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Research Papers

Thermal Investigation and Placement Design of High-Brightness LED Array Package on PCB for Uniform Illuminance

[+] Author and Article Information
K. C. Yung1

Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SARmfkcyung@inet.polyu.edu.hk

H. Liem, H. S. Choy, W. K. Lun

Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR

1

Corresponding author.

J. Electron. Packag 133(1), 011006 (Mar 09, 2011) (14 pages) doi:10.1115/1.4003514 History: Received September 30, 2010; Revised January 14, 2011; Published March 09, 2011; Online March 09, 2011

This paper reports the thermal performance of a high-brightness light-emitting diode (LED) array package with a novel placement method on a printed circuit board (PCB). The precise heat transfer analysis and modeling using computational fluid dynamics (CFD) were performed according to the practical working conditions of the LED array. Emphasis was placed upon investigating how the temperature of the surface of LEDs changed in accordance with different placement methods. A significant drop in the surface temperature of the LEDs was found when the triangular and arithmetic spacing placement methods were used; hence, the overall heat dissipating capability of the LED array to the PCB was improved. By optimizing the placement design, the average surface temperature of the LED array achieved a decrease of about 20%, from 120°C to 100°C. The illuminance level of each placement design was measured and compared. Both CFD simulation and experimental results are provided to demonstrate the efficacy of the proposed approach for LED array thermal management.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

LED array package. (a) Cross sectional view of a high-brightness LED in its package, (b) schematic of a LED array control circuit in series, (c) typical representative spatial radiation pattern for a LED, and (d) typical polar radiation pattern for a LED.

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Figure 2

Schematic of (a) a typical mutilayer PCB, (b) a double sided FR4 PCB, and (c) a single-layer metal core laminate

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Figure 3

Schematic of the experimental setup for (a) a unit LED PCB setup, (b) study cases for PCB, (c) parameters for LED array illuminance measurement, and (d) illuminance profile for a LED array–PCB system

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Figure 4

An algorithm for LED square array placement

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Figure 5

An algorithm for LED hexagonal array placement

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Figure 6

An algorithm for LED triangular array placement

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Figure 7

Change in case temperature of LED at a constant current of 0.7 A. (a) Experimental setup, (b) transient case temperature after switching on and off, (c) IR imaging on the case temperature of LED, and (d) measured average temperatures for seven data points.

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Figure 8

Normalized electroluminescence (EL) spectra from a high power white GaN/InGaN LED for different currents indicated. The inset shows the amplitudes of the three emission peaks at various currents.

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Figure 9

LED case temperature at different currents

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Figure 10

Effect of PCB material on the heat dissipation of two LEDs with 2 mm spacing at a constant current of 0.3 A. (a) LEDs held in series on a PCB at room temperature without current supply initially, (b) LEDs on an FR4 PCB, (c) LEDs on a metal core PCB, and (d) simulated thermal profile for a 3×3 LED array on FR4 or metal core PCB at a current of 0.3 A.

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Figure 11

Temperature change of LED when placed along a diagonal line of a PCB. (a) Simulated thermal profile results at PCB center and corner region and (b) measured case temperatures for different point locations.

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Figure 12

Temperature change between two LEDs for different spacing distances. (a) Simulated thermal profile results on PCB for spacing distance of 0.5 mm and 4 mm, respectively, and (b) measured case temperatures for different point locations.

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Figure 13

Effect of spacing for different grid array patterns. (a) Square, hexagonal, and triangular placement methods, (b) average case temperature against each LED number, (c) simulated thermal profiles on the top and section views, and (d) contour plot and 3D plot of illuminance.

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Figure 14

Effect of spacing on case temperature and illuminance for different spacing patterns of a LED array–PCB system. (a) Uniform spacing, (b) uniform spacing at center and two ends, and (c) arithmetic spacing.

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