Application Note

Light Emitting DiodeHow to Hand Solder anElectric Wire to a COB LED

Table of contents
1. Overview ........................................................................................................ 2
2. Necessary/Recommended Soldering Equipment ........................... 3
3. How to Choose the Optimal Soldering Iron Tip .............................. 4
4. Cautions/Suggestions for Stripping the Wire................................... 5
5. Procedure for Soldering an Electric Wire to a COB LED ............... 6
6. Potential Issues after Soldering Electric Wires to COB LEDs ....... 6
7. Cautions/Suggestions for Replacing Soldering Iron Tips ............ 8
8. Summary ........................................................................................................ 8This document contains tentative information, Nichia may change the contents without notice.
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Application Note
1. Overview

Light Emitting Diode

It is more difficult to solder an electric wire to a COB LED by hand than to solder a typical
discrete LED to a PCB by hand; there are potential issues to consider when establishing
an electrical connection between the COB LED and the housing/heat sink with an electric
wire:- COB LEDs have substrates with good heat dissipation; this can cause the substrate toabsorb the heat of the soldering iron, preventing the solder from melting properly
and leading to reduced workability.
- When soldering an electric wire to a COB LED, the process may reduce the dielectricstrength of the COB LED depending on how it will be operated.
- During and/or after soldering an electric wire to the electrode, if tension is applied tothe electric wire, it may cause the electrode to delaminate causing a catastrophic
failure (i.e. the COB LED not to illuminate)This application note provides information on how to solder an electric wire to a COB LED
and cautions/suggestions for this process, considering the issues above.
Note:
Nichia recommends using specially designed holders to attach COB LEDs to thehousings/heat sinks for the electrical connection to reduce the potential for reliability
issues.

GoodGoodHeatDissipation

Workability

BadBadThis document contains tentative information, Nichia may change the contents without notice.
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Application Note
2. Necessary/Recommended Soldering Equipment
For successful soldering, it is important to use a soldering iron that ensures that thecontact area between the iron and the metal to be joined (i.e. the COB LED’s electrode) is
maximized to conduct the heat efficiently. Ensure that the chosen soldering iron isappropriate for the electrodes of the LED. For general information on necessary
equipment (i.e. soldering station) including soldering irons, refer to Figure 1 below.

Temperature Controller

Soldering Iron Stand

Light Emitting Diode

Recommended Hand
Soldering Condition

If the tip of the soldering
iron becomesoxidized/blackened andwill not come clean after
wiping on a damp
cleaning sponge, thecleaning wire can be usedto remove the oxidationfrom the soldering tip.

Temperature 380°C Max
SolderingTime

Cleaning Wire

5sec Max

Cleaning Sponge

Soldering Iron

If the soldering iron is turned on and left for a while,
it will cause the tip to become very hot causingoxidation to occur on the working surface of the tip;
this will cause the tip to discolor (i.e. blacken). If thisoccurs, the solder will not wet (i.e. melt) on the tip
surface; the oxidized tip should be cleaned on thedamp sponge.

Ensure that the shape of the soldering iron
tip is selected accordingly for its intended
purpose. To solder electric wires to COB
LEDs, tips with high heat capacities should
be used. For more details on the types oftips that might be useful for this purpose,refer to Table 1.

Figure 1. Example of a Soldering Iron (Manufactured by HAKKO)

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Application Note
3. How to Choose the Optimal Soldering Iron Tip
Ensure that a tip size/shape is selected that is optimal for soldering the electric wire tothe COB LED. In terms of ease of use, the optimal tip shape/size may vary depending on
the operation; in terms of workability, as the area of contact between the tip and themetal to be joined (e.g. COB LED's electrode) increases the workability improves. For
more information (e.g. types of tip shapes, cautions/suggestions for selecting sizes),refer to Table 1 below.

Table 1. Uses for Different Types of Soldering Iron Tips

Light Emitting DiodeTip ShapeType B

Tip Characteristics

Cautions/Suggestions

Conical tips are capable of being used

Slightly thick and rounded tips

from any direction with easy handling.

are recommended when

While the pointed tip helps conduct

soldering electric wires to COB

heat to small areas more efficiently, it

LEDs as they are easy to use.

also can be used for large areas.

Type BC

Slightly thick and rounded tips are

Ensure that when soldering an

recommended when soldering electric

electric wire to a COB LED withwires to COB LEDs as they are easy tothis type of tip, the size of theuse.

beveled edge is appropriate forthe electrode size of the COBLED.

Conical tips with beveled edges. The
size of the beveled edges can beType C

chosen that best fits the size of the-metal to be joined.
Flat screwdriver type tip. Depending on
how the flat pointed tip is applied it
Type Dcan be used three ways: as a point, a-line, or to an area.
Tips with edges that resemble a knife.
This type of tip also can be used forType K

points, lines, or areas. It is also useful-for narrow pitches or to fix soldering
errors (e.g. removing solder bridges).

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Application Note
4. Cautions/Suggestions for Stripping the Wire
When soldering an electric wire to a COB LED ensure that it provides a necessary creepage
distance and does not reduce the dielectric strength of the COB LED. Refer to Figure 2
below for more details on how to remove the insulating material from the wire.

Electrode(Metal to be joined)
Place the electric wire in a manner that:

Light Emitting Diode1. leaves a space between the starting end of theexposed wire and the edge of the electrode.
Exposed Electric
Wire (Gray)

Electrode(Yellow)

Insulated Electric
Wire (Red)

2. leaves no space between the endof the exposed wire and the edgeof the electrode.

Caution: To prevent a shortage of creepage
distance and the resulting reduction in thedielectric strength, ensure that the exposedinternal wire does not extend beyond thearea indicated by the red-dotted line.

Figure 2. Schematic diagram of how to strip the wireThis document contains tentative information, Nichia may change the contents without notice.
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Application Note
5. Procedure for Soldering an Electric Wire to a COB LED
Refer to Table 2 below for the details of how to solder an electric wire to the electrode ofa COB LED. Ensure that when performing the soldering operations (i.e. Step 2: Pre-plating
and Step 4: Soldering the Electrical Connection), the total operation time of thesesoldering operations combined is no longer than 5 seconds.
Note that this is an example provided for reference purposes only.
Table 2. How to Solder an Electric Wire to the COB LED’s Electrode (Example)

Light Emitting Diode

1. Stripping the Wire

2. Pre-plating

3. Attaching the COB

4. Soldering theLED to the heat sink

Electrical Connection

Adjust the length of

Apply appropriate

Before soldering:

Heat the electrodethe exposed internal

amounts of solder toattach the COB LED towith a soldering iron towire to suit the size ofboth the electrodethe heat sink, thenmelt the pre-plating

the electrode.

surface and thedecide the positions ofsolder. When theexposed portion of thethe electric wires onsolder begins to melt,

electric wire (i.e. pre-the electrodes andattach the electricalplating).

clamp the electric wires

wire to the electrode.

to the heatsink awayfrom the electrodes.

Note: Ensure that the electric wires are clamped on the heat sink away from the electrodes
before soldering them to the electrodes. Otherwise, it may cause damage to theelectrode (e.g. electrode delamination) when the electric wire is pulled.

6. Potential Issues after Soldering Electric Wires to COB LEDs
Electrode delamination is a commonly reported issue for cases where electric wires areused with COB LEDs for the electrical connection. This issue can occur when excessive
force is applied to the electric wire after soldering it to the COB LED.

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Application Note

Delaminated Electrode

Delaminated ElectrodeDuring and/or after soldering an electric wire to the electrode, ensurethat tension is not applied to the electric wire. This may cause theelectrode to be damaged and/or reduce the adhesive strength of theelectrode to the package. In order to prevent tension from occurringon the lead, using a mechanism to clamp the lead (e.g. cable/cord clips,clamps, etc.) on the housing side is recommended.
As mentioned earlier in this section, electrode delamination may occur when excessive
tension is applied to the electric wire. In addition, solder paste components (e.g. halogens)may cause the adhesive strength between the COB LED’s electrode and substrate todecrease, leading to electrode delamination. Ensure that sufficient verification isperformed to determine the effect of the chosen solder paste on the adhesive strength.
Refer to Figure 4 below for empirical data showing how the difference in solder paste
affects the adhesive strength over time.
120

Relative Adhesive Strength [%]Light Emitting DiodeFigure 3. Electrode Delamination (Example of a Reported Failure)

1008060

Solder A

40

Solder B

Storage Conditions:

2085°C /85%RH

00100200300

400

500

600

700

8009001000

1100

Test Duration [hr.]Figure 4. Reduction in the Adhesive Strength between the Electrode and Substrate over
Time (Example)

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Application Note
7. Cautions/Suggestions for Replacing Soldering Iron Tips
Lead-free solders are higher in tin content than lead solders; tin can erode the tip plating
causing the tip to wear out. This will affect the workability significantly. Ensure that if a
lead-free solder is used, regular checks are made to determine when to replace the tips.

Light Emitting Diode

8. Summary
This application note has provided information on:- Example of how to solder an electric wire to a COB LED by hand
- Potential issues associated with this connection method (e.g. electrode delamination
due to excessive tension applied to the electric wire and the type of solder used)- Alternative solution on how to secure/connect a COB LED (i.e. specially-designed COBLED holder)The optimal soldering equipment/conditions for attaching an electric wire to a COB LED
may vary depending on a range of factors. Those that better fit the chosen application
should be determined by performing multiple runs using different conditions.
Additionally, ensure that sufficient verification is performed with the type of solder being
used to ensure that there are no issues (e.g. electrode delamination).

This document contains tentative information, Nichia may change the contents without notice.
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Application Note

Light Emitting DiodeDisclaimer
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 license under or immunity from any intellectual property rights or other rights heldby Nichia or third parties.
 Nichia makes no representation or warranty, express or implied, as to the accuracy,completeness or usefulness of any information contained herein. In addition, Nichia
shall not be liable for any damages or losses arising out of exploiting, using, ordownloading or otherwise this document, or any other acts associated with thisdocument.
 The content of this application note may be changed without any prior or subsequent
notice.
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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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