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Ceramic substrate is a potential material

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  At present,with the development of LED industry at home and abroad towards high efficiency,high density and high power,from 2017 to 2018,the overall domestic LED has developed rapidly,and the power is also increasing.The development of heat dissipation materials with excellent performance has become an urgent task to solve the problem of LED heat dissipation.Generally speaking,the luminous efficiency and service life of LED will decrease with the increase of temperature.When the temperature reaches above 125℃,the LED will even fail.In order to keep the junction temperature of LED at low temperature,it is necessary to use heat dissipation substrate materials with high thermal conductivity and low thermal resistance and reasonable packaging technology to reduce the thermal resistance of the whole LED packaging.

  At present,the commonly used substrate materials include Si,metal and metal alloy materials,ceramics and composite materials.The thermal expansion coefficient and thermal conductivity are shown in the table below.Because of the inherent conductivity and thermal expansion coefficient of metal and metal alloy materials with high cost of Si material,it is difficult to process ceramic materials which are inconsistent with chip materials,so it is difficult to meet the performance requirements of high-power substrate at the same time.

  Since the development of power LED packaging technology,the main heat dissipation substrates are epoxy resin covered copper substrate,metal covered copper substrate,metal composite substrate,ceramic covered copper substrate,etc.

  Epoxy resin coated copper substrate is the most widely used substrate in traditional electronic packaging.It plays a supporting,conductive and insulating role.Its main characteristics are low cost,high moisture resistance,low density,easy processing,easy realization of micro graphic circuit,suitable for large-scale production.However,the basic material of FR-4 is epoxy resin.The organic material has low thermal conductivity and poor high temperature resistance.Therefore,FR-4 can not meet the requirements of high-density and high-power LED,and is generally only used for low-power LED packaging.

  Metal based covered copper substrate is a new substrate after FR-4.Copper foil circuit and polymer insulation layer are directly bonded to metal and base with high thermal conductivity through thermal conductive bonding materials.The thermal conductivity is about 1.12w/mk,which is greatly improved than FR-4.Due to its good heat dissipation,it has become the most widely used product in the market of high-power LED heat dissipation substrate.However,the thermal conductivity of polymer insulation layer is low,only 0.3w/mk.The thermal expansion coefficient of Cu and Al,which can not be transferred directly from the chip to the metal base,may cause serious thermal mismatch.

Ceramic substrate

  The most representative material of metal matrix composite board is aluminum silicon carbide.Aluminum silicon carbide is a kind of metal matrix composite material which combines the low expansion coefficient of SiC ceramic and 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 coefficient of thermal expansion of adjacent materials,so as to minimize the thermal stress.

  The common ceramic substrates are Al2O3,AlN,SiC,BN,BeO,Si3N4,etc.compared with other substrates,ceramic substrates have mechanical,electrical and thermal properties

  (1)Mechanical properties.The mechanical strength can be used as a support component,with good processability,high dimensional accuracy,smooth surface,no microcrack,bending,etc.

  (2)Thermal properties.High thermal conductivity,thermal expansion coefficient and Si,GaAs and other chip materials match,good heat resistance.

  (3)Electrical properties.It has the advantages of low dielectric constant,low dielectric loss,high insulation resistance and insulation damage,stable performance and high reliability under high temperature and high humidity conditions.

  (4)Other properties.It has the advantages of good chemical stability,no moisture absorption,oil resistance,chemical resistance,non-toxic,pollution-free,small release ofα-ray,stable crystal structure,not easy to change within the range of operating temperature,and rich in raw material resources.

  For a long time,Al2O3 and BeO ceramics are two main substrate materials for high power packaging.However,these two substrate materials have disadvantages.BeO,which has low thermal conductivity and inconsistent thermal expansion coefficient with chip material,has excellent comprehensive performance,but it has high production cost and is highly toxic.Therefore,in terms of performance,cost and environmental protection,these two substrate materials can not be used as the most ideal materials for the development of high-power LED equipment in the future.AlN Ceramics have excellent properties such as high thermal conductivity,high strength and strength,high resistivity,low density,low dielectric constant,non-toxic,thermal expansion coefficient matching with Si.It has replaced the traditional high-power LED substrate materials and become the most promising ceramic substrate materials in the future.
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