Ceramic PCB vs. FR-4 PCB – what are the advantages

Ceramic PCB vs FR-4 PCB What Are the Advantages

The glass transition temperature (Tg) of traditional green circuit boards can be as low as 130°C. This is a problem in power electronics applications, where the combination of high component density and tight space results in increased temperatures. To avoid premature failure, ceramic substrates are used. So ceramic PCB vs. FR-4 PCB, what are the advantages?

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    Traditional circuit board structure

    FR-4 PCB
    FR-4 PCB

    The vast majority of circuit boards are manufactured using FR-4. It is an inexpensive epoxy resin impregnated fiberglass material that is ideal for undemanding low power applications. This also makes it the first choice for many engineers when developing new circuits. However , three characteristics of FR-4 limit its use in power electronics applications:

    •Low thermal conductivity
    •Low coefficient of thermal expansion (CTE)
    •Low Tg (typically in the range of 130 to 170°C)

    Poor conductivity can cause hot spots on the circuit board. Low CTE results in differential expansion between the board and copper layers, as well as traces, solder joints, and components. A low Tg means that the board will soften and deform at relatively low temperatures.

    While the metal structures on FR-4 boards improve this problem, they also take up space. Radiators and heat sinks can dissipate heat, but require airflow. There is also the question of how to create a good bond between high-power components and heat sinks. Eventually, it became obvious that reliable power electronics required a replacement for FR-4 boards. Then it is the time to explore ceramic substrates.

    Types of ceramic substrates

    Like FR-4, ceramic is a good electrical insulator. But unlike FR-4, ceramic’s thermal conductivity is comparable to aluminum heat sinks.

    There are many different types of ceramics, but three in particular stand out as substrates. They are aluminum oxide (Al2O3), aluminum nitride (AlN) and beryllium oxide (BeO). For each, the traces are formed by screen-printing a conductive metal paste onto the ceramic, which is then baked or fired.

    Ceramic PCB

    Ceramic PCB vs. FR-4 PCB - what are the advantages?

    Ceramic PCB vs FR-4 PCB
    Ceramic PCB vs FR-4 PCB

    The main benefit of switching from FR-4 to ceramic PCB substrates is how ceramic handles high temperatures. The ceramic substrates mentioned above are very good thermal conductors, which means they can better transfer heat from the circuit board device to the heat sink. This also prevents the formation of localized hot spots.

    The second benefit is that the CTE of the ceramic substrate is closer to the CTE of the metal traces on the substrate and the components soldered to the substrate. This helps minimize stresses that can cause components and solder joints to break.

    Because ceramic substrates are better able to conduct heat away from heat sources, they become a more reliable PCB substrate material than FR-4 in power electronics applications and allow designers to achieve higher power density designs. However, ceramics have two other advantages.

    First, in high-frequency power electronics applications, FR-4 PCBs may suffer from parasitic capacitive effects due to the close proximity of traces and components. This hinders high-frequency response and will become a bigger problem as boards become more dense. However, ceramic substrates do not encounter this problem.

    Secondly, the moisture resistance of ceramic is much better than FR-4. FR-4 absorbs moisture, which can be a significant issue in marine and vehicle power electronics applications. In contrast, ceramics do not have such problems.

    Conclusion

    FR-4 has long been the “go-to” material for circuit boards. It performs well in many applications but is challenged by heat and humidity. Many power electronics applications generate large amounts of heat, and using FR-4 substrates represents a long-term reliability risk. Ceramic substrates can protect your devices from premature failure in high power applications. Using ceramic substrates in high-power applications means greater reliability and a smaller product footprint.

    FAQ-about PCB

    FR4 is a class of printed circuit board base material made from a flame retardant epoxy resin and glass fabric composite. FR stands for flame retardant and meets the requirements of UL94V-0. FR4 has good adhesion to copper foil and has minimal water absorption, making it very suitable for standard applications.

    Ceramic PCB is a printed circuit board with ceramic base material, which is highly thermally conductive materials such as alumina, aluminum nitride, as well as beryllium oxide, which can make a quick effect on transferring heat away from hot spots and dissipating it over the whole surface.

    1. Ceramics can handle high temperatures.
    2. The CTE of the ceramic substrate is closer to the CTE of the metal traces on the substrate and the components soldered to the substrate. This helps minimize stresses that can cause components and solder joints to break.
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