LED power is also growing, the development of the superior performance of cooling materials has become a top priority to solve the problem of LED cooling. In general, the LED luminous efficiency and service life decline with the increase of the junction temperature, when the junction temperature reached 125 ? above, the LED can appear even failure. In order to keep LED junction temperature at a lower temperature, it is necessary to adopt heat dissipation substrate material with high thermal conductivity and low thermal resistance and reasonable packaging technology to reduce the overall packaging thermal resistance of LED. At present, common substrate materials include Si, metal, metal alloy materials, ceramics, and composite materials. Their thermal expansion coefficient and thermal conductivity are shown in the table below. Si material cost is high. The inherent conductivity and thermal expansion coefficient of metal and metal alloy materials do not match the chip materials. Ceramic materials are difficult to process and other shortcomings, it is hard to meet all requirements of high power substrate.
Epoxy resin coated copper substrate is the most widely used substrate in traditional electronic packaging. It supports, conducts electricity and insulates. Its main characteristics are low cost, high moisture absorption resistance, low density, easy processing, easy to achieve micro-graphics circuit, suitable for mass production. However, as the base material of fr-4 is epoxy resin, the organic material has low thermal conductivity and poor high-temperature resistance, so fr-4 cannot meet the requirements of high-density and high-power LED packaging and is generally only used in low-power LED packaging. Metal - clad copper substrate is a new type of substrate after FR-4. It is made by directly bonding copper foil circuit and polymer insulation layer with metal and base with high thermal conductivity through thermal conductivity bonding material, and its thermal conductivity is about 1.12w /m?K, which is greatly improved compared with fr-4. Due to its excellent heat dissipation, it has become the most widely used product in the market of high-power LED heat dissipation substrate. But it also has its inherent disadvantages: the thermal conductivity of the polymer insulation layer is low, only 0.3 W/m?K, resulting in the heat cannot be very good from the chip directly to the metal base; The thermal expansion coefficient of Cu and Al is large, which may cause serious thermal mismatch. The most representative material of metal matrix composite substrate is aluminum silicon carbide. Aluminum carbide is a metal matrix composite material that combines the low expansion coefficient of SiC ceramics with the high thermal conductivity of metal Al. It combines the advantages of the two materials and has a series of excellent characteristics such as low density, low thermal expansion coefficient, high thermal conductivity, and high stiffness. The thermal expansion coefficient of AlSiC can be adjusted by changing the content of SiC to match the thermal expansion coefficient of adjacent materials, thus minimizing the thermal stress of the two materials. Therefore, aluminum nitride ceramics have excellent properties such as high thermal conductivity, high strength, high resistivity, low density, low dielectric constant, non-toxic, and si-matched thermal expansion coefficient, etc., which will gradually replace the traditional high-power LED substrate material and become a kind of ceramic substrate material with the most promising future.
PCB prototype parameter
2 Layer, aluminum nitride ceramics, 1.6mm, Immersion Gold
L1: The copper of the second step:0.6mm?17 OZ?
The copper of the first step:0.4mm (11.5 OZ)
CCL 0.2MM aluminum nitride ceramics
L2: copper thickness:0.4mm(11.5 OZ)