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Ceramic substrate is a relatively promising material

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Now, with the domestic and international LED industry to the direction of high power, high density, high power, etc., from 2017 to 2018 can see the ceramic substrate, the overall domestic LED has a rapid stagnation, the power is also growing, the development function is superior The heat dissipation material has become a top priority in dealing with LED heat dissipation. In general, LED luminous power and operating life will decrease with the addition of junction temperature. When the junction temperature reaches above 125 °C, the LED will eventually 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 cost of Si material is high; the intrinsic conductivity and heat shortening coefficient of metal and metal alloy materials are not matched with the chip material; the defects such as difficult processing of ceramic materials are difficult to satisfy the various functions of high-power substrates.
Since the power LED packaging technology has been unfolded, 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 widely used substrates in conventional electronic packaging. 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 comply with high-density, high-power LED package requirements, and is generally only used in low-power LED packages.
The metal-based copper-clad substrate is a new type of substrate that is presented 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, and the thermal conductivity is about 1.12 W/m·K, compared with FR-. 4 has a big forward. Due to its excellent heat dissipation, it has become the most widely used product in the market of high-power LED heat-dissipating substrates. However, it also has its inherent defects: the thermal conductivity of the polymer insulation layer is low, as long as 0.3 W/m·K, causing the heat not to pass directly from the chip to the metal base; the heat reduction of the metal Cu and Al Larger coefficients may constitute a more serious thermal mismatch problem.

The most representative material of the metal matrix composite substrate is aluminum silicon carbide. Aluminum SiC is a metal matrix composite that combines the low shortening factor of SiC ceramics with the high thermal conductivity of metal Al. It summarizes the advantages of both materials, with low density, low thermal shortening factor, 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



Ceramic substrate materials are mainly Al2O3, aluminum nitride, SiC, BN, BeO, Si3N4, etc. Compared with other substrate materials, ceramic substrates have the following properties in mechanical, electrical and thermal properties:
(1) Mechanical function. Mechanical strength, can be used as a support member; good processability, high dimensional accuracy; smooth appearance, no microcracks, tortuosity, etc.
(2) Thermal properties. The thermal conductivity is large, the thermal shortening coefficient is matched with chip materials such as Si and GaAs, and the heat resistance is good.
(3) Electrical properties. Low dielectric constant, low dielectric loss, insulation resistance and insulation damage, high stability, high reliability under high temperature and high humidity conditions.
(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.
Ceramic substrates For a long time, Al2O3 and BeO ceramics are two main substrate materials for high-power packaging. However, the two substrate materials are inherently defective. The thermal conductivity of Al2O3 is low, and the thermal shortening coefficient does not match the chip material. BeO has an excellent induction function, but the consumption cost is high and highly toxic. Therefore, from the perspective of function, cost and environmental protection, neither of these substrate materials can be used as the ideal material for future high-power LED devices. Aluminum nitride ceramics have excellent functions such as high thermal conductivity, high strength, high electrical resistivity, low density, low dielectric constant, non-toxicity, and thermal shortening coefficient matched with Si, and will gradually replace traditional high-power LED substrate materials. It is the ceramic substrate material that will be the most out of the future.
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