LED process design includes chip design and chip packaging. At present, the packaging technology of high-power LED and its heat dissipation technology are the hotspots of social research today. The process flow of high-power LED packaging is relatively simple, but the actual process is very complicated. And LED packaging technology directly affects the service life of LED. Therefore, in the process of high-power LED packaging, many factors should be considered, for example, light, heat, electricity, machinery and many other factors. The optical aspect must consider the light decay of high-power LEDs, the thermal aspect must consider the heat dissipation of high-power LEDs, the electrical aspect must consider the design of the power supply of high-power LEDs, and the mechanical aspect must consider the LED packaging form Wait.
1 High-power LED packaging requirements and key technologies
(High power) LED has the advantages of long life, low pollution, low power consumption, energy saving and impact resistance. Compared with traditional lighting fixtures, (high-power) LEDs not only have good monochromaticity, high optical efficiency and strong light efficiency, but also can meet different needs with high color rendering index. Nevertheless, the packaging process of high-power LEDs has strict requirements.
It is embodied in: ①low cost; ② maximum system efficiency; ③ easy replacement and maintenance; ④ multiple LEDs can be modularized; ⑤ simple requirements such as high heat dissipation coefficient.
According to various factors to be considered in high-power LED packaging technology, several points are also proposed in the key packaging technology. mainly includes:
(1) In terms of heat dissipation of high-power LEDs: low thermal resistance package is considered. The LED chip is a solid-state semiconductor device, which is the core part of the LED light source. Because high-power LED chips vary in size, and the driving method is a constant current driving method. The electric energy can be directly converted into light energy, so the LED chip needs to absorb most of the input electric energy during the lighting process, and a large amount of heat will be generated during this process. Therefore, the heat dissipation technology for high-power LED chips is an important technology in the LED packaging process, and also a key problem that must be solved in the high-power LED packaging process.
(2) The heart of the LED is a semiconductor chip, one end of the chip is attached to a bracket, one end is the negative electrode, and the other end is connected to the positive electrode of the power supply. Therefore, the high light extraction package structure is also an important key technology in the high-power LED packaging process. In the process of LED chip lighting, during the emission process, due to the difference in the refractive index at the interface, it will cause the loss of photon reflection and the possible total reflection loss. gum.
This layer of transparent glue must have the characteristics of high light transmittance, high refractive index, good fluidity, easy spraying and good thermal stability. At present, the commonly used transparent adhesive layers are epoxy resin and silica gel.
2 LED package
With the development of science and technology, there are many kinds of LED packaging forms, including lead type packaging, surface mount chip packaging, chip on board direct packaging, and system packaging packaging.
The packaging of low-power LEDs generally adopts a pin-type LED package. Leaded LED packages are also relatively common. Ordinary light-emitting diodes are basically leaded packages. The heat of the pin-type LED package is dissipated from the negative lead frame to the PCB board, and the heat dissipation problem is also better solved. But there are also certain disadvantages, that is, the thermal resistance is large, and the service life of the LED is short.
Surface Mount SMT (SMT) is a new type of LED packaging method, which is a packaging technology that solders already packaged LED devices to a fixed position. The advantages of SMT packaging technology are strong reliability, easy automation, and good high-frequency characteristics. The SMT LED packaging form is the most popular SMD packaging process in the electronics industry today.
Chip on board (COB) LED packaging technology is a direct mounting technology, which is to directly stick the chip on the printed circuit board, then stitch the leads, and finally use organic glue to protect the chip and the lead. The COB process is mainly used in high-power LED arrays. Has a high degree of integration.
System-in-package (SIP) LED packaging technology is a technology developed in recent years.
It mainly meets the requirements of system portability and system miniaturization. Compared with other LED packages, SIP packages have the highest integration and relatively low cost. Multiple LED chips can be assembled in one package.
In the actual application process, according to the requirements of the experiment, the author adopted the form of SMT package. Because in the process of high-power LED packaging, the heat dissipation of high-power LED should be considered, I used the traditional method of using aluminum substrate heat dissipation. We have found through practical applications that SMT packaging technology is in line with actual heat dissipation requirements. The specific physical picture of aluminum substrate heat dissipation is shown in Figure 1.
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