Traditional FR-4 fiberglass boards tend to develop an "arch" shape after reflow soldering. This is an inevitable result of the imbalance between thermal stress and the material's physical properties. Traditional PCBs suffer from component soldering defects and equipment malfunctions due to warping. A type of PCB using ceramic as its substrate, with its near-perfect physical stability, is becoming the core choice for high-power or high-reliability electronic devices.
Why don't ceramic substrates warp?
The root cause of PCB warping lies in the mismatch between the thermal expansion coefficients of the materials and the release of internal stress. Ordinary FR-4 substrates are formed by bonding fiberglass cloth and epoxy resin. The resin softens when heated and shrinks when cooled. Asymmetrical copper foil on both sides further exacerbates the deformation.
Ceramic substrates possess entirely different characteristics. They use high-temperature sintered ceramic green sheets as a base, exhibiting very high elastic modulus and extremely low coefficient of thermal expansion. During manufacturing, copper foil is attached to the ceramic surface via high-temperature hot pressing or direct copper plating technology, achieving intermolecular bonding rather than simple adhesive bonding. This allows the composite structure to maintain dimensional stability even under extreme temperature conditions.
Alumina ceramics: The King of Cost-Effectiveness
Alumina is currently the most widely used ceramic substrate material, containing between 75% and 99.5% alumina. A high purity of 99.5% results in a smooth and dense surface with extremely low dielectric loss, making it suitable for high-frequency circuits.
The thermal conductivity of alumina is approximately 24 to 28 W/(m·K), significantly higher than FR-4's 0.3 W/(m·K). However, it still falls short in ultra-high power applications. It boasts abundant raw materials, high mechanical strength, and excellent chemical stability, making it a prime example of a product that balances performance and cost, thus holding a dominant position in the microelectronics and power module fields.
Aluminum nitride's high thermal conductivity is well-matched to silicon wafers. The emergence of aluminum nitride ceramics has solved the problem of insufficient thermal conductivity in alumina, achieving a thermal conductivity exceeding 170 W/(m·K), seven times that of alumina and even surpassing that of metallic aluminum.
More importantly, aluminum nitride's coefficient of thermal expansion is extremely close to that of semiconductor silicon wafers. When high-power chips are directly mounted on the substrate, the similar expansion coefficient effectively avoids shear stress caused by thermal cycling, thus preventing chip cracking or solder joint fatigue. Its manufacturing process has extremely high requirements for oxygen content control; the lower the oxygen impurities, the stronger the thermal conductivity.
High Thermal Conductivity and Toxicity Limitations of Beryllium Oxide
Beryllium oxide ceramics exhibit exceptional thermal conductivity, even surpassing that of aluminum nitride, reaching over 250 W/(m·K) at room temperature. It was once the preferred material in fields with extremely stringent heat dissipation requirements.
However, beryllium oxide powder is toxic. If the dust generated during production and processing is inhaled, it can cause serious lung diseases. Similarly, if the dust generated during disposal is inhaled, it can also cause serious lung diseases. This fatal flaw severely limits its development. Currently, it is only used in a very few specialized military fields with comprehensive protective measures, and also in a very few specialized aerospace fields with comprehensive protective measures. The civilian market has been largely replaced by aluminum nitride.
The Core Advantages of Ceramic PCBs
The most obvious advantage of ceramic substrates is their strong current-carrying capacity. Experimental data shows that when a 100A current continuously flows through a 1mm thick 0.3mm copper substrate, the temperature rise is only around 17℃. If the copper thickness is increased to 2mm, the temperature rise can be controlled to within 5℃.
In addition, it has excellent insulation properties that can withstand high voltage. This property ensures the safety of equipment and personnel. Because it does not require organic adhesives, its performance is extremely stable in high-temperature and high-humidity environments. Furthermore, the copper foil adhesion is very strong and will not detach due to drastic temperature changes, making its reliability far superior to ordinary PCBs.
Manufacturing Options for Ceramic PCBs
Even though ceramic substrates exhibit superior performance, their fragile nature limits their use in manufacturing large-area boards, and their price is much higher than FR-4. A 100mm side aluminum nitride substrate may cost tens of times more than an FR-4 of the same size.
Therefore, it is mainly used in high-end applications such as high-power LEDs, automotive ignition systems, high-frequency switching power supplies, aerospace, and military electronics. Choosing a ceramic substrate signifies making a choice of ultimate stability and reliability. In actual R&D or small-batch production, selecting a professional and reliable manufacturer is extremely crucial. JEP PCB has been deeply involved in the industry for many years, possessing professional ceramic substrate processing capabilities. From prototyping to mass production, it can provide rapid response and stable process support, ensuring your high-performance design can be accurately achieved.
So, in your product design, will you prioritize cost control, or will you choose a ceramic substrate because of its 5°C temperature rise and unparalleled reliability and stability? Feel free to share your views in the comments section, like and share this article so that more engineers can see this in-depth science popularization.