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What is the research of aluminum nitride ceramic substrate in IGBT module

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  In the fields of electric vehicles,electric locomotives,smart grids,etc.,insulated gate bipolar transistors(IGBTs)are required to implement power conversion and control as power electronic devices.Aluminum nitride ceramic copper-clad board not only has the characteristics of high thermal conductivity,high electrical insulation,high mechanical strength,low expansion of ceramics,but also the high conductivity of oxygen-free copper and excellent soldering performance.It is the key foundation of IGBT module packaging.material.In this paper,direct copper-cladding(DBC)and active metal welding(AMB)processes are used to prepare aluminum nitride ceramic copper-clad laminates.The similarities and differences between the two processes and the performance differences of the prepared aluminum nitride ceramic copper-clad laminates are compared.Silicon-ceramic copper-clad laminates are expected to be widely used in next-generation power modules.
  IGBT ceramic substrate
  Background of IGBT as power electrical power device
  With the intensive introduction of a series of policies such as"Made in China 2015","Implementation Plan for Industrial Green Development Special Actions","Guiding Opinions on Accelerating the Promotion and Application of New Energy Vehicles"and"UHV Planning",China's high-speed railways,cities Rail transit,new energy vehicles,smart grids,and wind power projects have become hot spots for the"green economy"in the coming years.These projects have an urgent and huge demand for high-voltage and high-power IGBT modules.Due to the high technical threshold of high-voltage and high-power IGBT modules,it is more difficult.In particular,it is required to have better heat dissipation performance,higher reliability and larger current carrying capacity of packaging materials.However,the backwardness of related domestic technologies has led the domestic high-voltage IGBT market to be monopolized by countries in Europe,the United States,and Japan.High-voltage IGBT products have high prices,long delivery cycles,and insufficient production capacity,which have severely limited China's power locomotive,electric vehicles and new energy fields development of.
  IGBT(Insulated Gate Bipolar Transistor)stands for Insulated Gate Bipolar Transistor.It is the most advanced power electronic device for power conversion and control.It has large input impedance,small driving power,fast switching speed,high operating frequency,low saturation voltage,The safe working area is large and can withstand a series of advantages such as high voltage and high current.It is known as the"CPU"of modern industrial converters.It is widely used in strategic industries such as rail transit,aerospace,new energy vehicles,wind power generation,and defense industry.application.
  First,heat dissipation and principle of aluminum nitride ceramic copper-clad substrate
  The heat generated by the high-voltage and high-power IGBT module is mainly transmitted to the case through the ceramic copper-clad board,so the ceramic copper-clad board is an indispensable key basic material for power module packaging in the power electronics field.It not only has the characteristics of high thermal conductivity,high electrical insulation,high mechanical strength,low expansion,etc.of ceramics,but also the high conductivity and excellent soldering performance of oxygen-free copper metal,and it can etch all kinds of PCBs like PCB circuit boards.Kind of graphics.Ceramic copper clad board combines various advantages of power electronic packaging materials:
  1)The ceramic part has excellent thermal and pressure resistance characteristics;
  2)The copper conductor part has extremely high current carrying capacity;
  3)High adhesion strength and reliability between metal and ceramics;
  4)Easy to etch patterns to form circuit substrates;

  5)Excellent welding performance,suitable for aluminum wire bonding.

ceramic substrate

  Aluminum nitride copper clad board has very high thermal conductivity in terms of thermal characteristics and fast heat dissipation;in terms of stress,the coefficient of thermal expansion is close to that of silicon,and the internal stress of the entire module is low,which improves the reliability of the high-voltage IGBT module.These excellent properties make aluminum nitride copper clad board the first choice for high voltage IGBT module packaging.In this paper,the methods of preparing aluminum nitride ceramic copper clad laminates by direct copper cladding process(DBC)and active metal welding process(AMB)are studied.The differences and similarities between the two processes and the performance differences of the aluminum nitride ceramic copper clad laminates prepared are compared.
  Ii.Preparation of aluminum nitride ceramic copper-clad board by direct copper-cladding process(DBC)
  The so-called DBC technology refers to directly heating a layer of copper foil on the surface of alumina or aluminum nitride ceramics by heating in an oxygen-containing nitrogen at a high temperature of about 1063°C.The basic principle is:the copper-oxygen eutectic liquid phase formed by copper and oxygen during sintering is used to wet the two material surfaces that are in contact with each other,that is,the surface of the copper foil and the surface of the ceramic,and also react with alumina to form CuAlO2,Cu(AlO2)2 and other composite oxides serve as eutectic brazing solders to achieve a strong bond between copper foil and ceramics[].However,since aluminum nitride is a non-oxide ceramic,the key to applying copper foil is to form an oxide transition layer on its surface,and then to laminate AlN and Cu foil by laminating the transition layer and Cu foil.
  Based on the above-mentioned basic theory,we systematically studied the aluminum oxide ceramic surface oxidation,oxygen-free copper oxidation,and direct copper cladding processes,optimized the process parameters,and prepared aluminum nitride ceramic copper cladding plates.No obvious voids were found in the sample,especially in the core area,and the void content in the upper and lower interfaces was less than 3%.The sample was cut into a 10 mm wide preformed cut,and the tensile force of copper pulled from the ceramic surface was tested.The peel strength of the sample was greater than 60 N/cm.
  The interface between ceramics and copper is tight and the structure is dense.Ceramic grains are about 1-5μm,and there is a 8-10 micron transition layer between copper and copper.The transition layer has a dense structure with about 3-5μm grains,but there are incoherent micro-cracks between the grains.The ceramic surface is dense with no pores.The surface particles are uneven,which may be caused by cracks extending along the grain boundaries when pulled apart,and some particles on copper and some particles on ceramics.
  III.Preparation of Aluminum Nitride Ceramic Copper Clad Substrate by Active Metal Welding Process(AMB)
  The active soldering copper process is a further development of DBC process technology.It is a method of using a small amount of active elements contained in solder to react with ceramics to form a reaction layer that can be wetted by liquid solder,thereby achieving ceramic-metal bonding.Active ceramic solder is printed on the ceramic surface,then it is clamped with oxygen-free copper and then soldered at high temperature in a vacuum brazing furnace.After the bonding,the substrate is fabricated on the surface using a wet etching process similar to that of a PCB.To produce reliable products.The AMB substrate is bonded by the chemical reaction between ceramic and active metal solder paste at high temperature,so its bonding strength is higher and its reliability is better.However,due to the higher cost of this method,less suitable solder,and the greater impact of solder on solder reliability,only a few Japanese companies have mastered highly reliable active metal soldering technology.
  Through the optimization of different solder formulations,we have developed a special active solder paste system for aluminum nitride ceramics that is suitable for active welding of aluminum nitride ceramics.The solder paste has a simple preparation process,excellent printing characteristics,and wettability with aluminum nitride ceramics.Good and high bonding strength after welding.
  Adopt solder paste screen printing technology and vacuum welding technology to achieve good welding of aluminum nitride and copper.Through research and optimization of welding methods,achieve good control of aluminum nitride and copper welding strength and welding interface,interface void ratio Less than 1%,and solidified the welding process curve.
  AMB substrate requires better weldability of the plating layer during pressure welding,and has good adhesion at 250°C,so its surface needs to be nickel-plated.After the AMB substrate is etched with a pattern,there are a large number of islands on the surface.It is difficult to perform electroplating and the thickness of the coating is uneven.Therefore,electroless nickel plating is undoubtedly the best choice.In order to improve the uniformity of the nickel plating layer,electroless Ni-P technology is used to achieve nickel plating on the surface of the aluminum nitride ceramic copper-clad substrate.Through optimization of the plating solution and plating parameters,the thickness of the nickel layer can be controlled at 3-5μm,Uniformity can be controlled within±0.2μm.At the same time,the process experiments on the bondability of the aluminum nitride copper-clad board have a bonding thrust of more than 1700g,which meets the application reliability requirements of high-voltage IGBT modules.
  的The reliability of batch temperature impact of aluminum nitride copper-clad substrates is a key factor in its performance.It is required that after the chip soldering is completed,the aluminum nitride copper-clad substrates can withstand 100 times temperature cycles of-40°C to+150°C.We carried out a series of optimizations on the aluminum nitride ceramic copper-clad substrate,including the design optimization of the copper-clad substrate and the process optimization of the copper-clad substrate,and finally reached the temperature cycle reliability requirements.
  Through process research,our company independently developed two types of aluminum nitride ceramic copper-clad substrates.It can be concluded that the AMB process has higher reliability and better comprehensive performance than the DBC process,and the nitride produced by our company The aluminum-clad copper substrate has been comparable to the technical indicators of related products produced by Japanese companies.
  24.Development direction of ceramic copper-clad substrates for high-voltage IGBT modules
  The emergence of third-generation semiconductor materials represented by silicon carbide and gallium nitride has provided the possibility for further significant improvements in device performance.In order to meet the high-frequency,high-temperature,high-power application requirements of SiC-based/GaN-based three-generation semiconductor devices,in order to achieve high-density three-dimensional modular packaging of high-power power electronic devices,it is necessary to develop higher reliability,better temperature resistance,and current carrying capacity.Stronger ceramic copper-clad substrate.Silicon nitride ceramics have a lower bending strength of 2.4 times that of aluminum oxide and aluminum nitride,so they have much higher reliability than aluminum nitride and aluminum oxide.In particular,high strength can achieve the coating with thick copper substrates.Connection,greatly improving the thermal performance of the substrate.Compared with aluminum nitride and aluminum oxide,silicon nitride ceramic copper-clad board has obvious advantages in terms of current carrying capacity,heat dissipation capacity,mechanical properties,and reliability.At the same time,β-Si3N4 ceramics have a potentially high thermal conductivity(200~320W/m·K),but its microstructure is more complicated and the scattering of phonons is larger,so the thermal conductivity is lower[],which limits Its application as a power module substrate material.Therefore,more research is currently focused on how to improve the thermal conductivity of silicon nitride ceramics.High thermal conductivity ceramics should have the following conditions:(1)the average atomic weight is small;(2)the atom bonding strength is high;(3)the crystal structure is relatively simple;(4)the lattice anharmonic vibration is low.Methods to improve the thermal conductivity of silicon nitride ceramics include:(1)introduction ofβ-Si3N4 phase seeds;(2)selection of sintering aids;(3)molding process and heat treatment process.Therefore,in the field of high-power IGBT modules,silicon nitride ceramic copper-clad boards are widely used in future high-reliability power modules for electric vehicles because they can weld thicker oxygen-free copper and higher reliability.According to the material and process characteristics,the technical development direction of ceramic copper clad laminates is demonstrated.Aluminum nitride ceramic copper clad laminates are the main development direction in the field of high power power modules,and silicon nitride ceramic copper clad laminates are the main development direction in the high reliability power module field.
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