At present, common types of substrates include hard printed circuit boards, high thermal conductivity aluminum substrates, ceramic substrates, flexible printed circuit boards, and metal composite materials. Generally, low-power LED packages can meet the needs of PCB boards used in the general electronics industry. However, LED packages of more than 0.5W are mostly replaced with metal-based and ceramic-based high-heat-dissipation substrates. The main reason is that the heat dissipation of the substrate is related to the lifetime of the LEDs. Performance has a direct impact, so the package substrate is a very important component in the design of high-brightness LED products.
In the process of converting electricity into light, nearly 80% of it becomes heat. With so much heat, it is impossible to completely export so much heat from two pins. We have to rely on heat sinks to dissipate heat. In fact, a lot of heat will not burn particles in such a small space, but it will make the light weaker and weaker, which is what we usually call light decay. Only when the heat is emitted quickly, the light decay is smaller.
Below, we discuss the application advantages in LED components from three aspects: heat dissipation, thermal expansion, and dimensional stability of metal package substrates:
1, heat dissipation
At present, many double-panel and multi-layer boards have high density, high power and difficult heat dissipation. Conventional printed board substrates such as FR4 and CEM3 are poor conductors of heat, which are insulated between layers and heat is not emitted. Local heating of electronic equipment is not ruled out, resulting in high temperature failure of electronic components, and metal-based printed boards can solve this heat dissipation problem.
2, thermal expansion
Thermal expansion and contraction are the common nature of matter. The coefficient of thermal expansion (CTE) is different. The printed board is a composite of resin + reinforcing material (such as glass fiber) + copper foil. In the XY axis direction of the board, the coefficient of thermal expansion (CTE) of the printed board is 13~18 PPM/°C, 80~90PPM/°C in the Z-axis direction, and the CTE of copper is 16.8PPM/°C. The CTE of the chip-shaped ceramic wafer carrier is 6 PPM/° C. The metallized hole wall of the printed board and the connected insulating wall have a large difference in the C-axis of the Z-axis, and the generated heat cannot be eliminated in time, and the thermal expansion and contraction causes the metallized hole to be cracked. And disconnected, so the machine equipment is not reliable.
SMT (Surface Mount Technology) makes this problem more prominent and becomes a problem that cannot be solved. Because the surface mount interconnect is achieved by direct connection of surface solder joints, the ceramic wafer carrier CTE is 6 and the FR4 substrate has a CTE of 13-18 in the XY direction. Therefore, the mount solder joints are different due to the CTE. Long-term stress can cause fatigue fracture.
The metal-based printed board can effectively solve the heat dissipation problem, thereby alleviating the thermal expansion and contraction of different materials on the printed board, and improving the durability and reliability of the whole machine and the electronic equipment.
3, dimensional stability
Metal-based printed boards are clearly much more dimensionally stable than printed boards of insulating materials. The aluminum-based printed board and the aluminum sandwich panel are heated from 30 ° C to 140 to 150 ° C, and the dimensional change is 2.5 to 3.0%. The metal-based circuit board has excellent thermal conductivity, good machinability and strength, good electromagnetic shielding performance, and good magnetic properties. The product design follows the semiconductor heat conduction mechanism, so not only the heat conductive metal circuit board (metal PCB): the aluminum substrate and the copper substrate have good heat conduction and heat dissipation. And green and environmentally friendly, both to solve the problem of heat and solve the problem of polluting the environment. (small soup)
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