Research on the Influence of LED Chip Distribution on Thermal Performance

LED lighting, due to significant energy savings, is considered the next generation of lighting technology. The LED is a cold light source, and its spectrum does not contain the infrared part. At present, the luminous efficiency of the LED is only 20%, that is, more than 80% of the electric energy is converted into heat. If the heat can not be effectively dissipated, the temperature of the chip will rise, which will lead to a decrease in light efficiency, aggravation of light decay, and burning of the chip in serious cases. The heat dissipation of the LED chip is a major unsolved problem in the development of LED lighting.

The heat dissipation process of the LED chip is not complicated. It is only a series of heat conduction process plus convection heat transfer process. The temperature range is not high. It belongs to normal temperature heat transfer. The heat conduction process inside can completely solve the three-dimensional heat conduction differential equation by computer-specific software. Analyze the heat conduction process in the LED chip, the heat conduction process in the heat sink, and the convective heat transfer of the heat sink surface, and analyze the main heat resistance in the whole heat transfer process. What causes the problem, a very clear solution can be obtained. Make people aim.

However, the current LED heat dissipation and the heat dissipation of similar semiconductor chips lack this basic and guiding research. Even if someone does, it is not known. As a result, today's LED cooling technology is like the Spring and Autumn Warring States era, the use of heat pipes, and even the use of loop heat pipes. This paper only studies the analysis of its influence on heat dissipation from the different distribution of LED chips, which will play a guiding role in the design and manufacture of LED chips.

1. Calculate the simulated model

figure 1

As shown in Figure 1, one side of the aluminum heat sink is provided with nine 1×1mm, 1w chips, and a 0.1mm thick thermal conductivity of 4w/(m·k) of insulating heat conduction layer, the total area of ​​the ribs. For m2, the air convection heat transfer coefficient is = 6 w/(m2·k), and the thermal conductivity of aluminum is 202 w/(m · k). In order to simplify the calculation, the heat conduction problem in the ribs is not considered, and the convection heat transfer surface of the fin heat dissipation surface is simplified to 65 × 65 mm and the convective heat transfer coefficient is 85 w / (m 2 · k). That is, an aluminum block (65×65×3 mm) with a convective heat transfer surface (=85w/(m2·k)) on one side and 9 chips (1×1 mm, 1w) on the other side is used when the chip pitch is different. Its internal temperature field.

Solve the equation:

It is a three-dimensional steady-state thermal differential equation, usually called Laplace equation. Solve with dedicated calculation software.

2, the calculation results

Figure 2 shows the temperature distribution of the over-center point of the metal surface of the heat sink with different chip spacings.

The chip spacing L is 1mm, 2.5mm, 5mm, 7.5mm, 10mm, 15mm, 20mm, 25mm, 30mm.

When L=1mm, that is, 9 LED chips are grouped together without any gap between them.

Table 1 lists the temperature values ​​of the different chip spacings, the center point of the heat sink metal surface (ie, the highest temperature point) and the difference. The ambient temperature in the above calculation is 40 ° C (313 K).

3. Analysis

It can be clearly seen from Fig. 2 and Table 1: When 9 LED chips are grouped together (chip pitch L = 1 mm), the center point (the highest temperature at which the chip is placed) has the highest temperature, that is, the heat dissipation effect is the worst. . When the chip pitch is increased by 1.5 mm (L = 2.5 mm), the highest point temperature drops by 3.1 ° C, and when the chip pitch increases by 4 mm (L = 5 mm), the highest point temperature drops by 4.8 ° C. When the chip pitch is L = 7.5 mm, the highest point temperature drops by 5.6 °C. When the chip pitch is L = 10 mm, the temperature drops by 6.1 °C. When the chip pitch is L = 20 mm, the temperature drops by 7.2 °C. The temperature drop is significant within the spacing L = 10 mm.

4, the results

(1) The distribution of LED chips has a great influence on heat dissipation, and the LED chips should be dispersed.

(2) For 1×1mm, 1w LED chips, the chip pitch is preferably 5~10mm.