Ceramic PCB fabrication

What is ceramic PCB?

Ceramic PCB/ Ceramic substrate is a special process board that copper foil is directly bonded to the surface of alumina (Al2O3) or aluminum nitride (AlN) ceramic substrate (single or double sided) at high temperature. The ultra-thin composite substrate has excellent electrical insulation performance, high thermal conductivity, excellent solderability and high adhesion strength.  It can etch various patterns like PCB, and has great current carrying capacity. Therefore, ceramic substrate has become the basic material of high power electronic circuit structure technology and interconnection technology.

Classification of ceramic PCB

1. Classification by ceramic material

Al2O3

Alumina substrate is the most commonly used substrate material in the electronic industry, because in terms of mechanical, thermal and electrical properties, compared with most other oxide ceramics, its strength and chemical stability are high, and the source of raw materials is rich, which is suitable for various technical manufacturing and different shapes.

BeO

It has higher thermal conductivity than aluminum, so it can be used in occasions where high thermal conductivity is needed.  However, when the temperature exceeds 300 ℃, it decreases rapidly.  The most important reason is that its toxicity limits its development.

AlN

AlN has two very important properties to note: one is high thermal conductivity, the other is the expansion coefficient matching with Si. The disadvantage is that even if there is a very thin oxide layer on the surface, the thermal conductivity will be affected.  Only by strictly controlling the material and process, can the AlN substrate with good consistency be produced. However, with the improvement of economy and technology, this bottleneck will eventually disappear.

From the above reasons, we can know that alumina ceramics(Al2O3) are still in a leading position in microelectronics, power electronics, Hybrid Microelectronics, power modules and other fields due to its superior comprehensive properties. 

Comparison of aluminum nitride (AlN) and aluminum oxide(Al2O3) characteristics


2. According to manufacturing process

At present, there are five kinds of ceramic heat dissipation substrates: HTCC, LTCC, DBC, DPC and Lam.  HTCC / LTCC belongs to sintering process, and the cost will be higher.

HTCC (High-Temperature Co-fired Ceramic)

HTCC is also known as high temperature co fired multilayer ceramics.  The manufacturing process of HTCC is very similar to that of LTCC.  The main difference is that the ceramic powder of HTCC is not made of glass.  Therefore, HTCC must be dried and hardened to form embryo at 1300 ~ 1600 ℃, and then the through holes are drilled, and the holes and printed circuits are filled with screen printing technology. The main materials are tungsten, molybdenum and manganese with high melting point but poor ,conductivityFinally, it is sintered in layers.


LTCC (Low-Temperature Co-fired Ceramic)

LTCC-It is also called low temperature co fired multilayer ceramic substrate.  In this technology, inorganic aluminum oxide powder and about 30% ~ 50% glass material are added with organic binder to make it evenly mixed into mud like slurry.  Then, the slurry is scraped into flakes by a scraper, and then the flake slurry is formed into thin pieces by a drying process.  Then, through holes are drilled according to the design of each layer as the signal of each layer. The inner circuit of LTCC uses screen printing technology to fill holes and print lines on the green embryo respectively.  The inner and outer electrodes can use silver, copper, gold and other metals respectively.  Finally, each layer is stacked and placed in a sintering furnace at 850 ~ 900 ℃ for sintering and molding.


DBC (Direct Bonded Copper)

Direct copper deposition technology is to use the oxygen-containing eutectic liquid of copper to directly coat copper on ceramics.  Its basic principle is to introduce appropriate amount of oxygen between copper and ceramics before or during the bonding process.  In the range of 1065 ℃ ~ 1083 ℃, copper and oxygen form Cu-O eutectic liquid.  DBC technology uses the eutectic liquid to produce chemical reaction with ceramic substrateCualo2 or cual2o4 phase, on the other hand, infiltrate copper foil to realize the combination of ceramic substrate and copper plate.


DPC (Direct Plated copper)

At present, the traditional LC and DBC technology is gradually replaced by DPC, and the laser technology is more in line with the high-density interconnection and fine development of printed circuit boards. The results show that the ceramic circuit board with laser drilling technology has high bonding force between ceramic and metal, no shedding and bubbling, and can grow together. The surface roughness is high, the roughness is between 0. 1 μm ~ 0. 3 μm, and the laser hole diameter is 0. 15 mm-0. 5 mm, or even 0.6 mm.

DBC is the combination of Al2O3 and Cu plate by high temperature heating.  The technical bottleneck of DBC is that it is difficult to solve the problem of micro pores between Al2O3 and Cu plate, which makes the mass production energy and yield of the product face great challenges.  However, DPC technology uses direct copper plating technology to deposit Cu on Al2O3 substrate.  Its process combines materials and film technology, and its products are most commonly used in recent yearsCeramic heat dissipation substrate. However, the requirement of material control and process technology integration ability is high, which makes the technical threshold of entering DPC industry and stable production relatively high.


Lam technology

Lam technology is also called laser rapid activation Metallization Technology.

Ceramic substrate-our laser rapid activation metallization (LAM) is at the leading level in the global ceramic PCB industry, and can be quickly customized to meet customer needs. Ceramic based substrate has good thermal and electrical properties.  It is an excellent material for power LED packaging, violet light and ultraviolet.  It is especially suitable for the packaging structures of MCM and cob.  It can also be used as the heat dissipation circuit substrate of other high-power semiconductor modules, high current switch, relay and antenna of communication industryFilter, solar inverter, etc.

 

Superiority of ceramic substrate PCB

  • The thermal expansion coefficient of ceramic substrate is close to that of silicon chip, which can save the transition layer Mo sheet, save labor, material and cost;

  • Reduce welding layer, thermal resistance, cavity and improve yield;

  • Only 10. 0% of the printed circuit board with the same line width of 0. 3mm;

  • Excellent thermal conductivity makes the package of the chip very compact, which greatly improves the power density and improves the reliability of the system and device;

  • Ultra thin (0. 25 mm) ceramic substrate can replace BeO without environmental toxicity;

  • The temperature rise is about 17 ℃ when 100A current continuously passes through a copper body with a width of 1 mm and a thickness of 0. 3 mm; a current of 100 a continuously passes through a copper body with a width of 2 mm and a thickness of 0. 3 mm, and the temperature rise is only about 5 ℃;

  • The thermal resistance of 10 × 10 mm ceramic substrate is low.  The thermal resistance of 0. 63 mm thick ceramic substrate is 0. 31 K / W, that of 0. 38 mm thickness ceramic substrate is 0. 19 K / W, and that of 0.25 mm thickness ceramic substrate is 0. 14 K / W.

  • High insulation and withstand voltage ensure personal safety and equipment protection ability. 

  • New packaging and assembly methods can be realized to make the product highly integrated and reduce the volume

 

PS: Comparison of thermal properties (conductivity):

Glass fiber substrate (traditional PCB): 0. 5w/mk

Aluminum substrate: 1 ~ 2. 2w/mk,

Ceramic substrate: [alumina] 24 ~ 170 [aluminum nitride] W / MK


Material thermal conductivity (unit: w / MK):

Resin: 0. 5

Alumina: 20-40

Silicon carbide: 160

Aluminum: 170

Aluminum nitride: 220

Copper: 380

Diamond: 600

High thermal conductivity ceramic circuit has the advantages of high thermal conductivity: 25W / m. k, high-voltage resistance: above 12kV, high-temperature resistance: - 55-500 degrees, very small high-frequency dielectric loss, repeated manual soldering without desoldering and delamination, general size: 100 * 160mm.

Double sided copper clad circuit, thickness: 0.25/0.38/0.635/0.8/1.0 mm + 0.2 / 0.3 double-sided copper clad circuit, can be plated with gold/nickel. RoHS compliant

Application of ceramic substrate


  • High power power semiconductor module; semiconductor cooler, electronic heater; power control circuit, power mixing circuit. 

  • Intelligent power module, high frequency switching power supply, solid state relay.

  • Automotive electronics, aerospace and military electronic components.

  • Solar panel module; telecommunication special exchange, receiving system; laser and other industrial electronics.





Comparison of plastics and ceramics

So far, plastics, especially epoxy resin, have dominated the electronic market due to their better economy.  However, many special fields such as high temperature, mismatch of linear expansion coefficient, air tightness, stability and mechanical properties are obviously not suitable.  Even if a large amount of organic bromide is added to the epoxy resin, it will not help.

Compared with plastic materials, ceramic materials have high resistance, outstanding high frequency characteristics, high thermal conductivity, good chemical stability, thermal stability and high melting point. In the design and manufacture of electronic circuits, these properties are very needed.  Therefore, ceramics are widely used as substrate materials for different thick films, thin films and circuits, as insulators, as heat conduction paths in circuits with strict thermal performance requirements, and for manufacturing various electronic components.

Manufacture of ceramic substrate

It is very difficult to produce high-purity ceramic substrate. Most ceramics have high melting point and hardness, which limits the possibility of ceramic machining. Therefore, glass with low melting point is often doped in ceramic substrate for fusing or bonding, so that the final product is easy to be machined. The preparation process of Al2O3, BeO and AlN substrates is very similar. The matrix materials are ground into powder with a diameter of about a few microns, and mixed with different glass fluxes and adhesives (including MgO and Cao of the powder).  In addition, some organic adhesives and different plasticizers are added to the mixture to prevent agglomeration, so that the composition is uniform, and the raw ceramic chips are formed, and finally sintered at high temperature.

 

Relationship between PCB, ceramic substrate and LTCC

LTCC means low-temperature CO firing of ceramics.  Since the maximum sintering temperature of silver is 920 ℃, in order to lay silver wires on the ceramics, low-temperature CO firing is carried out. If silver lines are printed on the inside and on the surface of the ceramics, and they are burned together with the ceramics, that is, the so-called ceramic substrate.  The ceramic plates with two functions of heat dissipation and lead wires on the top and bottom of LED lamps are ceramic substrates.  Of course, there are also those that are not used as substrates.  At present, circuit boards are mostly composed of organic materials. Nowadays, in order to achieve greater integration, many capacitors, resistors and inductors are expected to be integrated into PCB boards.  Most of these are ceramic raw materials and need high-temperature sintering.  We think of ceramic plates with good insulation performance and high-temperature sintering, and the ceramic dielectric constant is adjustable

Difference between ceramic substrate and common PCB

At present, FR-4 circuit board is the most widely used in the market, but the defects of FR-4 circuit board are irreversible. FR-4 copper clad laminate has the advantages of no insulation layer, mass production, fast molding and low price, but the defects are also obvious,

1. Thickness out of tolerance

2. Substrate delamination

3. White spot on substrate

4. Exposed pattern on substrate

5. Impurity and black spot on substrate

6. Copper foil wrinkle

7. Glue spot

8. Pit

9. Pinhole

10. Copper foil oxidation

11. Copper foil bright spot

12. Light concave

13. Steel grain: copper clad laminate with steel plate pattern will cause wavy phenomenon on copper foil surface for fine line PCB production

14. Uneven filling problem

15. Insufficient curing of substrate is obvious, and edge burr is more

16. Common defects of prepreg

17. CAF (substrate resistance to ion migration)


Advantages of ceramic circuit board

1. High resistance

2. Outstanding high frequency characteristic

3. High thermal conductivity

4. Good chemical stability, shock resistance, heat resistance, withstand voltage, internal circuit, mark point, etc.  are better than general circuit board.

5. It is accurate in printing, mounting and welding

Disadvantages of ceramic circuit board

1. Fragile: This is the main drawback, only small area circuit board can be made at present.

2. High price: there are more and more requirements for electronic products.  Ceramic circuit board can only meet the requirements of some high-end products, and low-end products will not be used at all.

 

Ceramic PCB from Rocket PCB

                                                                                 


As for the ceramic substrate, alumina (Al2O3) ceramic circuit board and aluminum nitride (AlN) ceramic circuit board are relatively mature. Many companies can make 3535, 5050, 7070 and so on.  Rocket PCB can be customized by customers.  No matter what specification it is, it can be made.  However, the distance between lines should be greater than 20 microns, and full-automatic production should be adopted.

This kind of products mainly exist in products with high heat dissipation requirements, such as general aerospace, automotive electronics, lighting, high-power electronic components, so as to maximize product performance.


Ceramic PCB industry is estimated to have a market value of 6 billion US dollars in the lighting market, and beat most sunrise industries with an annual growth rate of 7%.  It has become a new high-tech enterprise in the industry, and has been widely used in subway, rail transit, GBT new energy vehicles, etc.

In today's broad market prospects, Rocket PCB focuses on the production of world-class quality ceramic PCB, enhance brand influence, focus on scientific research and development and high-tech application, to provide you with timely, intimate and cost-effective services.

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