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What materials are made of ceramic substrates?

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  Ceramic substrate materials are widely used in power electronics,electronic packaging,hybrid microelectronics and multi-chip modules due to their excellent thermal conductivity and air tightness.This article briefly introduces the current status and future development of ceramic substrates.

  (1)Plastic materials VS ceramic materials.

  Plastics,especially epoxy resins,still occupy a dominant position in the entire electronic market due to their good economics.However,many special fields such as high temperature,linear expansion coefficient mismatch,air tightness,stability,mechanical properties,etc.are obviously not Yes,even if a large amount of organic bromide is added to the epoxy resin,it will not help.

  Plastics,especially epoxy resins,still occupy a dominant position in the entire electronic market due to their good economics.However,many special fields such as high temperature,linear expansion coefficient mismatch,air tightness,stability,mechanical properties,etc.are obviously not Yes,even if a large amount of organic bromide is added to the epoxy resin,it will not help.

  (2)The main categories of ceramic substrate materials.

  1,Al2O3.

  So far,alumina substrate is a commonly used substrate material in the electronics industry,because compared with most other oxide ceramics in terms of mechanical,thermal and electrical properties,it has higher strength and chemical stability,and has a rich source of raw materials,Suitable for various technology manufacturing and different shapes.

  2,BeO.

  The thermal conductivity is higher than that of aluminum,so it is used where high thermal conductivity is required.But when the temperature exceeds 300°C,it drops quickly.The important thing is that its toxicity limits its development.


ceramic substrate


  3,aluminum nitride.

  Aluminum nitride has two important properties worth noting:one is high thermal conductivity,and the other is the expansion coefficient matching silicon.The disadvantage is that even if there is a thin oxide layer on the surface,it will affect the thermal conductivity.Only by strictly controlling the materials and processes,can the aluminum nitride substrate with good consistency be manufactured.At present,my country's large-scale aluminum nitride production technology is not yet mature.The price of AlN is much higher than that of Al2O3,which is also a bottleneck restricting its development.Based on the above reasons,it can be known that alumina ceramics is still in a leading position in the fields of microelectronics,power electronics,hybrid microelectronics,power modules,etc.due to its superior comprehensive performance.

  (3)Manufacturing of ceramic substrates.

  It is difficult to manufacture high-purity ceramic substrates.Most ceramics have high melting points and high hardness,which limits the possibilities of ceramic processing.Therefore,glass with a lower melting point is often doped into ceramic substrates for fluxing or bonding,making the product easier to process.The preparation processes of Al2O3,BeO and AlN substrates are similar.The substrate is ground into a powder with a diameter of about a few microns and mixed with different glass fluxes and binders(including magnesium oxide and calcium oxide in the powder).In addition,some organic binders and different plasticizers are added to the mixture,and then ball milled to prevent agglomeration and make the components uniform,forming green ceramic sheets,and sintering at high temperature.Currently,ceramic molding mainly has the following methods:

  1.Rolling:spray the slurry on a flat surface and partially dry it to form a viscous sheet like putty,and then send the sheet to a pair of parallel large rollers for rolling to obtain a green ceramic sheet with uniform thickness.

  2.Casting:The slurry is coated with a sharp blade to form flakes on a moving conveyor belt.Compared with other processes,this is a low pressure process.

  3.Powder pressing:The powder is sintered in a hard cavity under high pressure(about 138 MPa).Although uneven pressure may cause excessive warpage,the sintered parts produced by this process are dense and have tight tolerances.

  4.Isostatic powder compaction:This process uses a mold surrounded by water or glycerin,and uses a pressure of up to 69MPa,which is more uniform and the parts made with less warpage.

  5.Extrusion:The slurry is extruded through a die.The slurry used in this process has low viscosity and it is difficult to obtain small tolerances.However,this process is economical and can obtain thinner parts than other methods.

  (4)Comparison of substrate types and their characteristics.

  There are currently four common ceramic heat sink substrates:HTCC,LTCC,DBC and DPC,among which HTCC is an earlier developed technology.However,due to the high sintering temperature,the selection of electrode materials is limited,and the manufacturing cost is relatively expensive,which promotes the development of LTCC.Although LTCC reduces the co-firing temperature to about 850°C,its disadvantage is that it is difficult to control the dimensional accuracy and product strength.

  However,DBC and DPC are specialized technologies that have been developed in China in recent years and can be mass-produced.DBC combines Al2O3 and copper plate through high temperature heating.Its technical bottleneck is that it is difficult to solve the problem of micropores between Al2O3 and copper plate,which makes the mass production energy and yield of products greatly challenged.DPC technology uses direct copper plating technology to deposit Cu on Al2O3 substrates.The process combines materials and thin film technology.The product is a ceramic heat dissipation substrate commonly used in recent years,but the material control and process technology integration capabilities are high,which makes it enter the DPC industry and stable The technical threshold for production is relatively high.
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