Most of the heat generated by the LED is transferred to the heat sink of the carrier board through the substrate, and then rapidly in a horizontal manner.
The heat is transferred to the entire carrier board at a high speed, and the heat is finally conducted vertically to the large area of the casing, which promotes heat convection and radiation on the surface of the casing. The hot air from the ventilation holes is used to flow upward or forced convection due to wind dissipation to cause heat movement to dissipate the heat. take away.
There are three main ways to reduce the heat accumulation of LEDs. One is to improve the characteristics of the die.
In the production stage, the energy configuration to increase the luminous efficiency and reduce the heat generation, in addition, the traditional wafers all use sapphire as the substrate, the thermal conductivity of sapphire is only about 20W/mK, and it is difficult to quickly discharge the heat generated by the epitaxial layer to the outside, so Cree The company replaces sapphire with "silicon" with high thermal conductivity to improve heat dissipation.
In addition, the larger the size of the die LED thermal resistance value is smaller.
The second is the Die Bonding method, which is changed from Wire Bonding to Flip-Chip. The traditional LED package uses the wire bonding method, but compared with metal, the heat transfer of sapphire is quite slow, so the heat source will be conducted from the metal wire, but the heat dissipation effect is not good. Invert the die on the heat dissipation substrate in a flip-chip manner, to exclude the sapphire from the heat conduction path, and increase the heat transfer area on the geometric structure to reduce the thermal resistance.
The third is that the packaging substrate adopts materials with high thermal conductivity such as aluminum oxide, aluminum nitride, beryllium oxide and boron nitride, which are matched with the thermal expansion coefficient of the LED, thereby reducing the total thermal resistance of the entire heat dissipation substrate.
In the early days, LEDs were packaged in a shell-type way. A small part of the heat source in the heat dissipation path dissipated heat to the atmosphere through the protective layer. Most of the heat sources could only dissipate heat to the substrate through the metal frame. The thermal resistance of this package was quite large, reaching 250-350C/ W. Furthermore, it is packaged on the PCB substrate by surface mounting (SMD), mainly through the FR4 carrier that is attached to the substrate to conduct heat, and the thermal resistance value is greatly reduced by increasing the heat dissipation area.
NINGBO MINGXING LIGHTING CO., LTD.is a work light manufacturer, producing floodlights with a tripod stand, and portable rechargeable led flood lights.