension (Ref.)[Unit: mm][単位: mm]0.65

pickup failure may occur (e.g. air leakage from the nozzle
causes the LED to tilt during pick-up and the LED surface
becomes scratched). This may affect the LED characteristics(e.g. LED might dim, have a color shift, etc.).

0.65

The shape of generic nozzles may be different depending on

Figure 21. Example ofthe machine manufacturer. The suitable size for the pick-up-

pick-and-place

place nozzle for the E17/E21 Series is 1005/1608.

nozzle6.3. Image recognition and adjustment
Using image recognition and adjusting the pickup position for each LED should be implemented toLight Emitting Diodemaintain assembly accuracy. It is recommended to have the adjustment based on the position of theelectrical pads for higher assembly accuracy.

Figure 22. Image recognition and adjustment during the pick-up-place process
6.4. Height for LED pickup
Recommended height for LED pickup is the same height as top of
the carrier tape.
Nozzle may not be able to pick up the LED or LED may be picked
up incorrectly if pickup height is too high. If the nozzle suction is
too close to the LED surface, LED may get stuck in the carrier tapewhen the nozzle touches and pushes the LED, and/or the LED

Nozzle吸着ノズル

推奨吸着高さRecommended heightsurface may become damaged.
Recommended height for LED pickup varies by LED mounters.
Evaluating the nozzle setup prior assembly should be performed.

Carrier tape
エンボスキャリアテープ

Figure 23. Recommended pickup height
6.5. Pressure during LED mounting
When mounting the LED onto a PCB the recommended height forthe press force is 0.2mm from top of the LED. If the press force is
too weak, the LED may not come in contact with the solder pasteor the LED may lift after the soldering process.

Nozzle
吸着ノズル
Recommended height

to force the pressure
推奨搭載高さ0.2㎜

If press force is too strong, LED surface may damage or solder ball
may appear.

PCB
実装基板

Figure 24. Recommended height to force the pressureThis document contains tentative information, Nichia may change the contents without notice.
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Application Note
6.6. Inspection after the LED mounted
To confirm that the LEDs are mounted in the proper position, it is recommended that right before thesolder process (after the LEDs and surrounding components are mounted onto the PCB) a visualinspection by eyes or by using an image inspection machine is performed.
There are other failures that were not indicate in the previous sections that may occur during the LED
mounting process. For these other failures, see Table 11.
Table 11. Examples of other failure modes during the LED mounting process
Mode

Cause

Countermeasure

LED is not mounted in the proper

Set the pickup position to the center of

positionthe LED.

Misplacement

Insufficient solder paste volume

Check the soldering process(LED is not mounted

PCB warpage

Use backside support for PCB

on the PCB)

Improper PCB thickness

Check the PCB thickness

Incorrect parameter for the mounting

Adjust the parameters for the mounting

positionprogramLight Emitting Diode

Suction error

Misalignment

Poor assembly accuracy

Check PCB design (e.g. pad pattern,solder mask, etc.)

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Application Note
7. Reflow Process
The recommended reflow soldering conditions are shown in Table 12.
If conditions other than those noted in Table 12 would be applied, then it should be based on therecommended conditions of the chosen solder paste. Air flow soldering conditions can cause opticaldegradation, caused by heat and/or atmosphere. Nitrogen reflow soldering is recommended.
Peak Temperature

TemperatureLight Emitting Diode

Pre-Heat

Reflow
Cooling
Time

Figure 25. Reflow profile
Table 12. Reflow profile for E17/E21 Series
Process

Recommended

A faster ramp-up rate increases the potential

Ramp-up rate
Start – Pre-heat

Note

Speed: 1～5℃/sec

Pre-heat - Reflow

occurrence of solder balls and/or the solder paste toslump (e.g. too much heat and the solder paste is too
thin [low viscosity]).
The solvent in the paste begins to evaporate. If the riserate (temperature level) is too low, it increases the

Pre-heat

Temp: 180～200℃

potential occurrence of poor solder wettability and1void. If the pre-heat time is too long, the activation

Time: 90 ～120sec

period of the flux decreases and unmelted solder ismore likely to occur.
The temperature is kept above the melting point of theTemp: 220～260℃

Reflow

1

Time: 30 ～60sec

solder.
If the temperature is not high enough, it may lead to amelting failure (e.g. unmelted solder).
The temperature is kept above the melting point of thePeak temperature

Temp: <260℃

solder.

Time: <10sec

If the temperature is not high enough, it may lead to amelting failure (e.g. unmelted solder).

Cooling rate

1

-1

If the cooling rate is slow, it may cause a decrease in
the strength of the solder joint.

: Recommended condition determined by solder type.

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Application Note
8. Inspection after Reflow
Since the E17/E21 Series is a small package and the electrical pads are hidden on the back side of the LED,
the accuracy of the soldering conditions is not able to be confirmed during the reflow process, so aninspection after the reflow process is important.
The inspection criteria needs to be determined depending on the user’s chosen assembly process andapplication.
The inspection process below describes what items need to be checked for solderability. Evaluation tests
such as reliability tests are needed to ensure the reliability of LED mounted boards or fixtures.
8.1. Lighting inspection
Visual inspection by eyes or using an image inspection machine to verify if the LEDs are lit normally.

Light Emitting Diode8.2. Electrical characteristics inspection
Inspection of the electrical characteristics to determine if the forward current is being applied as designed
and whether the forward voltage value is reasonable in relation to the applied forward current.
8.3. Visual inspection
A visual inspection by eyes or using an image inspection machine to inspect that the LEDs are mounted
properly (e.g. no misalignment, lifting, solder ball, LED damage).
E17/E21 Series is a small package and the electrical pads are hidden on the back side of the LED; so a
visual inspection may not be able to detect soldering failures.
8.4. X ray inspection
An X-ray inspection is used for inspecting the solder wettability, for solder voids, and for solder balls.

Figure 26. Solder ballFigure 27. Poor wettability

9. Summary
E17/E21 Series requires more caution regarding the assembly techniques than conventional LED packages
due to its package size and structure. As a result, the PCB design for E17/E21 Series is important.
If the accuracy of the PCB design is poor, assembly failures may continue to occur even if the assembly
process is reviewed and improved. A receiving inspection of the PCB should be performed to ensure that
PCBs are made as designed.
Although this application note explains precautions and failure modes during the assembly process, theuser is still responsible for evaluating the chosen assembly process and reliability.

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Application Note

Light Emitting Diode

Disclaimer
This application note is a controlled document of Nichia Corporation (Nichia) published toprovide technical information/data for reference purposes only. By using this applicationnote, 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 licenseunder or immunity from any intellectual property rights or other rights held by Nichia or
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NICHIA CORPORATION
http://www.nichia.co.jp

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