Application Note

Light Emitting Diode

LED Mounting Process Techniques
for the Nichia 131 or 170 Series LEDs

Table of contents
1. Overview ......................................................... 2
2. Applicable Part Numbers ................................ 2
3. Mounting Process Preparation ........................ 2
4. Solder Printing ................................................ 5
5. LED Mounting ................................................ 9
6. Reflow ........................................................... 16
7. Mounting Test ............................................... 19
8. Inspection ...................................................... 20
9. Precautions for Assembled PCBs .................. 21
10. Summary ....................................................... 22

The Nichia part numbers NCSx131x, NC2x131x, NCSx170x, NC2x170x, and NJSx170x within
this document are merely Nichia’s part numbers for those Nichia products and are not related norbear resemblance to any other company’s product that might bear a trademark.
This document contains tentative information, Nichia may change the contents without notice.
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Application Note
1. Overview
Nichia’s surface-mount LEDs are designed to be mounted using a pick-and-place machine. However,depending on the operation conditions set for the machine or how the LEDs are handled during themounting 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
131 or 170 Series LEDs.

2. Applicable Part Numbers

Light Emitting Diode

This application note applies to the LEDs shown in Table 1.
Table 1. Applicable LED Part/Series Numbers
Category
Part Number2

Nichia 170 Series1

Nichia 131 Series1
NCSx131xNC2x131x

NCSx170xNC2x170x

NJSx170x

NCSW131G

NC2W131F

NCSW170G

NC2W170G

NJSW170F

1.8×1.45×0.75

3.0×1.6×0.75

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)

3. Mounting Process Preparation
Preparation

SolderPrinting

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.

Note:
1

The electrode pattern on the back of the package for the Nichia 131 Series and Nichia 170 Series is different.

2

The x represents a letter that follows the alphanumeric code of the same LED type.
(Ex: NCSx170x → NCSW170D, NCSW170F, NCSY170F, NCSA170G, NCSW170G, NCSW170G-SA, etc.)
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Application Note
Reel

Embossed Carrier Tape

Φ180+0-3

Trailer and Leader
Top Cover Tape

13+1-0Φ60+1-0

Feed
Direction

Trailer 160mm MIN(Empty Pockets)

Leader with Top Cover Tape
100mm MIN(Empty Pocket)

Loaded Pockets

15.4±1Label

Leader without Top Cover Tape 400mm MIN(Unit: mm)

Figure 1. Reel and Embossed Carrier Tape (Example for the NC2x170x LED)

Light Emitting Diode

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 the
package 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

XXXX LED
PART NO.:

Nxxxxxxx*******

LOT:
QTY.:

YMxxxx-RRR
PCS
RoHS

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

The LED package
absorbs moisture.

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

Internal delamination occurs
causing adverse effect on the
optical 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-proof
aluminum 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%RHMSL2

Within 1 Year

MSL3

Within 168 Hours

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Application Note
The “After Opening” storage time is different depending on the Moisture Sensitivity Level (MSL)3of 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 168
hours, ensure that the LEDs are baked for ≥24 hours at a temperature of 65±5ºC before use. If any
pink silica 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.

Light Emitting DiodeThe blue silica gel beads absorbed
moisture and turned pink.
A. When packed forshipment

B. After being left for 168 hours at
30ºC and 70%RH

Figure 4. Appearance of Silica Gel Desiccants
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.

Note:
3

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

Incorrect

Correct

Light Emitting Diode

Deformed

Deformed

Tilted LED in Pocket

Before Opening the
Bag 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

4. Solder Printing
Preparation

SolderPrinting

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.
4.1 Preparations for Solder Paste
Usually, the solder paste that is stored in a refrigerator cannot be used immediately and needs to be
stirred before use. The purpose of the stir is to restore the even distribution of solder particles andflux that became uneven due to storage in the refrigerator. If the solder paste is not mixed evenly, itinterferes with the rolling performance, leading to an inappropriate amount/shape of the solder whenprinted on the PCB.
The solder paste container should not be opened immediately after taken out from the refrigerator.
Otherwise the solder paste absorbs moisture due to condensation.

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Application Note
Leave the solder paste at room temperature for approximately 60 minutes after taking it out fromthe refrigerator to ensure that it returns to room temperature before stirring. The temperature of thesolder paste will increase if it is stirred for a long time, which deteriorates the flux. Stirring for one
minute may be enough for some kinds of solder paste; determine the stirring duration based on thesolder paste manufacturer’s recommendation. If it is suspected that the temperature of the solder
paste increased in the container after stirring, the stirring duration may have been too long; shorten
the stirring duration.

The figures below show the recommended soldering pad pattern and metal solder stencil aperture
pattern for the NCSx170x LEDs as examples of the patterns used to mount an LED onto a PCB. For
other LED part number patterns, refer to the applicable specification for each LED part number.
● Recommended Soldering Pad Pattern● Recommended Metal Solder Stencil Aperture

1.34
0.3

1.21

R0.0750.43

1.6

R0.075

1.7

Light Emitting Diode4.2 Soldering Pad Pattern and Metal Solder Stencil Aperture Pattern(Unit: mm)(単位 Unit: mm)

Figure 7. Soldering Pad Pattern and Metal Solder Stencil Aperture Pattern
Recommended for the NCSx170x
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.
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). An appearance inspection after solder printing is recommended in order to check if thesolder paste has been printed appropriately.

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Application Note
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

Correct

Printing

Metal Stencil

Printing

Light Emitting Diode

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
4.4 LED Failures Related to Poor Solder Printing
If a metal solder stencil aperture is clogged and/or the conditions of the board separation is not
appropriate, a sufficient amount of the solder paste may not be applied to the PCB. This will lead toinsufficient heat dissipation of the LED causing the junction temperature (TJ) of the LED tosignificantly increase, resulting in a reduction in the luminous flux and/or an adverse effect on thereliability performance. In the worst case, this may cause the circuit to become open causing the
LED not to illuminate due to an electrical connection failure between the LED and the PCB or the
LED to be removed from the PCB. Figure 8 shows examples of the solder printing failures.

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Application Note

Reduction in Luminous Flux
Caused by a significant increase in the TJ
due to insufficient heat dissipation.

a) Solder Printing Failure Resulting in a Reduction in the Luminous Flux of the LED

Open Circuit/LED Removal from the PCB
In some cases, the circuit may become open

Light Emitting Diodeor the LED could be removed from the PCB.

b) Solder Printing Failure Resulting in Open Circuit/LED Removal from the PCB

Figure 10. Examples of the Failures Caused by Insufficient Solder Amount
Nichia performed a verification test of how heat dissipation would affect the LEDs if the amount ofsolder paste is insufficient. Figure 12 shows that the smaller the amount of the solder paste is, thehigher the thermal resistance (RθJA) and TJ will be.
- Evaluated LED: Similar LEDs to the NC2W170D LED- Test Method: Nichia evaluated the RθJA and TJ values with different solder volumes by coveringcertain areas of the soldering pads with tape to apply the solder paste only to a
specified area (i.e. 25 to 100% of the whole area of the soldering pad). See Figure
11.
- PCB Used: Aluminum-core PCB with a thickness of 1.5mm, Copper layer thickness: 105μm- Input Power: 6W
Soldering Pads

Solder Paste(The solder was applied
only to the area that is
not covered with tape.)a) Soldering Pad Patternb) 25% Solder Applied to the Solderingc) 25% Solder Applied to the Soldering

Pads in Vertical Direction

Pads in Horizontal Direction

Figure 11. How the Solder Paste was Applied to the Soldering Pads for the Evaluation

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Application Note
Solder Applied in Vertical Direction
Solder Applied in Horizontal Direction

12

95

11

90
85

10
TJ (℃)

RθJA (℃/W)

Solder Applied in Vertical Direction
Solder Applied in Horizontal Direction

9
8

80
75

70

7

65

6

60

0%

20%

40%

60%

80%

100%

120%

0%

Percentage of the Soldered Area to the
Soldering Pad Area

20%

40%

60%

80%

100%

120%

Percentage of the Soldered Area to the
Soldering Pad Area

In order to ensure that the appropriate amount of solder paste is applied to the soldering pads
consistently, verify the amount of the solder paste by conducting an appearance inspection after thesolder printing and/or an X-ray examination after the LED is mounted.

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.
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/reliabilityof the LED. Nichia recommends using a nozzle specificallydesigned for the LEDs (see Figure 13). Additionally, if the tip ofthe nozzle has burrs, chipping, or foreign substances, theemitting surface may be damaged or contaminated. Ensure thatthe tip of the nozzle is cleaned before starting the pick-and-place
operations.
Vacuum pressure: ≤8N/cm2 (≤0.8kgf/cm2)
Placement pressure: ≤3.5N/mm2 max. force: 5N(Unit: mm)(2)

Light Emitting Diode

Figure 12. The RθJA and TJ Values Measured with Different Amounts of Solder Paste

R0.1(単位 Unit: mm)

Figure 13. Recommended Nozzle

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Application Note
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 14). 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

Light Emitting Diode

Correct

Correct

Incorrect

Incorrect

Incorrect

Nozzle Tip
NJSx170x

NCSx131x, NCSx170x

NC2x131x, NC2x170x

Figure 14. Nozzle Position for LED Pick-up
5.3 Nozzle Height for LED Pick-up
The recommended nozzle height for pick-up operations is where the tip of the nozzle touches the
top surface of the LED. 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.
For the LEDs in the scope of this application note, the recommended nozzle height is 0.2mm below
the edge of the embossed carrier tape pocket (see Figure 15).
This recommended nozzle height for pick-up operations has been determined by Nichia using
Nichia’s equipment and verification conditions and may not function as expected with some otherpick-and-place machines. If the pick-up operations are unstable even with using the recommended
nozzle height, adjust the nozzle height appropriate for the pick-and-place machine being used.
If the pick point of the nozzle is too high, it may cause insufficient suction power leading to picking
errors (e.g. the nozzle’s failure to pick/lift the LED into the air, incorrect picking causing the LED
to tilt when in the air) due to a large gap between the LED and the nozzle. If the pick point of thenozzle is too low, it may cause issues (e.g. causing the embossed carrier tape to shake, causing thetape pocket to deform) leading to picking failure.
NozzlePoint where the Nozzle Touches the
Top Surface of the LED (i.e. 0.2mm
below the Edge of the Pocket)
Embossed Carrier Tape

LED

Figure 15. Recommended Nozzle Height for Pick-up Operation
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Application Note
5.4 Types of Tape Feeder

Light Emitting Diode

There are two types of tape feeders: mechanical (pneumatic) feeders and electrical (motorized)
feeders. A mechanical feeder takes a pause from feeding between the LED pick-ups. This may cause
vibration resulting in the LED tilting or flipping over within the embossed carrier tape pocket. An
electrical feeder keeps feeding the tape at a constant speed without a pause; this enables stable pickup operations to be performed. Nichia recommends using a motorized tape feeder (see Figure 16).
The vibration can be reduced by slowing down the feed speed of the tape feeder. Optimize the feed
speed if suction failure occurs.

Left: Electrical
Right: MechanicalFigure 16. Tape Feeders
5.5 Top Cover Tape Removal Position and LED Pick-up Position
If the top cover tape is removed early before LED pick-up, the LED may move within the embossed
carrier tape pocket and hit the feeder cover resulting in the emitting surface being damaged. Nichia
recommends removing the top cover tape immediately before LED pick-up (see Figure 17).
Top Cover TapeNozzleFeeder Cover

Top Cover Tape Removal Position

Top Cover Tape Removal Position

Pick-up Position
Pick-up Positiona) Immediately before Pick-up (Recommended)b) Early before Pick-up

Figure 17. Top cover Tape Removal Positions

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Application Note
5.6 Measures against Static Charges
If the pick-and-place operations are performed in environments where static charges are likely tooccur (e.g. low humidity environment), the LEDs may stick to the top cover tape when the top covertape is removed due to static charges, leading to pick-up errors.
If a large amount of static charge is generated, the LEDs may
stick to the top cover tape successively as shown in Figure 18.
The following examples are recommended measures to reduce
the static charge:a) Humidity Control
Controlling humidity in the operation environment is a very effective measure against static
charges. When the humidity in the environment is greater than 50%RH, it can largely reduce static
charges that occur when removing the top cover tape (see Figure 19).
400
350

Voltage
Static帯電圧[V] (V)

Light Emitting Diode

Figure 18. LED Sticking due toStatic Charge

300
250
200
150
100
50
0
60%RH

40%RH

30%RH

20%RH

湿度管理レベル
Humidity
Control Level

Figure 19. Humidity vs. Static Voltageb) Feed Speed of the Tape Feeder
If the movement of the LEDs within the embossed carrier tape pocket is reduced by slowing down
the feed speed of the tape feeder, the static charge may be reduced (see Figure 20).
Top Cover Tape

LED

NozzleIncorrect

Correct

Embossed Carrier Tape

Feed speed is fast

Feed speed is slow

Figure 20. Feed Speed of the Tape Feeder
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Application Notec) Magnet under the Embossed Carrier Tape
If a magnet is placed under the embossed carrier tape, it may prevent the LED from sticking to
the top cover tape due to the attraction generated between the magnet and the electrodes of theLED. Use a magnet recommended for the pick-and-place machine being used (see Figure 21).

The LED and the top cover tape
are attracted by a static charge

NozzleFeeder CoverEmbossed Carrier Tape

Top Cover Tape

LED

Light Emitting Diode

Magnetic Force between the Magnet and the LED Electrodes

MagnetFigure 21. Magnet under the Embossed Carrier Taped) Changing the Top Cover Tape Removal Position
If the top cover tape removal position is changed to early before where the LED is picked up, it
may prevent the LEDs from sticking to the top cover tape. However, this may lead to the LED
hitting the feeder cover; necessary measures (e.g. using a magnet, adjusting the feed speed) should
be taken to reduce the movement of the LED within the embossed carrier tape pocket.
5.7 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 22). 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 relationship between the placement depth
and the placement speed determines the size ofthe nozzle’s placement pressure on the LED. A
Nozzlelarge placement pressure may damage theemitting surface and/or the package affecting
Placement Pressure: ≤3.5N/mm2
the performance and/or the reliability of theMaximum Force: 5N
LED. Ensure that the placement pressure isLED≤3.5N/mm2 and the maximum force applied toPlacement Depth:
the LED does not exceed 5N. The placement
0.2mm
PCB
pressure changes if there is a warpage in the
PCB; verify that the operation conditions do
Figure 22. Recommended Nozzle Heightnot cause damage to the LED in the actualfor Placement Operation
mounting process before starting the operation.
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Application Note
Examples of the Causes of the Placement Errorsa) Solder Printing Failures
If a solder printing failure (e.g. significantly small amount of the solder paste printed on the PCB)
occurs or if the LED is placed on the PCB after the solder paste is printed on it and left for a while,adhesion of the solder paste may become insufficient causing placement errors (e.g. the LED to
stick to the nozzle after placement).

Light Emitting Diodeb) Foreign Substance on the Nozzle Tip
If a foreign substance is attached to the tip of the nozzle, the LED may stick to the nozzle and not
be released after placement. Ensure that the tip of the nozzle is not contaminated and/or has no
foreign substance before pick-and-place operations.
5.8 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.
5.9 Check List for Pick-up/Placement Errors
Since the LEDs in the scope of this application note are small and lightweight, there is a possibility
that pick-up/placement errors may occur. Table 3 provides a check list to prevent the pickup/placement errors. Use the list as reference to prevent these errors.

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Application Note
Table 3. Check List to Prevent LED Pick-up/Placement Errors
Check Item

Placement
Environment
OthersLight Emitting Diode

Pick-upIs the feeder being used is an electrical(motorized) feeder?

Answer
Yes

Note

No

Mechanical feeders may cause frequent vibration; theLED may move in the tape pocket causing pick-up
errors more likely to occur.

Is the top cover tape removed
immediately before the LED pick-up
position?

Yes

No

If the top cover tape is removed early before LED pickup and that causes the emitting surface of the LED to bedamaged, change the top cover tape removal position to
immediately before pick-up. If removing the tape early
before pick-up is preferred in order to prevent static
charges, measures should be taken to reduce thevibration as much as possible (e.g. slowing down thefeed speed).

Is a magnet placed under the tapefeeder?

Yes

No

Pick-up errors caused by static charges/vibration may
be reduced by using a magnet.

Is the nozzle being used specificallydesigned for the LED according to thesize recommendations?

Yes

No

If pick-up/placement errors occur or the emitting
surface of the LED is damaged, use a nozzle
specifically designed for the LED.

Are there any contamination/foreign
substances on the tip of the nozzle?

Yes

No

Contamination/foreign substances may cause the LED
to stick to the tip of the nozzle resulting in placement
errors.

Are there any burrs, chipping, or
scratches on the tip of the nozzle?

Yes

No

Burrs/chipping/scratches on the nozzle tip may damage
the emitting surface of the LED.

Has an LED placement with a slower
placement speed been tested?

Yes

No

If the placement speed is fast, the LED may not bereleased from the nozzle (the nozzle may fail to mountthe LED).

Is the placement pressure ≤3.5N/mm2
and the maximum stress ≤5N?

Yes

No

If the placement speed is fast, the force (pressure)applied to the LED increases, which may cause theemitting surface of the LED to be damaged.

Is the pressing depth set 0.2mm?

Yes

No

If the pressing depth is too large, the force increases,
which may cause the emitting surface of the LED to bedamaged.

Is the storage temperature appropriate(not too high)?

Yes

No

If the LEDs are stored under a high temperature for along time, they may stick to the top cover tape.

Is the humidity controlled in thestorage/operation environments to
reduce static charges?

Yes

No

Controlling the humidity can reduce the occurrence of
surge from static electricity and of static charges.

Is the PCB flat (i.e. not bent/warped)?

Yes

No

If the PCB is severely warped or bent, the LED may nottouch the solder paste on the PCB properly, causing
placement errors.

Do the sizes of the metal solder stencil
apertures conform to therecommendations?

Yes

No

If the solder amount is excessively small, it may cause
placement errors.

Is the amount of solder being printed
stable?

Yes

No

If the metal solder stencil cannot release the solder
paste properly, the amount of the solder paste left on the
PCB may be extremely small, causing placement errors.

No

If the solder printing operation continues for a long
period of time or if deteriorated solder paste is used, it
may cause printing failures and/or placement errors(e.g. due to an insufficient adhesion of the solder paste).

Is the solder being used not
deteriorated?

Yes

If the answer to an item is “No”, refer to the applicable notes provided in Note column and take necessary measures.
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Application Note
6. Reflow
Preparation

SolderPrinting

Mounting

Reflow

Inspection

6.1 Reflow Conditions

Light Emitting Diode

Figure 23 shows the Nichia recommended reflow soldering conditions provided in the applicablespecification for each LED part number; use the recommended reflow conditions specified by the
manufacturer 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 the
PCB are damaged and/or the solder joint
strength is insufficient, the conditions should
be adjusted.

Figure 23. Reflow Soldering Condition (Lead-free Solder)
6.1.1 Details of the Reflow Soldering Profile
The reflow soldering profile has three zones: Pre-heat, Reflow, and Cooling. The following shows
the role of each zone.
Pre-heat zone:
The flux contained in the solder isactivated to remove the oxide film on
the PCB surface.
Reflow zone:
The heat melts the solder to form analloy.
Cooling zone:
The alloy is completed by the coolingtemperatures.
Figure 24. Example of a Reflow Profile
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Application Note
6.1.2 Adjusting the Reflow Soldering Profile

Light Emitting DiodeThe following describes how to adjust the reflow profile. Refer to Figure 25.
① Pre-heating speed (Reference: 1 to 5℃/sec)
When it is large: Solder balls are created4, possibility of voids increases5.
② Pre-heat temperature
If it is high: The solder wettability declines6.
③ Pre-heat time
If it is long: The solder wettability declines.
④ Reflow heating speed (Reference: 1 to 5℃/sec)
If it is small: The solder wettability declines6.
When it is large: Solder balls are created4, possibility of voids increases5.
⑤ Reflow peak temperature
If it is too low: The solder wettability declines, possibility of voids increases5.
If it is too high: Solder balls are created4, the solder wettability declines.
⑥ Reflow time
If it is short: possibility of voids increases5.
⑦ Cooling speed (Reference: 1.5 to 2℃/sec)
If it is large: The cause of component damage due to thermal shock.
If it is small: The cause of the decrease in solder joint strength and positional deviations.
⑧ Cooling temperature
When the temperature at the time of PCB discharge is high: Warpage occurs within the PCB.
Note:
4

If solder balls are created, it will lead to a cause of a short circuit and insulation failure.

5

An increase in voids leads to a decrease in bonding reliability and heat dissipation.

6

If the solder wettability decreases, the bonding area decreases, which leads to the decrease inbonding reliability.
Temperture

⑤

④
②

①

⑥
⑦

③

⑧
Time

Figure 25. Description of where the reflow conditions are adjusted
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Application Note
6.2 Considerations for the Transfer Board

Light Emitting Diode

When using a transfer board for machine mounting, the PCB is placed on the transfer board (transferjig) to move throughout the mounting process (see Figure 26); however, if the transfer board iswarped, mounting failures will occur. In addition, even if there is no warpage in the transfer board
in the early stages of production, warpage may occur if the same transfer board is used for the reflow
process a few dozen times. It is recommended to make sure that warping does not occur by passing
the material that would be used for the transfer board through the reflow process a few dozen times
before using it during actual production use.

Figure 26. Transfer Board

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Application Note
7. Mounting Test
After completing necessary adjustments for the mounting process, conduct inspections/tests tocheck if there are any abnormalities in the soldering conditions or the LEDs. Table 4 shows anexample of items to verify. Confirm that no issues are found in the mounting test results before
carrying out the assembly operations.
Table 4. Example of Inspection/Tests to Verify the Mounting Processes

Light Emitting Diode

Inspection

1

2

3

4

Appearance
Inspection(Visual/Imaging)

Lighting Inspection

X-Ray Examination

Shear Strength
Inspection

Check Item

Probable cause(s) when there is an abnormality/failure

Scratches
Chipping
Delamination

Inappropriate Nozzle Shape
Excessive Nozzle Placement Pressure
Burrs, Chipping, Foreign Substances on the Nozzle Tip

LED Standing on its Side

Insufficient Amount of Solder
Inappropriate Soldering Pad Pattern
Inappropriate Metal Solder Stencil Aperture Pattern
Misaligned Printing Position
Misaligned LED Placement Position
Insufficient Placement Depth for the LED Placement

Solder Balls

Excessive Amount of Solder Paste
Inappropriate Reflow Profile
Misaligned Solder Printing Position

Shape of the Solder Fillet

Inappropriate Solder Amount
Inappropriate Soldering Pad Pattern
Inappropriate Metal Solder Stencil Aperture Pattern
Inappropriate Reflow Profile

Floating
Tilt
Misalignment
Insufficient Solder
Coverage of the Soldering
Pad

Inappropriate Solder Amount
Inappropriate Soldering Pad Pattern
Inappropriate Metal Solder Stencil Aperture Pattern
Inappropriate Reflow Profile

Emission Failure

Open Circuit due to Insufficient Amount of Solder
Short Circuit due to Excessive Amount of Solder (e.g. a
Solder Bridge)
Disconnection due to Excessive Nozzle Placement
Pressure(Identify the cause using the X-ray examination)

Voids

Inappropriate Reflow Profile

Solder Balls

Excessive Amount of Solder
Inappropriate Reflow Profile

Solder Bridges

Excessive Amount of Solder

Shear Strength

Insufficient Amount of Solder
Inappropriate Soldering Pad Pattern
Inappropriate Metal Solder Stencil Aperture Pattern
Inappropriate Reflow Profile

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Application Note

Light Emitting Diode

Since the mounting status changes due to slight differences in setting conditions, as well as
differences in the solder paste, PCB, and mounting equipment/parts, etc.; always check and control
the soldering status after mounting. By using an automatic solder visual inspection system (i.e. onethat can provide an image where it is easy to judge if the image is good or if there is a defect), it ispossible to improve the efficiency of work and reduce the dependence on the operator’s skill
compared to visual inspection (see Figure 27).

Figure 27. Example of the Inspection Using an Automatic Solder Visual Inspection System

8. Inspection
Preparation

SolderPrinting

Mounting
FailureReflow

Inspection

8.1 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.
8.1.1 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 connection7 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 current8 may temporarily flow through the LEDs due to the inrush current(see Figure 28) causing damage to the LEDs (see Figure 29).
a hot-wire connection4

absolute maximum rating current5

Note:
74

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

85

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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Application Note
Current
Peak Current
Inrush Current
Constant Current
Time

Figure 28. Example of an inrush current waveform

Damaged Electrodes of the LED
chip due to an Inrush Current.

Figure 29. Example of an LED Damaged
due to an Inrush Current

Light Emitting Diode

8.2 Electrical Characteristics Inspection
An electrical characteristics inspection should be performed to confirm that the designed value ofthe current flows through the LED when it is operated and that the voltage value is appropriate forthe current flowing through the LED.
8.3 Appearance Inspection
An 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.).
8.4 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.

9. 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 be
applied to the LEDs.

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Application Note
10. Summary

Light Emitting DiodeThe 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. In cases where the mounting operations are not successful with
Nichia’s recommended conditions, it is best for customers to understand the trends for the processes
chosen for the applications, accumulate actual test data, and be able to respond daily to any necessarychanges/adjustments to the processes.

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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.

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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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