What are Ceramic Substrate PCBs

Posted January 3, 2022

Printed circuit boards with ceramic substrates are boards made with a special process where the manufacturer bonds the copper foil directly to the surface of a ceramic substrate made of Aluminum Nitride (AlN) or Alumina (Al2O3). According to Rush PCB Inc., the bonding takes place at a high temperature, and the copper foil may be present on one or both sides of the ceramic substrate, depending on whether the board is single-sided or double-sided.

Importance of Ceramic Substrates

Compared with regular substrates like glass epoxy (FR4) or aluminium (Al), the ceramic substrate is an ultra-thin composite structure. It offers superb electrical insulation, high thermal conductivity, high adhesion strength. Because of these characteristics, a ceramic substrate PCB has higher current carrying capacity, while it is possible to etch it just like a regular board can. With harsh weather resistance capabilities, ceramic PCBs are suitable for harsh outdoor environments. Ceramic PCBs are eminently suitable for product that generate high heat, such as solar energy equipment and high-brightness LEDs do.

Different Ceramic Substrates Available

Alumina (AL2O3): In the electronics industry, this is the most popular substrate material. Compared to several other oxide ceramics, alumina has excellent thermal, mechanical, and electrical properties. Alumina offers high chemical stability and mechanical strength, which makes it suitable for manufacturing many technical equipment in different shapes.

Beryllium Oxide (BeO): Compared to metal aluminum substrates, BeO has a higher thermal conductivity. Its industrial use is mainly for applications requiring high thermal conductivity for temperatures below 300 C, as the thermal conductivity of BeO reduces rapidly above this temperature. However, as BeO is toxic, the industry limits its use.

Aluminum Nitride (AlN): This substrate has two very important properties—its expansion coefficient matches that of silicon, and it has exceptionally high thermal conductivity. However, the presence of even a very thin layer of oxide on the surface reduces the thermal conductivity substantially. Therefore, to fabricate an AlN substrate with proper consistency, manufacturers must strictly control their materials and processes. Another bottleneck restricting the development of AlN is its relatively higher price as compared to that of Al2O3. However, with technological upgrades, the industry expects this bottleneck to reduce.

Of the above types of ceramic substrates, alumina is the most widely used by the industry. It has wide applications in the fields of power electronics, microelectronics, power modules, and hybrid microelectronics. Because of its superior comprehensive performance, alumina is the most widely used ceramic substrate in the electronic industry.

Printed Circuit Boards with Ceramic Substrates

PCB manufacturers use several methods to form boards with ceramic substrates:

Direct Bonded Copper (DBC): The manufacturer deposits a layer of copper on the ceramic material using a eutectic solution of copper and oxygen. A copper deposit forms on the ceramic when there is an optimum proportion of oxygen in the solution and the temperature is between 1065 and 1083 °C. The ceramic material reacts with the eutectic liquid to form copper-aluminum oxide.

Direct Plate Copper (DPC): Manufacturers use professional film manufacturing technology or vacuum techniques for DPC. They clean the ceramic material and bond it with a copper composite layer. They expose the structure to the required trace pattern and develop it with yellow light lithography before etching. After removing the film, the manufacturer increases the copper thickness by electroplating it. They remove the photo-resist, revealing the completed circuit.

Laser Activation Metallization (LAM): In this method, manufacturers use a high-power laser beam to ionize the copper metal and ceramic. The resulting heat causes the copper and ceramic to bond firmly. These boards have superior characteristics, such as:

High-Temperature endurance
Better insulation
Consistent coefficient of thermal expansion
High thermal conductivity
Customizable conductor thickness
High density assembly
low high-frequency losses
No oxide layer formation
Low organic impurities
Low electrical resistance

Thick Film Ceramic: These involve applying a paste of gold conductor material on the ceramic base material. The manufacturer then bakes them at a temperature of about 1000 °C. However, the high cost of gold conductor paste makes this variety of PCBs non-popular.

The main benefits of thick film ceramic as compared to traditional PCBs is the presence of gold does not allow the copper to oxidize. Although the minimum number of layers in a ceramic PCB is two, depending on the requirement, there can be several layers.

Uses of Ceramic PCBs

Memory modules are the main users of ceramic PCBs. These modules are popular in the computer related fields as DDR SDRAM and other forms of memory. Transmission and receiving modules of radar are made using multilayered ceramic PCBs because they need high thermal conductivity and compatible CTE. As it is possible to embed many passive and active components within layers of ceramic PCBs, they offer greater potential for high circuit density. This feature allows using ceramic boards for multi-layered interconnections.

Ceramic PCBs make it possible to realize many other applications that regular PCBs cannot accomplish. These include Analog to Digital converters, solar panels, electric power transmitters, semiconductor coolers, high-power LED boards, and many more.

Conclusion

Rush PCB Inc. recommends using PCBs with ceramic substrates as they offer the unparalleled level of thermal efficiency that most high-temperature devices require. As the substrate itself has high thermal efficiency, the product does not require an additional heat sink for thermal management. Therefore, the semiconductor industry rightly considers the ceramic PCB substrate as their future.