Industry, which needs high-speed, high-frequency boards that can withstand harsh environments, can benefit from ceramic circuit board. Heavy industrial and aerospace equipment can find huge reliability benefits by using ceramic instead of FR4. The main drawback is cost, which can be significant when manufacturing large volumes.
Ceramic vs. FR4
Ceramic plates have some advantages over FR4 plates, which we can take advantage of for certain applications. There is no single material that is ceramic, but this term refers to a series of materials with a similar physical structure and properties. The common ceramic substrate used for circuit boards is aluminum oxide, aluminum nitride, and beryllium oxide. Substrate like silicon carbide and boron nitride are two ceramics with similar performance.
A big difference between FR4 and ceramic materials is their thermal conductivity. FR4 has far less thermal conductivity than the ceramic materials commonly used in circuits. Aluminum oxide is around 20 times more conductive than FR4. Aluminum nitride and silicon carbide conduct 100 times more temperature, and beryllium oxide has even higher thermal conductivity.
Thermal paths, metallic planes in the innermost layers, active cooling elements such as fans and thermal discharges are used to direct the heat from the surface layers to the outside. Ceramic plates do not require these elements, except in extreme cases, and heat can be transported to a thermal discharge, an active cooling element, or the device packaging.
Multilayer ceramic plates
Hybrid multilayer PCB has other benefits especially useful in multilayer layers. Multilayer boards use pathways to more internal layers of the circuit, while pathways in FR4 boards are prone to fracture during thermal cycling. The risk of fracture is due to mismatches in the coefficient of thermal expansion between copper and FR4. The thermal cycling of these plates creates stress on the track path and flat track joints within pads.
When the thermal conductivity is greater in the complete ceramic plate, we ensure that the thermal expansion is also more uniform, avoiding that great stresses are exerted in any of the paths of a specific part of the plate.
Ceramic has desirable mechanical strength and can withstand large mechanical loads, including strong vibrations and shocks. They have a lower modulus of elasticity than FR4, so ceramic plates will tend to deform less than FR4 plates when applying the same force.
Manufacture of ceramic plates
The ceramic plate manufacturing process allows us to use conductive silver or gold pastes by layering the trace connections. These metallic elements or substrate are usually placed on each layer using a layer-by-layer screen printing process. The vias can also be mechanically drilled into a green coat or the micro vias can be laser drilled.