AUTOMOTIVE

LUXEON FX2
Assembly and Handling Information

Introduction
This application brief addresses the recommended assembly and handling
procedures for LUXEON FX2. The LUXEON FX2 is designed to deliver high luminous
flux and efficacy in automotive exterior lighting applications. As a matter of principle,
LEDs require special assembly and handling precautions.

Proper assembly, handling and thermal management, as outlined in this application

brief, ensures high optical output, long term lumen maintenance and high reliability
of the LUXEON FX2 in automotive applications.

Scope
The assembly and handling guidelines in this application brief apply to the products:

PRODUCTS

LUXEON FX2 Cool White

LUXEON FX2-L Cool White
LUXEON FX2 Plus Cool White
LUXEON FX2-L Plus Cool White
LUXEON FX2 PC Amber
LUXEON FX2-L PC Amber
LUXEON FX2 Plus PC Amber
LUXEON FX2-L Plus PC Amber

Any assembly or handling requirements that are specific to a subset of the

LUXEON FX2 products is clearly marked.

In the remainder of this document, the term LUXEON FX2 refers to any product in
the LUXEON FX2 product family.

Where further differentiation between the two package size are necessary the term
LUXEON FX2 Plus refers to all family members carrying a Plus in their description.

AB183 LUXEON FX2 Application Brief ©2023 Lumileds Holding B.V. All rights reserved.
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1. Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.1 Reference Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 Form Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.4 Optical Center . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.5 Mechanical Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2. Handling Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1 Electrostatic Discharge (ESD) Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.2 Component Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3 Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3. Printed Circuit Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.1 PCB Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2 Footprint and Land Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.3 Surface Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.4 Solder Mask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.5 Silk Screen or Ink Printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.6 PCB Quality and Supplier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4. Thermal Measurement Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.1 Thermal Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.3 Thermal Measurement Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5. Assembly Process Recommendations and Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5.1 Solder Paste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5.2 Stencil Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5.3 Pick and Place Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

5.4 Placement Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.5 Feed System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.6 Reflow Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

5.7 Reflow Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 2
 5.8 Board Handling and Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

5.9 Packing of Assembled LUXEON FX2 Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

6. Interconnect Reliability Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7. JEDEC Moisture Sensitivity Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

8. Product Packaging Consideration – Chemical Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 3
1. Component
1.1 Reference Document
The LUXEON FX2 datasheets are available upon request. Please contact your sales representative.

1.2 Description
The LUXEON FX2-LED consists of a single chip, combined with a phosphor converter. This LED Chip is placed on an AIN
carrier substrate and the electrical and thermal pads are formed on the bottom side of this AlN carrier. The outside of the
package is coated with white silicone to shield the chip from environment and to prevent light leakage to the sides (top
emitter). The LUXEON FX2-LED includes a separate transient voltage suppressor (TVS) chip on top of the carrier substrate,
that is covered by side coat. The TVS shall protect the emitter against electrostatic discharges (ESD). For the subset
LUXEON FX2 Plus a dedicated thermal pad is located beneath the LED chip as can be seen in Figure 2.

Figure 1. Top view (left) and bottom view (right) of the LUXEON FX2

Figure 2. Top view (left) and bottom view (right) of the LUXEON FX2 Plus

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 4
 Table 1. Design features by LUXEON FX2 part number

NOMINAL
LIGHT EMITTING
PRODUCT PRODUCT DRIVE PACKAGE SIZE NUMBER ESD
PART NUMBER AREA
PHOTO DESCRIPTION CURRENT (mm) OF PADS PROTECTION
(mm)
(mA)

A1F2-5850S2Axxxxx 1000 1.50 x 1.85 x 0.798

Internal
FX2 CW 1.06 x 1.06 2
TVS-diode
A1F2-5850S2Cxxxxx 1000 1.50 x 1.85 x 0.813

A1F2-5850F2Axxxxx 1000 1.50 x 1.85 x 0.798

Internal
FX2-L CW 1.15 x 1.15 2
TVS-diode
A1F2-5850F2Cxxxxx 1000 1.50 x 1.85 x 0.813

Internal
FX2 PCA A1F2-0591S2Axxxxx 1000 1.50 x 1.85 x 0.838 1.06 x 1.06 2
TVS-diode

A1F2-0591F2Axxxxx 1000 1.50 x 1.85 x 0.838

Internal
FX2-L PCA 1.15 x 1.15 2
TVS-diode
A1F2-0591F2Cxxxxx 1000 1.50 x 1.85 x 0.890

Table 2. Design features by LUXEON FX2 Plus part number

NOMINAL LIGHT
NUMBER
PRODUCT PRODUCT DRIVE PACKAGE SIZE EMITTING ESD
PART NUMBER OF
PHOTO DESCRIPTION CURRENT (mm) AREA PROTECTION
PADS
(mA) (mm)

A1F2-5850S3Axxxxxx 1000 1.92 x 2.34 x 0.798

Internal
FX2 Plus CW 1.06 x 1.06 3
TVS-diode
A1F2-5850S3Cxxxxx 1000 1.92 x 2.34 x 0.813

A1F2-5850F3Axxxxx 1000 1.92 x 2.34 x 0.798

A1F2-5850F3Bxxxxxx 1000 1.92 x 2.34 x 0.807 Internal

FX2-L Plus CW 1.15 x 1.15 3
TVS-diode

A1F2-5850F3Cxxxxx 1000 1.92 x 2.34 x 0.813

Internal
FX2 Plus PCA A1F2-0591S3Axxxxx 1000 1.92 x 2.34 x 0.838 1.06 x 1.06 3
TVS-diode

A1F2-0591F3Axxxxx 1000 1.92 x 2.34 x 0.838

FX2-L Plus Internal
1.15 x 1.15 3
PCA TVS-diode
A1F2-0591F3Cxxxxx 1000 1.92 x 2,34 x 0.890

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 5
 1.3 Form Factor
The dimensional design for LUXEON FX2 is outlined below in Figure 3 and for LUXEON FX2 Plus in Figure 4. The different
dimensions, related to the type, are listed in Table 1 and Table 2. See the latest LUXEON FX2 datasheet for detailed
dimensions and applicable tolerances.

Top View Side View Bottom View

Figure 3. Outline dimensions for LUXEON FX2

Top View Side View Bottom View

Figure 4. Outline dimensions for LUXEON FX2 Plus

1.4 Optical Center

The LUXEON FX2 has no lens (primary optics). The optical center is at the center of the ceramic phosphor converter as
indicated by the red dot, and the center of LED package is indicated by the green dot, both shown in Figure 5. The distance
of optical center to package center is nominal 0.46mm. See datasheet for latest information on tolerances. Optical rayset
data of each LUXEON FX2 part is available upon request.

Optical
Center

0.18 mm

Package
Center

Top Bottom
Figure 5. Nominal optical center and geometrical package center for LUXEON FX2

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 6
 Optical
Center

0.46 mm

Package
Center

Top Bottom
Figure 6. Nominal optical center and geometrical package center for LUXEON FX2 Plus

1.5 Mechanical Files

Mechanical drawings and CAD-files for the LUXEON FX2 are available upon request. For details, please contact your sales
representative.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 7
2. Handling Precautions
2.1 Electrostatic Discharge (ESD) Protection
As shown in Table 1 and 2, the LUXEON FX2 is ESD protected by an additional TVS device. This transient voltage suppressor
(TVS) diode provides a current path for transient voltages (see Figure 7).

Figure 7. Electrical schematic of an LED with internal TVS

Common causes of ESD inlude the direct transfer of charges from the human body or from a charged conductive object to
the LED component. In order to test the susceptibility of LEDs to these common causes of ESDs, two different models are
typically used:

• Human Body Model (HBM)

• Charged Device Modell (CDM)

The LUXEON FX2 has been independently verified to successfully pass ESD tests under HBM and CDM conditions. For
the respective test voltages of these tests please refer to the latest LED datasheets. Additional external ESD protection
for the LED may be needed if the LED is used in non ESD-protected environments or exposed to higher ESD voltages and
discharge energies, e.g. as described in ISO 10605 or IEC 61000-4-2 (severity level IV). For details please contact your sales
representative.

Machine (MM) is redundant to HBM at the device level since it produces the same failure mechanisms and the two models
generally track each other in robustness and in failure modes produced and is therefore obsolet.

2.2 Component Handling

Minimize all mechanical forces exerted onto the LED package. It should not be handled with tweezers that can lead to
damage of the package, especially not with metallic tweezers. Any force above 2.0 N may damage the LED and change
optical performance. A vacuum pen can be used instead of tweezers (see Figure 8)

The suction tip should be made of a soft material such as rubber to minimize the mechanical force exerted onto the top
surface of the LED. Avoid contaminating the top side surface of the LED. Do not stick any tape on top of the light emitting
surface, such as Kapton™- or UV-tape. A contamination with glue or its invisible constituent parts may change the LED
performance.

Electrical testing before assembly should be avoided. Probe tips may scratch or dent the pad surface, which may lead to
solder issues, and damage the LED. Avoid any contact with the LED other than what is required for placement.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 8
 VAC.

Figure 8. LED handling

Do not touch the top surface with fingers or apply any pressure to it when handling finished boards equipped with LEDs.
Do not stack finished boards because the LEDs can be damaged by the other board outlines. In addition, do not put
finished boards with LEDs top side down on any surface. The surface of a workstation may be rough or contaminated and
may damage the LEDs. These warnings are shown in Figure 9.

Figure 9. Board handling

2.3 Cleaning
The surface of the LED should not be exposed to dust and debris. Excessive dust and debris on the LED surface may cause
a decrease in light output and optical behavior. It is best to keep LEDs in their original shipping reel until actual use.

In the event that the surface requires cleaning, a compressed gas duster or an air gun with 1.4 bar (at the nozzle tip) and a
distance of 15 cm will be sufficient to remove the dust and debris. Make sure that the parts are secured first, taking above
handling precautions into account.

One can also rinse with isopropyl alcohol (IPA). Do not use solvents listed in Table 12, as they may adversely react with
the LED assembly. Extra care should be taken not to damage the housing around the LED chips. Lumileds does not
recommend ultrasonic supported cleaning for LEDs.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 9
3. Printed Circuit Board
3.1 PCB Requirements
The LED can be mounted on multi-layer FR4 printed circuit boards (PCB) or insulated metal substrates (IMS). To ensure
optimal operation of the LED, the thermal path between the LED package and the heat sink should be optimized according
to the application requirements. Please ensure that the PCB assembly complies to the applicable IPC standards listed
below.

General PCB Standards:

• IPC A-600H: Acceptability of Printed Boards

• IPC A-610F: Acceptability of Electronic Assemblies
• IPC 2221A: General Standard on Printed Board Design
• IPC 7093: Design and Assembly Process Implementation for Bottom Termination Components

Filled and capped via boards:

• IPC 4761: Design Guide for Protection of Printed Board Via Structures
• IPC 2315: Design Guide for High Density Interconnects and Micro Vias
• IPC 2226: Design Standard for High Density Interconnect Printed Boards

3.2 Footprint and Land Pattern

Lumileds recommends for the LUXEON FX2 using of a metal defined land pattern, as shown in Figure 10. Consider that
metal defined land pattern, leaves less area for the heat spreading of the thermal power, generated by the LED. Also
higher tolerances for LED tilting and position tolerances can be encountered. Positive aspect is, that the requirements to
the printed circuit board tolerance for solder mask alignment to metal structure are lower than for solder mask defined
land pattern.

Figure 10. Metal defined land pattern for LUXEON FX2

For the LUXEON FX2 Plus, Lumileds recommends a solder mask defined land pattern, as shown in Figure 11. The copper
area can be extended as far as possible for better heat spreading, which results in lower thermal resistance. However,
a solder mask defined pad requires good mask quality and tight registration tolerances during PCB manufacturing (see
Chapter 3.7 “PCB Quality and Supplier” for more details).

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 10
 For the solder mask defined land pattern, the self-alignment of the component during reflow soldering can be controlled
well by solder mask geometry in X- and Y-direction.

Figure 11. Metal defined land pattern for LUXEON FX2 Plus

3.3 Surface Finishing

Lumileds recommends using ENIG (Electroless Nickel Immersion Gold) plating according to IPC-4552. Other surface
finishes are possible but have not been tested by Lumileds. Surface finish Hot-Air-Solder-Leveling (HASL) may have
inhomogenious pad height and is not recommended. Unsymmetrical solder thickness may have an influence on LED
height and soldering tolerances. The actual quality of HASL finish shall be checked in each single case.

3.4 Solder Mask

A flat solder mask thickness on top of metal layer is desired. Solder mask thickness variation and offset tolerances have
impact on solder quality and post-solder position accuracy. Mask and PCB vendors have to be evaluated for proper quality.
Detailed specifications and information regarding solder mask requirements are contained in IPC-6012 and IPC-SM-840.
(see chapter “PCB Quality and Supplier”, Figure 12 for more details).

3.5 Silk Screen or Ink Printing

Silk screen markings within and around the LED outline should be avoided because the height of the ink may interfere with
the solder stencil printing process.

3.6 PCB Quality and Supplier

Select only PCB suppliers that are capable of delivering the required level of quality. The PCBs must comply with IPC
standard IPC-A-600J, 2016 (“Acceptability of Printed Boards”) or superseding3I document.

A maximum mask registration tolerance of 50 µm between the copper trace pattern and solder mask is desirable to
achieve optimum solder joint contact area using the recommended solder mask defined footprint as shown in Figure 10.
If the offset between the solder mask and the copper land pattern is large, one side of electrode pads will have less solder
joint contact area. This may affect package centering, tilting, and thermal performance and may increase risk of solder
bridging (short circuit) and solder balling if the stencil is not properly aligned to the solder mask during printing.

Figure 12 shows an example of the solder pad size for different registration offset levels between the copper trace pattern
and the solder mask for LUXEON FX2 using the recommended footprint in Figure 12. Large misalignment between solder
mask opening and copper trace will cause one of the two electrode copper land patterns to be smaller than the other.
Depending on the PCB manufacturer capability, PCB cost consideration and customer position tolerance needs, it may be
necessary to extend the area of the solder mask opening.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 11
 Figure 12. Solder mask registration offset to copper trace

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 12
4. Thermal Measurement Guidelines
4.1 Thermal Resistance
The thermal resistance between the junction of the LED and the bottom side of the PCB depends on the following key
design parameters of a PCB:

• PCB dielectic materials

• Cu plating thickness
• Solder pad pattern and solder thickness
• Distance to neighbogring heat source (LED spacing)

Lumileds conducted simulations to evaluate the thermal performance of LUXEON FX2 on different PCB design concepts.
Details of the simulation model are given in Figure 13. The model geometry comprises the LED on a board (metal-core
printed circuit board or FR4 board) that is mounted on a plate Al heatsink. A thermal interface material (TIM) is assumed
between board and heatsink. The thermal resistances junction-to-board bottom Rth,j-b,el (thermal resistance based on
electrical input power) are calculated as Rth,j-b,el = Rth,j-b,real/(1–WPE), where WPE denotes the wall plug efficiency. The WPE is
not constant and depends on drive condition and flux binning class. The thermal resistance Rth,j-b,real is based on thermal
power and is obtained by Rth,j-b,real = (Tj-Tb)/Pth, where Tj is the average junction temperature, Tb the maximum temperature at
the bottom side of the board obtained from the simulations, and Pth the thermal input power.

Simulation Details

Simulation
• Model Board Thermal Conductivities

• LED on board and plate heat sink with TIM • Cu: 390 W/(mK)
• Simulation of heat conduction and radiation • IMS dielectric: 2.2 W/(mK) or 3 W/(mK)
• Bottom of heat sink is assumed to be ideally • FR4 epoxy: 0.3 W/(mK)
heat-sunk to ambient
• Vias plating: 390 W/(mK)
Heat Sink and TIM Parameters • Vias filling: 0.3 W/(mK)
• Heat sink size: 50 mm x 50 mm x 5 mm • Solder mask: 0.2 W/(mK)
• Heat sink material: Al – 150 W/(mK) Solder Parameters
• TIM thickness: 100 µm
• Thickness (BLT): 90 µm
• TIM th. cond.: 2 W/(mK)
• Th. conductivity: 56 W/(mK)
Board Parameters

• Board area: 20 mm x 20 mm
• Board thickness: 1.0 mm (Cu-IMS) or 1.6 mm
(Al-IMS, FR4)
• Cu layer thickness: 70 µm
• Solder mask: 20 µm
• IMS diel. thickness: 75 µm or 38 µm

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 13
 Figure 13. Model geometry and board parameters used for the simulation

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 14
 Table 3a and 3b list the simulated LED-junction-to-board-bottom thermal resistances Rth,j-b,real (based on thermal power)
and the thermal resistances Rth,j-b,el (based on electrical power) for LUXEON FX2 Plus and LUXEON FX2 on different
board. The thermal resistances Rth,j-b,el have been calculated assuming a WPE for LUXEON FX2 CW and LUXEON Plus CW
of 0.3, as well for LUXEON FX2 PCA and LUXEON FX2 Plus PCA of 0.25.

Table 3a. Simulated thermal resitances for LUXEON FX2 Plus

LUXEON FX2 PLUS CW LUXEON FX2 PLUS PCA
BOARD MATERIAL/DIELECTRIC Rth,j-b,el Rth,j-b,real Rth,j-b,el
Rth,j-b,real
(K/W) (K/W) (K/W) (K/W)
1.0 mm Cu-IMS, 3 W/(mK) – 38 µm dielectric 7.6 5.3 7.6 5.7
1.0 mm Cu-IMS, 2.2 W/(mK) – 75 µm dielectric 9.0 6.3 9.0 6.7
1.6 mm Al-IMS, 3 W/(mK) – 38 µm dielectric 7.8 5.5 7.8 5.9
1.6 mm Al-IMS, 2.2 W/(mK) – 75 µm dielectric 9.2 6.5 9.2 6.9
1.6 mm FR4 with filled and capped vias in thermal
12.0 8.4 12.0 9.0
pad region
1.6 mm FR4 with open vias around thermal
14.6 10.2 14.6 10.9
pad, no bottom solder mask
1.6 mm FR4 with open vias around thermal
16.2 11.3 16.2 12.2
and electrical pads, bottom solder mask

Table 3b. Simulated thermal resitances for LUXEON FX2

LUXEON FX2 CW LUXEON FX2 PCA
BOARD MATERIAL/DIELECTRIC Rth,j-b,el Rth,j-b,real Rth,j-b,el
Rth,j-b,real
(K/W) (K/W) (K/W) (K/W)

Cu-IMS 1.0 mm 3 W/(mK) 38 µm dielectric 8.4 5.8 8.4 6.3

Cu-IMS 1.0 mm 2.2 W/(mK) 75 µm dielectric 9.8 6.8 9.8 7.3

Al-IMS 1.6 mm 3 W/(mK) 38 µm dielectric 8.6 6.0 8.6 6.5

Al-IMS 1.6 mm 2.2 W/(mK) 75 µm dielectric 10.0 7.0 10.0 7.5

FR4 F&C vias 1.6 mm 12.8 8.9 12.8 9.6

FR4 open vias 1.6 mm, no bottom SM 15.4 10.7 15.4 11.5

FR4 open vias 1.6 mm 17.0 11.8 17.0 12.8

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 15
 4.2 Close-Proximity Thermal Performance
The For small distances between the individual LEDs, thermal crosstalk can occur, leading to enhanced junction
temperatures. Lumileds recommends using thermally well performing boards with high-conductivity dielectric to optimize
the thermal performance.

Lumileds conducted thermal simulations of a 2x2 and a 2x3 LED arrangement of varying distance between the LEDs as
schematically shown in Figure 14. The thermal resistances Rth,j-b,real of an Al-IMS board and an FR4 board with filled and
capped vias in the thermal pad region were analyzed. The board size was 60 mm x 60 mm. The vias region in the FR4
epoxy was modelled as a region of anisotropic thermal conductivity with an in-plane conductivity of k|| = 0.3 W/(mK) and
an out-of-plane conductivity of k^ = 38 W/(mK), corresponding to a fractional Cu area of ~10%. This value is in line with
the vias pattern given in Figure 13. Other board parameters are chosen as described in section 4.1 The same power was
assigned to all LEDs in the array. The simulated thermal resistances from junction to board bottom Rth,j-b,real are given in the
graphs in Figure 14. They have been calculated using the simulated junction temperature and the thermal power of an
individual LED according to:

Rth,j-b,real = (Tj(1 LED) – Tb,max)/Pth(1 LED).

Figure 14. (a) Simulated thermal resistance Rth,j-b,real as a function of the gap d between the LEDs for a 2x2 array configuration,
(b) simulated thermal resistance Rth,j-b,real as a function of the gap d between the LEDs for a 2x3 array configuration.
The thermal resistance values in (a) and (b) refer the power of one LED.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 16
 4.3 Thermal Measurement Instructions
The use of a temperature probe may be desirable to verify the overall system design model and expected thermal
performance. Different methods exist to determine the LED temperature in terms of case temperature Tc, junction
temperature Tj, or phosphor temperature Tph.

Table 4 lists three methods along with the expected measurement accuracy. The more accurate a measurement is, the
closer Tc and Tj can be designed to their maximum allowable values as specified in the LUXEON FX2 datasheets.

Table 4. Temperature measurement methods

METHOD ACCURACY (°C) EFFORT EQUIPMENT COST

Thermo sensor (e.g. thin wire thermocouple) ±2.0 to ±5.0 [1] Low Low
Forward voltage measurement ±0.5 High High
Infrared thermal imaging ±2.0 to ±10.0 [2] Medium High
Notes for Table 4:
1. See “Temperature Probing by Thermo Sensor” for parameters determining the measurement accuracy.
2. See “Temperature Measurement by Infrared Thermal Imaging” for parameters determining the measurement accuracy.

Figure 15. Temperature probing by thermo sensor

Figure 15 schematically shows the LED soldered to a PCB, including the relevant temperatures as defined for specific
positions in the setup. Since the LED is directly soldered to the board, the case temperature is equal to the temperature
of the solder material Tsolder. A practical way to verify the case temperature Tc is to measure the temperature Tsensor on a
predefined sensor pad thermally close to the case by means of a thermocouple or a thermistor as shown in Figure 15.

The case temperature can be calculated according to the following equations:

Tc = Tsensor + Rth,c-sensor,el • Pel

Tc = Tsensor + Rth,c-sensor,real • Pth

In these equations, Tsensor is the sensor temperature at the predefined location, Pel the electrical power of the LUXEON FX2
emitter, Pth = Pel • (1 – WPE) the thermal power of the LUXEON FX2 emitter, Rth,c-sensor,el the thermal resistance between
case and sensor point based on the electrical power, and Rth,c-sensor,real the thermal resistance between case and sensor
point based on the thermal power. The thermal resistances Rth,c-sensor,real and Rth,c-sensor,el are application specific and can be
determined with help of thermal simulations and measurements. Lumileds has determined the typical Rth,c-sensor,real and
Rth,c-sensor,el for LUXEON FX2 on different board types (see Table 5). Please refer to section 4.1 for more detailed information
regarding the board design parameters. The sensor has been mounted at a distance of 0.5mm to the edge of the package
as indicated in Figure 15. The accuracy of the measurement depends on the board type, the measurement accuracy of
the thermocouple, and the mounting position. The temperature signal at the thermo sensor measurement point is higher
for boards with large heat spreading in the top Cu layer (typically boards with low-conductive dielectric). LED boards with
different configuration, design, or material from the ones given in Table 5 may require additional thermal modeling or
measurements to determine the right case-to-sensor thermal resistances.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 17
 Table 5. Typical Rth,c-sensor,real and Rth,c-sensor,el values of different board concepts

LUXEON FX2 PLUS COOL WHITE LUXEON FX2 PLUS PC AMBER

BOARD TYPE Rth,c-sensor,real Rth,c-sensor,el Rth,c-sensor,real Rth,c-sensor,el

(K/W) (K/W) (K/W) (K/W)

Double-layer FR4 board with filled and capped vias 8.0 5.6 8.0 6.0
IMS with dielectric of 3 W/(mK), 38 µm thickness 5.0 3.5 5.0 3.7
IMS with dielectric of 2.2 W/(mK), 75 µm thickness 6.0 4.2 6.0 4.5

Temperature Probing by Forward Voltage Measurement

The forward voltage measurement uses the temperature dependence of the LED’s forward voltage Vf. The forward voltage
after switching off the thermally stabilized system is measured and analyzed, yielding information on the LED junction
temperature. By using a thermal model of LUXEON FX2 or the LED junction-to-case thermal resistance as indicated in the
datasheet, the case temperature Tc can be estimated. To ensure high accuracy, a precise and fast voltage measurement
system is needed. In addition, the relationship between forward voltage and temperature needs to be properly
characterized for each individual LED. Please contact your sales representatives for further support in this topic.

Temperature Probing by Infrared Thermal Imaging

Infrared (IR) thermal imaging can be used to measure the surface temperature/phosphor temperature of the LED or
the board temperature. Lumileds does not recommend using IR measurements to estimate the LED junction or case
temperature.

For an accurate determination of the absolute temperature via IR thermography, the determination of the exact emissivity
value is crucial. The emissivity generally depends on material, surface properties, and temperature. It can be determined
by heating up the unbiased device to a defined temperature that can be, for example, measured with a thermocouple.
Then, an IR measurement can be taken of this setup, and the emissivity setting of the material of interest (typcially the
phosphor or the board surface) can be adjusted to match the thermocouple reading. The obtained emissivity value can
be used to evaluate the IR image of the device in operation to determine the temperature of interest. The temperature at
which the emissivity value is determined should be similar to the temperature in operation that is to be measured. During
IR imaging, make sure that the recorded image is not disturbed by unwanted background reflections. Due to the small
dimensions of the LUXEON FX2, an imaging system with high magnification should be used in order to get a sufficient
resolution of the LED in the IR image.

Note that due to losses in the phosphor converter layer, the phosphor temperature of the LUXEON FX2 is typically higher
than the LED junction temperature. The absolute temperature difference depends on the drive current and on the type of
phosphor.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 18
5. Assembly Process Recommendations and Parameters
5.1 Solder Paste
For reflow soldering, a standard lead free SAC solder paste (SnAgCu) with no clean flux can be used. The majority of the
Lumileds internal testing has been conducted with the Innolot solder paste, which showed reasonable reflow and voiding
performance for the given settings. An Innolot based solder paste can improve thermal cycling reliability performance
under certain conditions. We recommend Heraeus F640IL Innolot in combination with Al-IMS or Cu-IMS Boards. Vacuum
soldering equipment can be used to achieve a lower void level. Solder paste with powder type 3 is recommended for
required stencil thickness and aperture size.

5.2 Stencil Design

For the metal defined land pattern as for LUXEON FX2 (see Figure 16), Lumileds internal testing has been conducted with
a stencil aperture of 90 % of the LED footprint area. For the LUXEON FX2, a stencil thickness of 120 µm (ca. 5 mil) with a
type 3 paste is recommended. The corner radius of stencil aperture should be selected according to paste particle size to
improve paste release.

Figure 16. Stencil aperture for solder mask defined design LUXEON FX2

For the metal defined land pattern Lumileds internal testing has been conducted with a stencil aperture of 94% of the LED
footprint area.

Figure 17. Stencil aperture for solder mask defined design for LUXEON FX2 Plus

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 19
 5.3 Pick and Place Nozzle
The LUXEON FX2 is packed in a tape and reel with the light emitting surface facing upwards. Automated pick and place
equipment provides the best handling and placement accuracy for the LUXEON FX2-LED.

Lumileds recommends taking the following general pick and place guidelines into account:

1. The pick-up area is defined in Figure 18.

2. The nozzle tip should be clean and free of any particles since this may interact with the top surface coating of the
LED during pick and place.
3. During setup and the first initial production run, it is good practice to inspect the top surface of the LEDs under a
microscope to ensure that there are no accidentally damaged by the pick and place nozzle.
4. To avoid any mechanical overstress, it is a good choice to use soft material for pickup. Rubber nozzles are available
from various suppliers.
5. Ceramic nozzle can be used as low mass nozzles.
6. Lower Z-axis velocity at the point of board contact to avoid LED damage.

Figure 18. Pick-up position for LUXEON FX2 Plus LED

Since LUXEON FX2 has no primary optics or lens which can act as a mechanical enclosure protection for the LED chip, the
pick-up and placement force applied to the top of the package should be minimized and kept well controlled.

Picking the component out of the carrier tape should be performed from a defined height position and should not apply
forces to the component and carrier tape, as this may damage the component. The LUXEON FX2 is packed in a recess of
the carrier tape, and the nozzle geometry must be selected accordingly to not get in contact with carrier tape (see Figure 19).

Figure 19. Pick-up from carrier tape

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 20
 For the LUXEON FX2, a standard pick and place nozzle can be used, as shown in Figure 20a, 20b and 20c.

Figure 20a. ASM Siplace nozzle recommendation for LUXEON FX2

Figure 20b. Alternative ASM Siplace nozzle recommendation for LUXEON FX2

Figure 20c. Yamaha nozzle recommendation for LUXEON FX2

Table 6. ASM Siplace nozzle recommendation for LUXEON FX2

STANDARD NOZZLE (ORDER CODE) 03054253-02

Supplier ASM Siplace ASM Siplace (alternative) Yamaha
Nozzle form Rectangular Rectangular Rectangular
Material: Housing / Tip Vectra/Ceramic ESD able Vectra/Ceramic ESD able Vectra/Ceramic ESD able
P&P Head 4004 2033 CPP 302A
Name Nozzle Type 4004 Nozzle Type 2033 Nozzle Type 302A

A = 1.7 x 1.2 A = 0.9 x 0.5 A=1.7x0.9

Measurements [mm] a = 1.3 x 0.7 a = 0.7 x 0.3 a=1.4x0.6
L = 9.4 L = 16 L=7.5

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 21
 Figure 21 and Figure 22 show the standard pick and place nozzles from different SMT machine vendors, which can be used
to handle the LUXEON FX2 Plus.

Figure 21. ASM Siplace nozzle recommendation for LUXEON FX2 Plus

Table 7. ASM Siplace nozzle recommendation for LUXEON FX2 Plus

STANDARD NOZZLE (ORDER CODE) 03054923-02

Supplier ASM Siplace
Nozzle form Rectangular
Material: Housing / Tip Vectra A230/TPU ESD able
P&P Head 2033 CPP
Name Nozzle Type 2033
Measurements [mm] A = 2.2 x 1.6 , a = 1.7 x 1.1, L = 14

Figure 22. Juki machine nozzle recommendation for LUXEON FX2 Plus

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 22
 5.4 Placement Force
In order to avoid any damage of the LED and minimize squeeze-out of solder paste, placement process needs to be tightly
controlled. Lumileds recommends using low placement forces or a Z-height controlled placement during the pick and
place process. The force during pick and place should not exceed 2.0 N. An additional large dynamic peak force occurs if
the LED is placed with high Z-axis velocity at the point of touching the board and if the nozzle mass is high. Under worst
case conditions, the LED can be damaged. For example, if large particles are underneath the LED (see Figure 23). Lower
the Z-axis velocity if needed.

Figure 23. LED touching the board during pick and place can worst case damage the LED

5.5 Feed System

Pick and place machines are typically equipped with special pneumatic or electric feeders to advance the tape, that
contains the LEDs. The indexing step in the pick and place process may cause some LEDs to accidentally jump out of the
pocket tape or may cause some LEDs to get misaligned inside the pocket tape, resulting in pick-up errors. Depending on
the feeder design, minor modifications to the feeder can substantially improve the overall pick and place performance of
the machine and reduce/eliminate the likelihood of scratch or damage to the LEDs. The pick-up position should be right
after the cover tape peel off. Do not leave index positions uncovered between peel off and pick position. This will prevent
the LEDs from tilting over or jumping out when indexing. The cover tape peeling angle, relative to the tape, should be small
to reduce the vertical pulling force during indexing (see Figure 24).

Figure 24. Pick position and cover tape peeling

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 23
 5.6 Reflow Profile
The LUXEON FX2-LED is compatible with standard surface-mount and lead-free reflow technologies. This greatly simplifies
the manufacturing process by eliminating the need for adhesives and epoxies. The reflow step itself is the most critical
step in the reflow soldering process and occurs when the boards move through the oven and the solder paste melts,
forming the solder joints. To form good solder joints, the time and temperature profile throughout the reflow process
must be well controlled. A temperature profile consists of three primary phases:

1. Preheat: the board enters the reflow oven and is warmed up to a temperature lower than the melting point of the
solder alloy.
2. Reflow: the board is heated to a peak temperature above the melting point of the solder, but below the temperature
that would damage the components or the board.
3. Cool down: the board is cooled down rapidly, allowing the solder to freeze, before the board exits the oven.

As a point of reference, the melting temperature for SAC 305 is 217 °C, and the minimum peak reflow temperature is
235 °C.

Lumileds successfully utilized the reflow profile in Figure 25 and listed in Table 8 for LUXEON FX2.

Figure 25. Reflow profile definition according to JEDEC J-STD-020E

Table 8. Temperature measurement methods

PROFILE FEATURE TYPICAL VALUE MAXIMUM ACC.TO JEDEC J-STD-020E

Preheat Minimum Temperature (Tsmin) 150 °C 150 °C

Preheat Maximum Temperature (Tsmax) 200 °C 200 °C

Preheat Time (tsmin to tsmax) 100 seconds 60 to 120 seconds

Ramp-Up Rate (Tsmax to Tp) 2 °C / sec. avg. 3°C / second

Liquidus Temperature (TL) 217 °C 217 °C

Time Maintained Above Temperature TL (tL) 60 seconds 120 seconds

Peak/Classification Temperature (Tp) 240 °C 260°C

Time within 5°C of Actual Peak Temperature (tp) 20 seconds 30 seconds

Maximum Ramp-Down Rate (Tp to TL) 2.5 °C/sec. avg. 6°C/second

Time 25°C to Peak Temperature 310 seconds 480 seconds

Nitrogen Atmosphere (O2) <1000ppm

Note: All temperatures refer to the application Printed Circuit Board (PCB), measured on the surface adjacent to the package body.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 24
 Things to watch for after reflow should include:
1. Solder voids — perform x-ray inspection
2. Solder bridge between anode and cathode
3. Solder balling
4. Any visible damage, tilt or misplacement of LED
5. Any contamination on light emitting area — this may impact the light output extraction or cause color shift
6. Functional test (open/short)
7. Current test, e.g. Vf at 1 mA ≥ 2.0 V

5.7 Reflow Accuracy

Lumileds performed tests for position accuracy after reflow (see Figure 26 and Table 9). Results may vary based on printed
circuit board quality and used assembly process.

Figure 26. L1 and L2 tolerance definition. Exemplary cross section of LUXEON FX2 Plus

Table 9. Dimension and placement tolerances for LUXEON FX2 Plus

ITEM DESCRIPTION MAXIMUM VALUE (5σ) TYPICAL VALUE

A L1: Optical center to back-side metal X/Y ±50 µm

B L1: Total thickness Z ±75 µm
C L2: Optical center to L2 fiducial, X/Y ±50 µm
D L2: Optical center to L2 fiducial, Z ±75 µm
Note: Typical values given are derived from sample based assembly tests performed at Lumileds and calculated for 5 Sigma.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 25
 5.8 Board Handling and Bending
The LED package handling precaution, as described in section 2.2 “Component Handling”, must also be applied when
handling LED assemblies. For example, bending of a PCB is a common handling problem, typically seen on large boards. A
printed circuit board may warp after reflow when layers with different CTE (coefficient of thermal expansion) are applied to
the top and bottom of the boards. If the PCB is subsequently secured to a flat surface, a vertical force is applied to the LED
package (see Figure 27).

Any deformation by mounting the board and screwing it onto a heatsink or by de-paneling, like punching-off or breaking-
off, should be kept to minimum. As a general guideline, it should be at most 2 mm of vertical deflection for every 90mm
of FR4 PCB length. The guideline in Figure 28 should be maintained to prevent the sapphire chip, used in the LED, from
cracking and causing device failure. Reference AEC-Q200-005 for board bending test preparation.

This board bending test does not apply to solder joint reliability, as the ability of the solder joint to withstand this stress
(elongation) depends on the footprint layout, solder joint thickness, solder voiding and the type of solder paste used.

Figure 27. Maximum PCB bending guideline to prevent damage to the LED package

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 26
 5.9 Packing of Assembled LUXEON FX2 Module
Finished boards must be protected against damage during transport. It is recommended to use a customized tray
package, which is designed to hold the PCBs during transport (see Figure 28).

Here some general rules of best practice tray design:

1. Design the tray to avoid accidently touching the LED by manual handling. Ideally, the tray only allows one way to hold
the assembly. If there are several ways to put assemblies into the tray or take them out, a strict operator discipline
and clear instruction on how to safely handle the assemblies is needed.
2. It must be designed in a way that no force from the tray or packing material is applied to the LED.
3. In a stack of multiple trays, the PCB should also be secured from the top. This can be done by bottom structures of
the next tray which is put on top of the stack.
4. The tray should also protect the LED against movement and shaking/vibrations during transport.

Figure 28. Schematic of a good tray design. The LEDs are protected against movement and no forces are applied to the LEDs.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 27
6. Interconnect Reliability Parameters
The reliability of board interconnect under thermal cycling and thermal shock condition is mainly determined by thermal
expansion of used materials. The LUXEON FX2 package is made of AlN which has a low CTE of ~4 ppm (coefficient of
thermal expansion). The CTE mismatch between LED package and printed circuit board will lead to mechanical stress and
cause solder fatigue or solder cracking. To achieve highest possible reliability the CTE of the board material should be as
similar to the LED package as possible. Table 10 shows commonly used materials and their CTE.

Table 10. CTE of Common board substrate materials

COEFFICIENT OF THERMAL EXPANSION (CTE)

MATERIAL
±2.0 TO ±5.0 [1]

Sapphire (LED chip) 5-6 ppm

Solder SAC305 19-22 ppm
Copper 16.5 ppm
FR4 12-17 ppm*
Aluminium 5052 23.1 ppm
Aluminium CTE II 19 ppm
AlN 4 ppm
Al203 6-8 ppm
*Depending on laminate vendor, prepreg type, and fiber orientation

Also, the mechanical properties of solder material and solder thickness have an impact on interconnect reliability. Using a
ductile material and increasing the bond line thickness will increase solder joint reliability.

The pad design of LUXEON FX2 has shown increased interconnect reliability, compared to the design of LUXEON FX2 Plus.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 28
7. JEDEC Moisture Sensitivity Level
JEDEC has defined eight levels for moisture sensitivity, as shown in Table 11.

Table 11. JEDEC moisture sensitivity levels

SOAK REQUIREMENTS
FLOOR LIFE
LEVEL STANDARD ACCELERATED EQUIVALENT 1

TIME CONDITIONS TIME CONDITIONS TIME CONDITIONS

1 Unlimited ≤ 30 °C / 85% RH 168 Hours +5 / -0 85 °C / 85% RH

2 1 Year ≤ 30 °C / 60% RH 168 Hours +5 / -0 85 °C / 60% RH

2a 4 Weeks ≤ 30 °C / 60% RH 696 Hours +5 / -0 30 °C / 60% RH 120 Hours +1 / -0 60 °C / 60% RH

3 168 Hours ≤ 30 °C / 60% RH 192 Hours +5 / -0 30 °C / 60% RH 40 Hours +1 / -0 60 °C / 60% RH

4 72 Hours ≤ 30 °C / 60% RH 96 Hours +2 / -0 30 °C / 60% RH 20 Hours +5 / -0 60 °C / 60% RH

5 48 Hours ≤ 30 °C / 60% RH 72 Hours +2 / -0 30 °C / 60% RH 15 Hours +5 / -0 60 °C / 60% RH

5a 24 Hours ≤ 30 °C / 60% RH 48 Hours +2 / -0 30 °C / 60% RH 10 Hours +5 / -0 60 °C / 60% RH

Time on
6 30 °C / 60% RH TOL 30 °C / 60% RH
Label (TOL)

*Depending on laminate vendor, prepreg type, and fiber orientation

The LUXEON FX2-LED has a JEDEC moisture sensitivity level of 1. This is the best level in the industry and within the JEDEC
J-STD-020D.1 standard. The customer no longer needs to be concerned about bake out times and floor life. No bake out
time is required for a moisture sensitivity level of 1.

Moisture sensitivity level 1 allows the device to be reflowed three times under the specifications as described in the
respective LUXEON FX2 datasheets.

8. Product Packaging Consideration – Chemical

Compatibility
The package contains a silicone overcoat to protect the LED chips and extract the maximum amount of light. As with most
silicones used in LED optics, care must be taken to prevent any incompatible chemicals from directly or indirectly reacting
with the silicone.

The silicone overcoat is gas permeable. Consequently, oxygen and volatile organic compound (VOC) gas molecules can
diffuse into the silicone overcoat. VOCs may originate from adhesives, solder fluxes, conformal coating materials, potting
materials and even some of the inks that are used to print the PCBs. Some VOCs and chemicals react with silicone and
produce discoloration and surface damage. Other VOCs do not chemically react with the silicone material directly but
diffuse into the silicone and oxidize during the presence of heat or light. Regardless of the physical mechanism, both cases
may affect the total LED light output. Since silicone permeability increases with temperature, more VOCs may diffuse into
and/or evaporate out from the silicone.

Careful consideration must be given to whether the LEDs are enclosed in an “air tight” environment or not. In an “air tight”
environment, some VOCs that were introduced during assembly may permeate and remain in the silicone overcoat.

Under heat and “blue” light, the VOCs inside the silicone overcoat may partially oxidize and create a silicone discoloration,
particularly on the surface of the LED where the flux output is the highest. In an air rich or “open” air environment, VOCs
have a chance to leave the area (driven by the normal air flow). Transferring the devices, which were discolored in the
enclosed environment back to “open” air, may allow the oxidized VOCs to diffuse out of the silicone overcoat and may
restore the original optical properties of the LED.

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 29
 Determining suitable threshold limits for the presence of VOCs is very difficult since these limits depend on the type of
enclosure used to house the LEDs and the operating temperatures. Also, some VOCs can photo-degrade over time.

Table 12 provides a list of commonly used chemicals that should be avoided as they may react with the silicone material.
Note that Lumileds does not warrant that this list is exhaustive since it is impossible to determine all chemicals that may
affect LED performance.

The chemicals in Table 12 are typically not directly used in the final products that are built around the LEDs. However,
some of these chemicals may be used in intermediate manufacturing steps (e.g. cleaning agents). Consequently, trace
amounts of these chemicals may remain on sub-components, such as heatsinks. Lumileds, therefore, recommends the
following precautions when designing your application:

When designing secondary lenses to be used over an LED, provide a sufficiently large air-pocket and allow for “ventilation”
of this air away from the immediate vicinity of the LED. Use mechanical means of attaching lenses and circuit boards as
much as possible. When using adhesives, potting compounds and coatings, carefully analyze its material composition and
do thorough testing of the entire fixture under High Temperature Over Life (HTOL) conditions.

Table 12. List of commonly used chemicals that may damage the silicone overcoat of the LED

CHEMICAL NAME TYPICAL USE

Hydrochloric Acid Acid
Sulfuric Acid Acid
Nitric Acid Acid
Acetic Acid Acid
Sodium Hydroxide Alkali
Potassium Hydroxide Alkali
Ammonia Alkali
MEK (Methyl Ethyl Ketone) Solvent
MIBK (Methyl Isobutyl Ketone) Solvent
Toluene Solvent
Xylene Solvent
Benzene Solvent
Gasoline Solvent
Mineral spirits Solvent
Dichloromethane Solvent
Tetracholoromethane Solvent
Castor oil Oil
Lard Oil
Linseed Oil Oil
Petroleum Oil
Silicone Oil Oil
Halogenated Hydrocarbons (containing F, Cl, Br elements) Misc.
Rosin Flux Solder Flux
Acrylic Tape Adhesive

AB183 LUXEON FX2 Application Brief 20230417 ©2023 Lumileds Holding B.V. All rights reserved. 30
About Lumileds
Companies developing automotive, mobile, IoT and illumination lighting applications need a partner who can collaborate with
them to push the boundaries of light. With over 100 years of inventions and industry firsts, Lumileds is a global lighting solutions
company that helps customers around the world deliver differentiated solutions to gain and maintain a competitive edge. As the
inventor of Xenon technology, a pioneer in halogen lighting and the leader in high performance LEDs, Lumileds builds innovation,
quality and reliability into its technology, products and every customer engagement. Together with its customers, Lumileds is
making the world safer, better and more beautiful—with light.

To learn more about our lighting solutions, visit lumileds.com.

©2023 Lumileds Holding B.V. All rights reserved. Neither Lumileds Holding B.V. nor its affiliates shall be liable for any kind of loss of data or any other damages,
LUXEON is a registered trademark of the Lumileds direct, indirect or consequential, resulting from the use of the provided information and data. Although Lumileds
Holding B.V. in the United States and other countries. Holding B.V. and/or its affiliates have attempted to provide the most accurate information and data, the materials
and services information and data are provided “as is,” and neither Lumileds Holding B.V. nor its affiliates
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B.V. and its affiliates reserve the right to make changes without notice. You as user agree to this disclaimer and
user agreement with the download or use of the provided materials, information and data. A listing of Lumileds
product/patent coverage may be accessed at lumileds.com/patents.
AB183 LUXEON FX2
Application Brief 20230417