Aluminum nitride ceramic substrate

Generally speaking, the luminous efficiency and service life of light-emitting diodes will decrease as the junction temperature increases. When the junction temperature reaches 125, the light-emitting diode may even fail. In order to keep the junction temperature of the light-emitting diode at a low temperature, it is necessary to adopt a high thermal conductivity and low thermal resistance aluminum nitride ceramic substrate material and a reasonable packaging process to reduce the overall package thermal resistance of the light-emitting diode.

Currently, commonly used substrate materials include silicon, metal and metal alloy materials, ceramics and composite materials. Their thermal expansion coefficient and thermal conductivity are shown in the table below. Among them, the cost of silicon materials 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, which are difficult to meet the various performance requirements of high-power substrates at the same time.

With the development of power LED packaging technology, heat dissipation substrates mainly include epoxy copper clad laminates, metal-based copper clad laminates, metal-based composite substrates, and ceramic copper clad laminates.

Epoxy resin copper clad substrate is the most widely used substrate in traditional electronic packaging. It serves three functions: support, conduction and insulation. Its main features are: low cost, high hygroscopicity, low density, easy processing, easy to realize fine graphic circuits, suitable for mass production, etc. However, since the base material of FR-4 is epoxy resin, the organic material has low thermal conductivity and poor high temperature resistance, so it cannot meet the requirements of high-density, high-power LED packaging. Generally, FR-4 is only used for low-power LED packages.

Metal-based copper clad substrate is a new type of substrate after FR-4. It is made by directly bonding copper foil circuit and polymer insulating layer with a metal with high thermal conductivity and a substrate through a thermally conductive bonding material. Its thermal conductivity is about 1.12 W/Mg, which is much higher than FR-4. Due to its excellent heat dissipation performance, it has become the most widely used product in the current high-power LED heat dissipation substrate market. However, it also has its inherent shortcomings: the thermal conductivity of the polymer insulating layer is low, only 0.3w/m.k, which results in the heat cannot be directly transferred from the chip to the metal substrate. Metallic copper and aluminum have large thermal expansion coefficients, which may cause serious thermal mismatch problems.