Analysis of the heat dissipation problem of high-power LED bulbs

 Nowadays , LED white light products are gradually being used in various fields. While people are enjoying the amazing pleasure brought by high-power LED white light, they are also worried about various practical problems! First of all, from the nature of high-power LED white light itself. High-power LED still has problems such as poor uniformity of light emission, short life of sealing materials, and especially the problem of heat dissipation of LED chips , which is difficult to be solved well, and the expected application advantages of white light LED cannot be brought into play.

　　Secondly, from the perspective of the market price of high-power LED white light, today's high-power LED is still a noble white light product, because the price of high-power products is still too high, and the technology is still to be improved, so high-power white light LED products are not available to everyone who wants to use them. The following is a breakdown of the related issues of high-power LED heat dissipation.

　　In recent years, with the efforts of industry experts, the following improvement plans have been proposed for the heat dissipation problem of high-power LED chips: 1. Increase the light output by increasing the area of ​​the LED chip. 2. Use several small-area LED chips for packaging. 3. Change the LED packaging materials and fluorescent materials. So can the heat dissipation problem of high-power LED white light products be completely improved through the above three methods? In fact, it is remarkable! First of all, although we increase the area of ​​the LED chip to obtain more luminous flux (the number of light beams passing through a unit area per unit time is the luminous flux, unit ml) and hope to achieve the white light effect we want, is the heat dissipation problem of high-power LED white light really unsolvable? Of course not. In response to the negative problems caused by simply increasing the chip area, LED white light industry has improved the surface of the high-power LED chip by improving the electrode structure and flip chip structure and using several small-area LED chips for packaging to achieve a luminous efficiency of 60lm/W with high luminous flux and low heat dissipation.

　　In fact, there is another way to effectively improve the heat dissipation problem of high-power LED chips. That is to replace the previous plastic or plexiglass with silicone resin for its white light packaging material. Replacing the packaging material can not only solve the heat dissipation problem of LED chips, but also increase the life of white light LEDs. It really kills two birds with one stone. What I want to say is that almost all high-power white light LED products such as high-power LED white light should use silicone resin as the packaging material. Why must silicone be used as the packaging material in high-power LEDs now? Because the absorption rate of silicone for light of the same wavelength is less than 1%. However, the absorption rate of epoxy resin for 400-459nm light is as high as 45%, and it is easy to cause serious light decay due to aging caused by long-term absorption of this short-wavelength light.

　　Of course, in actual production and life, there will be many problems such as heat dissipation of high-power LED white light chips, because the more widely people use high-power LED white light, the more in-depth and difficult problems will arise! The characteristic of LED chips is that they generate extremely high heat in a very small volume. The heat capacity of the LED itself is very small, so the heat must be conducted out at the fastest speed, otherwise it will generate a very high junction temperature. In order to lead the heat out of the chip as much as possible, people have made many improvements to the chip structure of the LED. In order to improve the heat dissipation of the LED chip itself, the most important improvement is to use a substrate material with better thermal conductivity. The thermal resistance of Cree's LED is at least twice that of other companies because it uses silicon carbide as a substrate.

　　Even if the heat resistance between the chip and the packaging material can be solved, if the heat dissipation effect from the package to the PCB is not good, it will also cause the temperature of the LED chip to rise and the luminous efficiency to decrease. Therefore, in order to solve this problem, Panasonic has designed round, linear, and planar white light LEDs with PCB substrates since 2005 to overcome the problem of heat dissipation interruption between the package and the PCB.

　　Therefore, in the face of increasing current, how to increase heat resistance is also an urgent problem to be overcome at this stage. From various aspects, in addition to the problem of the material itself, it also includes the heat resistance from the chip to the packaging material, the thermal conductivity structure, the heat resistance from the packaging material to the PCB board, the thermal conductivity structure, and the heat dissipation structure of the PCB board, etc. These all need to be considered as a whole.