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Application Note

Light Emitting Diode

This document contains tentative information; the contents may change without notice.

(SE-AP00019C)

Oct. 6, 2017

1. Overview

COBs have been recently introduced in LED lighting applications and expanded into the market.

It is very necessary to consider heat dissipation to design the lighting fixture installing COBs.

A single COB can achieve a high output power. Moreover, the design of COBs allows the heat to

be concentrated in a narrow space, because the multiple dice are closely mounted. Thus, it is

necessary to verify the heat dissipation when designing the lighting fixture, not to degrade the

performance by heat (e.g. decrease in the luminous flux according to the temperatures) or not to

deteriorate the reliability performance.

This document shows the evaluation results of the heat dissipation performance according to the

adhesion strength of COBs and the housing (heat sink).

2. Relation of the Tightening Torque and the Heat Dissipation

Nichia recommends that the specific holder should be used to fix a COB to the housing (e.g. heat

sink). Enhancing the adhesion strength of COBs to the housing can result in better heat

dissipation performance. In general, screws are used to fix the holder; thus, the tightening torque

significantly affects the adhesion strength.

We evaluated the heat dissipation performance according to the tightening torque.

2-1. Evaluation Method

A COB waattached to the heat sink with holders. We changed the tightening torque for the screws

to evaluate the relation of the torque and Tj (cf. Figure 1). We used NSCWL036A (5.8W) and

NSCWJ216A (34.8W) for the evaluation.

After attaching the COBs to the heat sink as seen in Fig.1, each COB was operated at the rated

power. We measured the Tj after 30 minutes when the heat was saturated, and compared the Tj

according to the tightening torque.

Figure 1 Evaluation Method

Condition 1 Condition 2

Overview

COB Model

NSCWL036A NSCWJ216A

Power

5.8W (Rated Power) 34.8W (Rated Power)

Holder

Screw

Heat Sink

17mm×98mm×L100mm (Heat Resistance: 3.0℃/W) 60mm×110mm×L100mm (Heat Resistance: 1.3℃/W)

Heat Dissipating Seat

Made by Tyco Electronics Corporation [TypeN 213446-1]

M2.6 (Pan Head Screw, no washer)

t=0.25mm , Thermal Conductivity: 1.0W/mK

Fixed with different tightnening torque

Made by Tyco Electronics Corporation