Application Note

Light Emitting Diode

LED Mounting Process Techniques for
Full-color RGB SMD LEDs with a Lens

Table of contents
1. Overview ........................................................... 2
2. Applicable Part Numbers .................................. 2
3. Mounting Process Preparation .......................... 2
4. Solder Printing .................................................. 5
5. LED Mounting .................................................. 6
6. Reflow ............................................................... 9
7. Inspection .......................................................... 9
8. Precautions for Assembled PCBs .................... 10
9. Summary ......................................................... 10The Nichia part numbers NSSM137A and NSSM237B within this document are merely Nichia’spart numbers for those Nichia products and are not related nor bear resemblance to any othercompany’s product that might bear a trademark.
This document contains tentative information, Nichia may change the contents without notice.
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1/11Jul. 2024

Application Note
1. Overview
Nichia’s full-color RGB SMD LEDs with a lens are designed to be mounted using a pick-and-placemachine. However, depending on the operation conditions set for the machine or how the LEDs arehandled during the mounting process, failures of the LEDs (i.e. damage to the LED, reliability issues,etc.) or mounting errors may occur.
This application note provides considerations/precautions for the mounting process of the Nichia’s
full-color RGB SMD LEDs with a lens.

2. Applicable Part Numbers

Light Emitting Diode

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

NSSM137A

NSSM237B

5.3×4.24×1.95

5.3×4.24×2.25

Example ofPackage
Appearance
Package Size(Unit: mm)

3. Mounting Process Preparation
PreparationSolderPrinting

Mounting

Reflow

Inspection

3.1 Reel and Embossed Carrier Tape Specifications
The LEDs are delivered in an embossed carrier tape and a reel as shown in Figure 1. The detailed
specifications of the embossed carrier tape are available in the applicable specification for each LEDpart number.

Figure 1. Reel and Embossed Carrier Tape
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Application Note
3.2 Prevention of Moisture Absorption
The reel of the LEDs is sealed in a moisture-proof aluminum bag as shown in Figure 2. If thepackage absorbs moisture and is exposed to heat during soldering, it may cause the moisture tovaporize and the package to expand and the resulting pressure may cause internal delamination (seeFigure 3). This may cause the optical characteristics to degrade. To minimize moisture absorption
in storage/transit, moisture-proof aluminum bags are used for the LEDs with a silica gel packet toabsorb any air moisture in the bag.
Label
Reel
Desiccants

Nxxxxxxx*******

LOT:
QTY.:

YMxxxx-RRR
PCS
RoHS

NICHIA CORPORATION 491 OKA, KAMINAKA, ANAN, TOKUSHIMA, JAPAN

Seal

Light Emitting Diode

XXXX LED
PART NO.:

The LED package
absorbs moisture.

Heat during soldering
causes the moisture tovaporize resulting in thepackage expanding.

Internal delamination occurs
causing adverse effect on theoptical characteristics of the LED.

Moisture-proof Bag

Figure 2. Moisture-Proof Aluminum Bag

Figure 3. Schematic Diagram of LED’s
Moisture Absorption and Vapor
Expansion of the Moisture

3.3 Storage of the LEDs
Table 2 provides the required storage conditions before and after opening the moisture-proofaluminum bag.
Table 2. Storage Conditions
Conditions

Temperature

Humidity

Storage Time

Before Opening the Moisture-proof
Aluminum Bag≤30℃≤90%RHWithin 1 Year from Delivery Date

After Opening the Moisture-proof
Aluminum Bag≤30℃≤70%RH

MSL4

Within 72 Hours

The “After Opening” storage time is different depending on the Moisture Sensitivity Level (MSL)1of the LED. Refer to the specification for each LED part number for the MSL to ensure that soldering
is completed within the specified storage time.
To store any remaining unused LEDs, use a hermetically sealed container with silica gel desiccants.
Nichia recommends placing them back to the original moisture-proof aluminum bag and reseal it.
If the storage time has been exceeded for the LEDs whose “After Opening” storage time is 72 hours,
ensure that the LEDs are baked for ≥24 hours at a temperature of 65±5ºC before use. If any pinksilica gel beads are found within the storage times (see Figure 4), ensure that the LEDs are baked in
the same manner. Baking should only be done once.
Note:
1

Refer to IPC/JEDEC STD-020 for detailed information regarding the MSL.
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Application Note

The blue silica gel beads absorbed
moisture and turned pink.
B. After being left for 168 hours at
30ºC and 70%RH

A. When packed forshipment

Figure 4. Appearance of Silica Gel DesiccantsLight Emitting Diode

When baking the LEDs, remove the reel of the LEDs from the storage container (e.g. a moistureproof aluminum bag). See Figure 5.

Figure 5. Example for Baking the LEDs
If the LEDs are stored in a high temperature environment (≥70℃) for a long period of time, theresin portion of the LED may stick to the top cover tape, causing pick-up errors; storing the LEDs
in this manner may also cause deformation of the embossed carrier tape.
Do not store the LEDs in a manner where excessive external force may be applied to the reel (e.g.
the reel is stored using a vacuum seal, heavy objects are stacked onto the reel, etc.) since it may
cause the embossed carrier tape to deform; see Figure 6. If the embossed carrier tape deforms, theLEDs inside the pockets of the embossed carrier tape may tilt, causing damage to the LEDs and/orpick-up errors.

Correct

Incorrect
Deformed

Deformed

Tilted LED in Pocket

Before Opening theBag with a Reel in it

Squashed Reel as a Resultof Excessive Vacuum Sealing

Figure 6. Correct/Incorrect Examples for Embossed Carrier Tape after Vacuum Sealing

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Application Note
4. Solder Printing
SolderPrinting

Preparation

Mounting

Reflow

Inspection

If the LED is not mounted onto a PCB with an appropriate amount and shape of solder paste, theexpected characteristics of the LED may not be obtained. In order to maintain the amount/shape ofsolder paste in the printing process, the soldering pad pattern and metal solder stencil aperture
pattern should be optimized as well as the printing conditions, and the solder paste must be preparedproperly prior to use.

The solder paste needs to be stirred before use. The purpose of the stir is to restore the even
distribution of solder particles and flux that became uneven due to storage. If the solder paste is notmixed evenly, it interferes with the rolling performance, leading to an inappropriate amount/shapeof the solder when printed on the PCB.
The stirring duration is determined based on the solder paste manufacturer’s recommendation.
4.2 Soldering Pad Pattern and Metal Solder Stencil Aperture Pattern
The figures below show the recommended soldering pad pattern and metal solder stencil aperture
pattern.

0.8
0.8

0.8

0.8

3.96

0.8

● Recommended Metal Solder Stencil Aperture

0.8● Recommended Soldering Pad Pattern

3.96

Light Emitting Diode

4.1 Preparations for Solder Paste1.151.15
5.24

1.15

1.15
5.24

(Unit: mm)

Figure 7. Soldering Pad Pattern and Metal Solder Stencil Aperture Pattern(単位 Unit : mm)

4.3 Printing Condition Adjustment
Adjust the squeegee conditions and the metal solder stencil separation conditions to print with thecorrect amount and shape. The speed, pressing pressure, and angle of the squeegee affect the amountand condition of the solder paste filling the metal solder stencil aperture. Additionally, the speed of
the separation and the distance affects how the shape of the solder on the PCB stays consistent witheach use. These are also affected by the thickness of the metal solder stencil, the aperture pattern,
and the surface roughness of the aperture wall.
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Application Note
In order to prevent the occurrence of solder bridges, etc. and maintain optimal printing conditions,adjust the cleaning method, conditions, and frequency of the metal solder stencil.
Adjust the printing conditions to obtain an appropriate solder shape (see Figures 8 and 9 forexamples). In order to ensure that the appropriate amount of solder paste is applied to the solderingpads consistently, verify the amount of the solder paste by conducting an appearance inspection after
the solder printing and/or an X-ray examination after the LED is mounted.
If the solder printing process is carried out continuously for a long period of time, the viscosity ofthe solder paste may increase, leading to printing failures due to clogging of the metal solder stencil
aperture and poor release of the solder paste. To maintain an appropriate solder shape duringcontinuous operation, it is important to check the solder stencil apertures for clogging and check theviscosity of the solder paste whenever appropriate.

Incorrect

Light Emitting DiodeCorrect

PrintingPrinting

Metal Stencil
PCB

Good Filling of Solder Paste

Insufficient Filling of Solder Paste

under Appropriate Conditions

due to Fast Squeegee Speed

Figure 8. Squeegee Speed and Solder Paste Filling in the Metal Solder Stencil Aperture
Fast Stencil Removal

Incorrect

Appropriate Speed

Correct

Slow Stencil Removal

Incorrect

Figure 9. Speed of Solder Stencil Removal and Shape of the Solder Paste

5. LED Mounting
Preparation

SolderPrinting

Mounting

Reflow

Inspection

If the parameter settings for the pick-and-place machine and the mounting conditions areinappropriate, it may cause issues such as the LEDs falling out of the embossed carrier tape pocket
or sticking to the top cover tape, pick-up errors, poor precision of the placement position, and/or
damage to the LEDs. This section provides the precautions for the LED mounting process that uses
a pick-and-place machine and what measures to be taken when an LED pick-up/placement error
occurs.
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6/11
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Application Note
5.1 Recommended Nozzle
If excessive force is applied to the emitting surface of the LED, it may be damaged, which may
affect the performance/reliability of the LED. Nichia recommends using a nozzle specificallydesigned for the LEDs. Nichia recommends the inner diameter of the nozzle tip should be round(see Figure 10). Additionally, if the tip of the nozzle has burrs, chipping, or foreign substances, theemitting surface may be damaged or contaminated. Ensure that the tip of the nozzle is cleaned before
starting the pick-and-place operations.

4-R0.5

1.8

R processing
1.4

Light Emitting Diode1(Unit: mm)

23

Figure 10. Recommended Nozzle
5.2 Pick-up Position
When setting the LED pick-up position, ensure that the center of the nozzle and the center of theemitting area of the LED are aligned (see Figure 11). If the nozzle picks up the LED at an edge ofthe emitting area, this may damage the emitting surface (i.e. chip, crack, etc.).
Correct

Incorrect

Incorrect

Correct

Nozzle Tip

NSSM137A

NSSM237B

Figure 11. Nozzle Position for LED Pick-up

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Application Note
5.3 LED Pick-up
The recommended LED pick-up operation is to lower the nozzle slowly with suction. The nozzle
should not come into contact with the LEDs. Refer to the outline dimensions of the embossed carrier
tape and the LED detailed in the applicable specification for each LED part number to determine
the nozzle height.
If the pick-up operation is unstable, adjust the nozzle height appropriate for the pick-and-placemachine being used.

NozzleLight Emitting DiodeLower slowly with suction

Embossed Carrier Tape
LEDFigure 12. Recommended LED Pick-up Operation
5.4 LED Placement
When placing the LED on the PCB, the nozzle should further press the LED 0.2mm onto the PCB
from the height where the LED first touches the solder paste (see Figure 13). If the placement depthof the nozzle is insufficient, the LED may float or shift after reflow. If the placement depth is toolarge, an excessive pressure may be applied to the LED resulting in the emitting surface being
damaged and/or solder balls may occur.
The placement pressure changes if there is a warpage in the PCB; verify that the operation conditions
do not cause damage to the LED in the actual mounting process before starting the operation.
Nozzle
LEDPlacement Depth:0.2mm
PCB
Figure 13. Recommended Nozzle Height for Placement Operation

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Application Note
5.5 Rewinding of a Tape on a Reel
To rewind the embossed carrier tape when the operation is interrupted, the force applied must be≤10N to the embossed carrier tape. Otherwise, the LED may stick to the top cover tape and/or theembossed carrier tape pocket may be deformed resulting in the LED being damaged.

6. Reflow
Preparation

SolderPrinting

Mounting

Reflow

Inspection

Light Emitting Diode

6.1 Reflow Conditions
Figure 14 shows the Nichia recommended reflow soldering conditions provided in the applicablespecification for each LED part number; use the recommended reflow conditions specified by themanufacturer of the solder paste being used if it works better for the chosen application.
Additionally, Nichia recommends using a nitrogen reflow atmosphere (O2 concentration: <500ppm).
If the reflow is performed with an air atmosphere, the heat and atmosphere in the reflow oven may
cause the optical characteristics of the LED to degrade.
Note that reflow soldering must not be performed more than twice.
When cooling the LEDs from the peaktemperature, a gradual cooling slope isrecommended; do not cool the LEDs rapidly.
Use the cooling rate of 1.5 to 2℃/sec. forreference. If the components mounted on thePCB are damaged and/or the solder joint
strength is insufficient, the conditions should
be adjusted.

Figure 14. Reflow Soldering Condition (Lead-free Solder)

7. Inspection
Preparation

SolderPrinting

MountingFailure

ReflowInspection

7.1 Lighting Inspection
The lighting inspection is performed either visually or using an automatic imaging inspection system
to check if all the LEDs emit light without issues.

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Application Note
7.1.1 Lighting Inspection Considerations
In order to prevent the LEDs from being damaged during the lighting inspection, operate the LEDs
at a constant current and ensure that the voltage being applied is appropriate for the chosen circuitof the PCB and that the current being applied is small enough (e.g. 1mA per LED).
Additionally, ensure that a hot-wire connection2 of the probes, etc. is not done during the lighting
inspection; if the chosen voltage and current are not appropriate, a large current exceeding theabsolute maximum rating current3 may temporarily flow through the LEDs due to the inrush current
causing damage to the LEDs.

Light Emitting Diode

7.2 Appearance InspectionAn appearance inspection should be performed visually or using an automatic imaging inspection
system to check if there are any abnormalities in appearance (e.g. misalignment/floating of the LED,solder balls, damage to the LED, etc.).
7.3 X-Ray Examination
An X-ray examination should be performed to check if the solder wettability is sufficient and/or if
there are any solder voids, solder balls, etc.

8. Precautions for Assembled PCBs
When handling the assembled PCBs, ensure that the following precautions are followed.
 Do not stack assembled PCBs together. Otherwise, it may cause damage to the emitting area and/or
the resin (e.g. cut, scratch, chip, crack, etc.) and have an effect on the optical characteristics and/or
the reliability.
 If the LEDs are soldered to a PCB and the PCB assembly is bent (e.g. PCB depaneling process),
it may cause the LED package to break. To separate a PCB populated with the LEDs, use a
specially designed tool. Do not break the PCB by hand; this may cause excessive stress to beapplied to the LEDs.

9. Summary
The occurrence of mounting failures for the LED mounting process may vary depending on various
factors including the work environments, equipment, conditions of the materials being used, etc.
Ensure that there are no issues with the mounting operations by performing a mounting test, etc.
before starting the operations.
Note:
2

A hot-wire connection means a test voltage is applied to the PCB with probes, etc. while the power is on.

3

Absolute maximum ratings of the LEDs are the maximum values that must not be exceeded even for a shortperiod of time. For the absolute maximum rating values for each LED, refer to the applicable specification.
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10/11Jul. 2024

Application NoteDisclaimer
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 chosenapplication.

Light Emitting Diode・ The information/data contained herein are only typical examples of performances and/orapplications 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

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