The heat dissipation problem is a key problem that must be solved in high-power LED packaging. Since the heat dissipation effect directly affects the life and luminous efficiency of LED products, effectively solving the heat dissipation problem of high-power LED packages plays an important role in improving the reliability and life of LED packages.
The packaging structure is divided into two types: micro spray structure and flip chip structure.
1. Micro spray structure
In this sealed system, the fluid in the fluid cavity forms a strong jet at the micro-nozzle under a certain pressure. This jet directly impacts the surface of the LED chip substrate and takes away the heat generated by the LED chip. Under the action of the micro-pump, the heated fluid enters the small fluid cavity and releases heat to the external environment, causing its own temperature to drop, and then flows into the micro-pump again to start a new cycle.
Advantages: The micro-jet structure has high heat dissipation performance and uniform temperature distribution on the LED chip substrate.
Disadvantages: The reliability and stability of the micropump have a great impact on the system, and the system structure is relatively complex, which increases the operating cost.
2. Flip chip structure
For traditional formal chips, the electrodes are located on the light-emitting surface of the chip, which will block part of the light and reduce the luminous efficiency of the chip.
Disadvantages: The heat generated by the PN of this structure is directed out through the sapphire substrate. Sapphire has a low thermal conductivity and a long heat transfer path. Therefore, the chip with this structure has a large thermal resistance and the heat is not easily dissipated.
The second major factor: packaging materials
LED packaging materials are divided into two types: thermal interface materials and substrate materials.
1. Thermal interface materials
Currently, commonly used thermal interface materials for LED packaging include thermally conductive glue and conductive silver glue.
(a) Thermal conductive adhesive
The main component of commonly used thermal adhesive is epoxy resin, so its thermal conductivity is small, thermal conductivity is poor, and thermal resistance is large.
Advantages: Thermal conductive adhesive has the characteristics of insulation, heat conduction, shock resistance, easy installation, and simple process.
Disadvantages: Due to the low thermal conductivity, it can only be used in LED packaging devices that do not have high heat dissipation requirements.
(b) Conductive silver glue
Conductive silver glue is a GeAs, SiC conductive substrate LED with a back electrode. It is a key packaging material in the dispensing or glue preparation process of red, yellow, and yellow-green chip LED packaging.
Advantages: It has the functions of fixing the bonding chip, electrical and thermal conductivity, and heat transfer, and has an important impact on the heat dissipation, light reflectivity, and VF characteristics of the LED device. As a thermal interface material, conductive silver glue is currently widely used in the LED industry.
2. Substrate material
A certain heat dissipation path of LED package devices is from the LED chip to the bonding layer to the internal heat sink to the heat dissipation substrate and finally to the external environment. It can be seen that the heat dissipation substrate is important for LED package heat dissipation. Therefore, the heat dissipation substrate must have the following characteristics: high thermal conductivity, insulation, stability, flatness and high strength.
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