AB171 LUXEON SunPlus 35 Line for Horticulture Application Brief 20161110 ©2016 Lumileds Holding B.V. All rights reserved.

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3. PCB Design Guidelines for the LUXEON Emitter

The LUXEON emitter is designed to be soldered onto a Printed Circuit Board (PCB). To ensure optimal operation, the PCB

should be designed to minimize the overall thermal resistance between the LED package and the heat sink.

3.1 PCB Footprint and Land Pattern

The recommended PCB footprint design for the LUXEON emitter is shown in Figure 2. In order to ensure proper heat

dissipation from the emitter electrodes to the PCB, it is best to extend the top copper layer of the PCB beyond the

perimeter of the LUXEON emitter by at least 3mm (see Section 4).

3.2 Surface Finishing

Lumileds recommends using a high temperature organic solderability preservative (OSP) or electroless nickel immersion

gold (ENIG) plating on the exposed copper pads.

3.3 Minimum Spacing

Lumileds recommends a minimum edge to edge spacing between LUXEON emitters of 0.5mm. Placing multiple LUXEON

emitters too close to each other may adversely impact the ability of the PCB to dissipate the heat from the emitters and

may cause accidental shorts between the metal stubs on the side of neighboring LUXEON emitters.

Figure 3. Top copper trace patterns showing the maximum (optimized and standard) and minimum top side metallization.

For the maximum copper design, one can optimize the copper trace pattern to take into account that the heat is mainly

dissipated from the cathode pad. There is no need to have large copper area around the anode.

4. Thermal Management

The overall thermal resistance between a LUXEON emitter and the heat sink is strongly affected by the design and material

of the PCB on which the emitter is soldered. On FR4 based PCB, the following general guidelines will yield optimum thermal

performance:

– thicker top copper layer, for e.g. 2 oz versus 1 oz copper

– at least 3mm of top copper layer extending outside the LED package. Table 1 shows the result of the thermal

resistance from junction to heat sink using two boards with different copper areas surrounding the LED package

(Figure 3)

– top copper trace pattern layout. Figure 3 shows the optimized max copper (optimized) layout versus standard max

copper (standard) layout. The former will yield lower board thermal resistance

Note that using double sided FR4 board will not yield noticeable improvement in the board thermal resistance.