PCB News - Comparison and analysis of ceramic PCB applied to power LED

Comparison and analysis of ceramic PCB applied to power LED
The power LED package PCB acts as a carrier of heat and air convection, and its thermal conductivity plays a decisive role in the heat dissipation of the LED. DPC ceramic PCB shows strong competitiveness among many electronic packaging materials due to its excellent performance and gradually reduced price, and it is the development trend of power LED packaging in the future. With the development of science and technology and the emergence of new preparation processes, high thermal conductivity ceramic materials as a new type of electronic packaging PCB material have a very broad application prospect.
With the continuous increase of the input power of LED chips, the large heat generated by the large power dissipation puts forward newer and higher requirements for LED packaging materials. In the LED heat dissipation channel, the package PCB is the key link to connect the internal and external heat dissipation channels, and it has the functions of heat dissipation channel, circuit connection and physical support for the chip. For high-power LED products, the package PCB requires high electrical insulation, high thermal conductivity, and thermal expansion coefficient matching the chip.

Resin-based encapsulation PCB: high supporting cost is still difficult to popularize

Emc and SMC have high requirements for compression molding equipment, and the price of a compression molding production line is about 10 million yuan, which is still difficult to popularize on a large scale.
The SMD LED brackets that have emerged in recent years generally use high-temperature modified engineering plastic materials, using PPA (polyphthalamide) resin as raw materials, and adding modified fillers to enhance certain physical and chemical properties of PPA raw materials. This makes the PPA material more suitable for injection molding and the use of SMD LED stents. The thermal conductivity of PPA plastic is very low, and its heat dissipation is mainly carried out through the metal lead frame, and the heat dissipation capacity is limited, which is only suitable for low-power LED packaging.

Metal core printed circuit board: complex manufacturing process and fewer practical applications
The processing and manufacturing process of aluminum-based PCB is complicated and costly, and the thermal expansion coefficient of aluminum is quite different from the chip material, so it is rarely used in practical applications. Most high-power LED packages use this kind of PCB, and the price is between medium and high prices.
The current production of general high-power LED heat dissipation PCBs has extremely low thermal conductivity of the insulating layer, and the existence of the insulating layer makes it unable to withstand high-temperature soldering, which limits the optimization of the package structure and is not conducive to the heat dissipation of the LED.

Silicon-based packaging PCB: Facing challenges, the yield rate is less than 60%
Silicon-based PCBs face challenges in the preparation of insulating layers, metal layers, and vias, and the yield rate does not exceed 60%. Silicon-based materials are used as LED packaging PCB technology and have been applied in the LED industry in the semiconductor industry. The thermal conductivity and thermal expansion properties of silicon-based PCBs indicate that silicon is a better packaging material for LEDs. The thermal conductivity of silicon is 140W/m·K. When applied to LED packaging, the resulting thermal resistance is only 0.66K/W; and silicon-based materials have been widely used in semiconductor manufacturing processes and related packaging fields, involving related equipment and materials Has been quite mature. Therefore, if silicon is made into LED package PCB, mass production is easy.
However, LED silicon PCB packaging still has many technical problems. For example, in terms of materials, silicon is easily broken, and the strength of the mechanism is also problematic. In terms of structure, although silicon is an excellent heat conductor, it has poor insulation and must be oxidized and insulated. In addition, the metal layer needs to be prepared by sputtering combined with electroplating, and the conductive holes need to be made by corrosion. In general, the preparation of insulating layers, metal layers, and vias are all facing challenges, and the yield rate is not high.

Ceramic package PCB: improve heat dissipation efficiency to meet the needs of high-power LEDs
The ceramic substrate with high thermal conductivity significantly improves the heat dissipation efficiency and is the most suitable product for the development needs of high-power, small-size LEDs. Ceramic PCB has a new thermal conductive material and a new internal structure, which makes up for the defects of aluminum metal PCB, thereby improving the overall heat dissipation effect of the PCB. Among the ceramic materials currently used for heat dissipation PCBs, BeO has high thermal conductivity, but its linear expansion coefficient is very different from that of silicon, and it is toxic during manufacture, which limits its own application; BN has good overall performance, but it is used as a PCB The material has no outstanding advantages and is expensive. It is only under research and promotion at present; silicon carbide has high strength and high thermal conductivity, but its resistance and insulation withstand voltage are low, and the bonding is unstable after metalization, which will cause The change of thermal conductivity and dielectric constant is not suitable as an insulating packaging PCB material. Although Al2O3 ceramic substrate is currently the most widely produced and most widely used ceramic substrate, its thermal expansion coefficient is higher than that of Si single crystal, which makes Al2O3 ceramic substrate not suitable for high-frequency, high-power, and very large-scale integrated circuits. Used in. A1N crystal has high thermal conductivity and is considered to be an ideal material for a new generation of semiconductor PCB and packaging.

AlN ceramic PCB has been widely studied since the 1990s and gradually developed. It is currently generally considered to be a promising electronic ceramic packaging material. The heat dissipation efficiency of AlN ceramic PCB is 7 times that of Al2O3. The heat dissipation efficiency of AlN ceramic PCB applied to high-power LEDs is significant, which greatly increases the service life of LEDs.
The direct copper clad ceramic board (DBC) developed based on on-board packaging technology is also a ceramic PCB with excellent thermal conductivity. DBC does not use a bonding agent in the preparation process, so it has good thermal conductivity, high strength, strong insulation, and the thermal expansion coefficient matches with semiconductor materials such as Si. However, ceramic PCBs have low reactivity with metal materials, poor wettability, and it is difficult to implement metallization. It is difficult to solve the problem of micro-pores between Al2O3 and copper plates, which makes the mass production and yield of this product more challenging., Is still the focus of research by domestic and foreign researchers. At present, only a few companies led by Stone Group are capable of mass production in China.
DPC ceramic PCB is also known as direct copper-plated ceramic board. DPC products have the characteristics of high circuit accuracy and high surface flatness. They are very suitable for LED flip chip/eutectic technology. With a high thermal conductivity ceramic substrate, the heat dissipation efficiency is significantly improved. It is a cross-age product most suitable for the development needs of high-power, small-size LEDs.