Power LED package PCB serves as a carrier of heat and air convection, and its thermal conductivity plays a decisive role in the heat dissipation of LEDs. DPC ceramic PCB, with its excellent performance and gradually decreasing price, has shown strong competitiveness among many electronic packaging materials and 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 have broad application prospects as new electronic packaging PCB materials.
As the input power of LED chips continues to increase, the large heat generated by large dissipation power has put forward newer and higher requirements for LED packaging materials. In the LED heat dissipation channel, the packaging PCB is the key link connecting the internal and external heat dissipation channels, and has the functions of heat dissipation channel, circuit connection and physical support for the chip. For high-power LED products, the packaging PCB requires high electrical insulation and high conductivity. Characteristics such as thermal properties and thermal expansion coefficient matching the chip.
Resin-based packaging PCB: high supporting costs and difficulty in popularization
EMC and SMC have high requirements for molding equipment. The price of a molding production line is about 10 million yuan, so large-scale popularization is still difficult.
The SMD LED brackets that have emerged in recent years generally use high-temperature modified engineering plastics, using PPA (polyphthalamide) resin as the raw material. Some physical and chemical properties of the PPA raw materials are enhanced by adding modified fillers, making the PPA material more suitable for injection molding and the use of SMD LED brackets. The thermal conductivity of PPA plastic is very low, and its heat dissipation is mainly carried out through the metal lead frame. The heat dissipation capacity is limited, and it is only suitable for low-power LED packaging.
Metal core printed circuit board: The manufacturing process is complex and few practical applications
The processing and manufacturing process of aluminum-based PCB is complex and costly. The thermal expansion coefficient of aluminum is quite different from that of chip materials, so it is rarely used in practical applications. High-power LED packages mostly use this type of PCB, and their prices range between mid- and high-price ranges.
The thermal conductivity of the insulation layer of the high-power LED heat dissipation PCB commonly used in production is extremely low, and due to the existence of the insulation layer, it cannot withstand high-temperature welding, which limits the optimization of the packaging structure and is not conducive to LED heat dissipation.
Silicon-based package PCB: Facing challenges, the yield rate is less than 60%
Silicon-based PCB faces challenges in the preparation of insulation layers, metal layers, and via holes, and the yield rate does not exceed 60%. Using silicon-based materials as LED packaging PCB technology has been applied in the LED industry in the semiconductor industry. The thermal conductivity and thermal expansion properties of silicon-based PCB indicate that silicon is a packaging material that is more suitable for LEDs. The thermal conductivity of silicon is 140W/m·K. When used in LED packaging, the resulting thermal resistance is only 0.66K/W. Moreover, silicon-based materials have been widely used in semiconductor manufacturing processes and related packaging fields, and the related equipment and materials involved are quite mature. Therefore, if silicon is made into LED packaging PCB, mass production can be easily achieved.
However, there are still many technical problems with LED silicon PCB packaging. For example, in terms of materials, silicon is prone to fragmentation and has issues with its structural strength. In terms of structure, although silicon is an excellent thermal conductor, it has poor insulation and must be oxidized and insulated. In addition, the metal layer needs to be prepared by sputtering and electroplating, and the conductive holes need to be etched. Overall, the preparation of insulating layers, metal layers, and via holes all face challenges, and the yield rate is not high.
Ceramic package PCB: improves heat dissipation efficiency to meet the needs of high-power LEDs
With a high thermal conductivity ceramic substrate, the heat dissipation efficiency is significantly improved, making it the most suitable product for the development needs of high-power, small-size LEDs. Ceramic PCB has new thermal conductive materials and new internal structure, which makes up for the defects of aluminum metal PCB, thereby improving the performance of PCB. Overall cooling effect. Among the ceramic materials that can currently be used as heat dissipation PCBs, although BeO has a high thermal conductivity, its linear expansion coefficient is very different from silicon, and it is toxic during manufacturing, which limits its application; BN has good overall performance, but as a PCB material, it has no outstanding advantages. It is also expensive and is currently only under research and promotion. Silicon carbide has high strength and high thermal conductivity, but its resistance and insulation withstand voltage are low. The bonding after metallization is unstable, which will cause changes in thermal conductivity and dielectric constant. It is not suitable as an insulating packaging PCB material. Although Al2O3 ceramic substrate is currently the most produced and widely used ceramic substrate, due to its higher thermal expansion coefficient compared to Si single crystal, Al2O3 ceramic substrate is not suitable for use in high-frequency, high-power, and ultra-large-scale integrated circuits. A1N crystal has high thermal conductivity and is considered an ideal material for new generation semiconductor PCBs and packaging.
AlN ceramic PCB has been extensively studied and gradually developed since the 1990s. It is currently generally believed to be very Electronic ceramic packaging materials with promising development prospects. The heat dissipation efficiency of AlN ceramic PCB is 7 times that of Al2O3. The heat dissipation efficiency of AlN ceramic PCB when used in high-power LEDs is significant, thereby greatly extending 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 binder during the preparation process, so it has good thermal conductivity, high strength, strong insulation, and a thermal expansion coefficient that matches that of semiconductor materials such as Si. However, ceramic PCB has low reactivity with metal materials and poor wettability. It is quite difficult to implement metallization and it is not easy to solve the problem of micropores between Al2O3 and copper plates. This makes the mass production and yield rate of this product a greater challenge. It is still the focus of research by domestic and foreign researchers. At present, only a few companies in China, led by Siton, are capable of mass production.
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 processes. With the high thermal conductivity ceramic substrate, the heat dissipation efficiency is significantly improved. It is a cross-generation product that is most suitable for the development needs of high-power, small-size LEDs.
ANNA