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Is the material of the ceramic substrate a great potential for development?

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Now, with the domestic and international LED careers in the direction of high power, high density, high power, etc., it can be seen from 2017 to 2018 that the overall domestic LED has a rapid pause, the power is getting bigger and bigger, and the development function is superior. Heat-dissipating materials have become an urgent need to deal with LED heat dissipation problems. In general, the LED luminous power and operating life will decrease as the junction temperature increases. When the junction temperature reaches above 125 °C, the LED will fail. In order to keep the LED junction temperature at a lower temperature, it is necessary to use a high thermal conductivity, low thermal resistance heat sink substrate material and a reasonable packaging process to reduce the overall package thermal resistance of the LED.
At present, the commonly used substrate materials are Si, metal and metal alloy materials, ceramics and composite materials. Their thermal shortening coefficient and thermal conductivity are shown in the following table. In the meantime, the Si material cost is high; the intrinsic conductivity of the metal and metal alloy materials, the thermal shortening coefficient is not matched with the chip material, and the ceramic material is difficult to process, etc., and it is difficult to meet the various functions of the high-power substrate together.
Since the power LED packaging technology has been developed, the available heat dissipation substrates mainly include epoxy resin copper-clad substrates, metal-based copper-clad substrates, metal-based composite substrates, and ceramic copper-clad substrates.

Epoxy copper clad substrates are the most commonly used substrates in conventional electronic packages. It plays the role of support, conduction and insulation. Its main characteristics are: low cost, high moisture absorption resistance, low density, easy processing, easy to complete micro-graphic circuits, suitable for a wide range of consumption. However, since the base material of FR-4 is epoxy resin, the thermal conductivity of organic materials is low and the high temperature resistance is poor. Therefore, FR-4 cannot be adapted to high-density, high-power LED package requirements, and is generally only used in low-power LED packages.


<a href='/' style='color:blue;'>ceramic substrate</a>



The metal-based copper-clad substrate is a new type of substrate that appears after FR-4. The copper foil circuit and the polymer insulating layer are directly bonded by a thermally conductive bonding material and a metal and a base having a high thermal conductivity. The thermal conductivity is about 1.12 W/m·K, and the FR-4 is compared. There is a big improvement. Due to its excellent heat dissipation, it has become the most popular product in the market for high-power LED heat-dissipating substrates. However, it also has its inherent disadvantages: the thermal conductivity of the polymer insulation layer is low, only 0.3 W/m·K, which causes the heat not to pass directly from the chip to the metal base; the heat of the metal Cu and Al A large shortening factor may result in a more severe thermal mismatch problem.
The most representative material of the metal matrix composite substrate is aluminum silicon carbide. Aluminum silicon carbide is a metal matrix composite that separates the low shortening coefficient of SiC ceramics from the high thermal conductivity of metal Al. It combines the strengths of two materials, with low density, low heat shortening coefficient, high thermal conductivity, and high stiffness. A series of excellent features. The thermal shortening factor of AlSiC can be adjusted by modifying the SiC content to match the thermal shortening factor of the adjacent material to minimize the thermal stress of both.
Ceramic substrate materials are mainly Al2O3, aluminum nitride, SiC, BN, BeO, Si3N4, etc. Compared with other substrate materials, ceramic substrates have the following characteristics in mechanical properties, electrical properties, and thermal properties:
(1) Mechanical function. Mechanical strength, can be used as a support member; good processability, high dimensional accuracy; surface lubrication, no microcracks, tortuosity, etc.
(2) Thermal properties. The thermal conductivity is large, the thermal shortening coefficient is matched with the chip materials such as Si and GaAs, and the heat resistance is excellent.
(3) Electrical properties. The dielectric constant is low, the dielectric loss is small, the insulation resistance and the insulation are high, and the function is stable under high temperature and high humidity conditions, and the reliability is high.
(4) Other properties. Good chemical stability, no hygroscopicity; oil and chemical resistance; non-toxic, pollution-free, α-ray emission is small; crystal structure is stable, it is not easy to change within the operating temperature range; raw material resources are abundant.
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