Explain the status and development of ceramic substrates used in LED packaging

Explain the status and development of ceramic substrates used in LED packaging

2022-05-24 13:35:37 12

Direct copper-lined ceramic substrates are widely used because of the excellent electrical and thermal conductivity of copper and the high mechanical strength and low dielectric loss of ceramics. In the past decades, copper-lined substrates have made a great contribution to power electronics packaging, which is mainly attributed to the following performance characteristics of direct copper-lined substrates.


  Good thermal properties.

  Capacitive properties.

  High insulation properties.

  Si-matched coefficient of thermal expansion.

  Excellent electrical properties and high current carrying capacity.


  Direct copper-laying ceramic substrates were originally developed to address high currents and heat dissipation, and later applied to the metallization of AlN ceramics. In addition to the above features also have the following characteristics making it widely used in high power devices.


  Strong mechanical stress and stable shape; high strength, high thermal conductivity and high insulation; strong bonding and corrosion resistance.


  Excellent thermal cycling performance, with 50,000 cycles and high reliability.


  Structures that can be etched with various graphics as with PCBs (or IMS substrates); pollution-free and non-polluting.


  Wide use temperature -55℃~850℃; thermal expansion coefficient close to silicon, simplifying the production process of power modules.


  The coefficient of thermal expansion of DBC is close to that of silicon chip, which can save the transition layer Mo piece, save labor, save material and reduce cost. The line width is only 10% of that of an ordinary printed circuit board; its excellent thermal conductivity allows for a very compact package of chips, which results in a much higher power density and improved reliability of systems and devices.


  In order to improve the thermal conductivity of the substrate, generally is to reduce the thickness of the substrate, ultra-thin (0.25mm) DBC board can replace BeO, direct copper thickness can reach 0.65mm, so that the direct copper ceramic substrate can carry a larger current and temperature rise is not obvious, 100A current continuously through 1mm wide 0.3mm thick copper body, temperature rise of about 17 ℃; 100A current continuously Through 2mm wide 0.3mm thick copper body, the temperature rise is only about 5℃. Compared with brazing and Mo-Mn method, DBC has a very low thermal resistance characteristic, taking the thermal resistance of 10&TImes;10mm DBC plate as an example.


  The thermal resistance of 0.63mm thickness ceramic substrate DBC is 0.31K/W, 0.38mm thickness ceramic substrate DBC is 0.19K/W, and 0.25mm thickness ceramic substrate DBC is 0.14K/W.


  Alumina ceramics have the highest resistance and their insulation withstand voltage is also high, so as to guarantee personal safety and equipment protection capability; in addition to this DBC substrate can realize new packaging and assembly methods, so that the product is highly integrated and reduced in size.

 4.3.1 Development trend of direct copper ceramic substrate


  In high-power, high-density packaging, electronic components and chips in the operation of the heat generated mainly through the ceramic substrate to the environment, so the ceramic substrate in the process of heat dissipation plays an important role. AlN ceramics have high thermal conductivity, suitable for high-power semiconductor substrates, natural cooling in the cooling process can achieve the purpose, but also has good mechanical strength, excellent electrical properties. Although the current domestic manufacturing technology still needs to be improved, the price is also more expensive, but its annual production increase rate than Al2O3 ceramics more than 4 times higher than the future can replace BeO and some non-oxide ceramics. So the use of AlN ceramics to do insulating thermal substrate is the trend, but there is a time and cost problem.


  4.3.2 direct aluminum (DAB) ceramic substrate and direct copper ceramic substrate (DBC) performance comparison


  Directly laying aluminum substrate as an insulation carrier applied to electronic circuits and made great progress, the technology borrowed? This technology is based on the direct laying copper ceramic substrate technology. This new type of direct laying Al substrate has shown good properties in theory and experiment. Although its properties are similar to those of direct Cu substrates in many aspects. For direct laying Cu substrate, because the expansion coefficient of metallic copper is 17.0 ′10-6/°C at room temperature, 96 alumina ceramic substrate thermal expansion coefficient of 6.0′10-6/°C at room temperature, copper and alumina laying temperature is higher (more than 1000 ℃), the interface will form a relatively hard product CuAlO2, so the laying of copper alumina substrate internal stress, thermal shock resistance Performance is relatively poor, often damaged in use due to fatigue.


  Compared with copper, aluminum has a lower melting point, low price and good plasticity, the melting point of pure aluminum is only 660 ℃, the coefficient of expansion of pure aluminum at room temperature is 23.0′ 10-6/℃, the laying of metallic aluminum and alumina ceramic substrates is physical wetting, there is no chemical reaction at the interface, and the excellent plasticity of pure aluminum can effectively relieve the thermal stress caused by the difference in the coefficient of thermal expansion of the interface. Research has also confirmed that Al/Al2O3 ceramic substrates have very good thermal shock resistance. This is the direct laying Cu substrate can not be compared, while the metal aluminum and alumina ceramics between the peeling strength is also greater.


  Directly laying aluminum substrate as a substrate is particularly suitable for power electronic circuit directly laying aluminum substrate performance is different from the performance of directly laying copper substrate, the former has better stability performance under high temperature cycle. Directly laying aluminum substrate chip also shows better stability than directly laying copper substrate. With its high thermal shock resistance and low weight, the direct aluminum substrate is expected to develop better performance in the future to meet the higher demand.


  4.3.3 Trends of aluminized ceramic substrates


  Aluminum-lined ceramic substrates (DAB) are used in insulation carriers with their unique properties, especially for power electronic circuits. This new material is similar to direct copper substrate (DBC) in many aspects, and itself has significant thermal shock resistance and thermal stability performance, which is very obvious to improve the stability of devices working at extreme temperatures. DAB substrates have great potential for devices with special requirements for high reliability, which makes them ideal for optimizing power electronic systems, automation, aerospace, etc.


  4.4 DPC (Direct Plate Copper)


  DPC is also known as direct copper plating substrate, DPC substrate process for example: first of all, the ceramic substrate to do pre-treatment cleaning, the use of thin film manufacturing technology - vacuum coating on the ceramic substrate sputtering combined with copper-metal composite layer, followed by yellow light micro-shadow of the photoresist was re-exposure, development, etching, de-filming process to complete the line production, and finally by electroplating / chemical plating deposition method After the photoresist is removed, the metalized line is completed. The detailed DPC production flow chart is shown below.


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