A new trend in LED heat dissipation - LED 矽 substrate package thermal conductivity

The use of germanium-based materials as LED package substrate technology has gradually been introduced into the LED industry from the semiconductor industry in recent years, and the greatest advantage of LED substrates using germanium materials is their excellent thermal conductivity.

Power LED packages developed in response to the needs of the LED lighting market, using currents from 150 mA, 350 mA, up to 700 mA or even 1 A, are used on 1 mm square LED chips, because current is converted into LED chips. The efficiency of light is only 30%, and 70% of the current will be converted into heat. If there is no good heat conduction method to conduct heat out of the LED chip, the LED chip will burn out, causing rapid light decay.

To solve the thermal conductivity of the LED package, it is necessary to adopt a low thermal resistance design from the structure, and at the same time, it has a light function in terms of size to meet the requirements of modern lamps. In order to meet the needs of LED packaging, traditional LED packaging must be revolutionized. In recent years, one of the most representative packages has been developed (as shown in Figure 1). The heat generated by the LEDs can be directly derived from the substrate and has a small function.
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Figure 1 Lightweight and thermally conductive LED package.


The theoretical formula for the calculation of thermal resistance is Rth = T / KA, where each parameter is defined as follows:

Rth: thermal resistance, the unit is K / W, that is, the temperature value generated when the current per watt (W) is passed into the LED chip;
T: thickness of the thermally conductive substrate (um);
K: thermal conductivity of the thermally conductive substrate (W/mK);
A: Heat transfer area (mm x mm).

Therefore, according to the thermal resistance calculation theory formula, how to select a substrate material which can have a high thermal conductivity and can be mass-produced under the fixed substrate thickness and the heat conduction area is the key to solving the heat conduction of the LED. In view of current industrial technology or mass production maturity, since both alumina (Al2O3) and bismuth (Si) have been widely used in electronic component substrates at the same time, it will become the industry's best choice for LED substrate materials.

Alumina is currently used in a large number of resistors, capacitors, mixed-film circuits, automotive electronics, and high-frequency component boards, while 矽 is used in semiconductor component manufacturing. Alumina is used in LED packaging because of its high insulation properties. Light and small components can be fabricated. However, because of the low thermal conductivity of the alumina material, the thermal resistance is 5.2 K/W when the thickness of the alumina substrate is 400 um. When a large current (700 mA) is applied to the LED wafer, The instantaneous temperature rise of 13 ° C will not be able to conduct heat immediately out of the LED chip. At this time, the LED chip will produce rapid light decay. Therefore, the high thermal resistance is a problem in which alumina is used as the LED substrate.

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