The thermal conductivity and coefficient of thermal expansion (CTE) are the two main properties to focus on when selecting ceramic PCB materials.
Al2O3 ceramic PCBs are used in automobile sensor circuits, shock absorbers, and engines.
Usually, laser rapid activation metallization (LAM) technology is utilized for ceramic PCB manufacturing.
Alumina is the most commonly used ceramic substrate material
Many experts consider ceramic PCBs more advantageous than traditional FR4 PCBs. Even though ceramic PCBs are relatively new on the PCB substrate list, they are gaining popularity for use in high-density electronic circuits. Why? The versatility, durability, stability, and insulation properties offered by ceramic PCBs make them more advantageous than traditional PCBs. And, ceramic PCBs support circuit miniaturization without compromising precision and reliability. In this article, we will discuss the types of ceramic PCBs and learn what makes them so advantageous.
For PCBs placed in environments of high pressure or high temperature, traditional PCB substrate materials may exhibit flaws in extreme conditions. However, ceramic PCB substrate material is suitable for high temperature and pressure as well as corrosive or vibrational circuit conditions. Ceramic PCBs have a high thermal conductivity as well as coefficient of thermal expansion. These PCBs are most suitable for high power density circuit designs that are used in extreme conditions, especially in the aerospace and automotive industries.
Ceramic PCBs are made from a range of ceramic materials. The thermal conductivity and coefficient of thermal expansion (CTE) are the main two properties to focus on when selecting ceramic materials. The ceramic materials used in PCBs refer to a class of substrate materials such as aluminum nitride (AlN), alumina (Al2O3), beryllium oxide (BeO), silicon carbide (SiC), and boron nitride (BN). These ceramic materials share similar chemical and physical properties. Below, we will explore the properties of three common ceramic materials.
Properties of Common Ceramic Substrate Materials
The three most commonly used ceramic materials for PCB manufacturing are:
Alumina (Al2O3) - The mechanical strength, chemical stability, thermal conductivity, and electrical properties of Al2O3 are advantageous compared to other oxide ceramics. The abundance of raw material makes alumina the most commonly used ceramic substrate material. Al2O3 ceramic PCBs are used in automobile sensor circuits, shock absorbers, and engines. The high thermal stability of Al2O3 ceramic PCBs improves the performance and thermal efficiency of the circuits used in automobiles.
Aluminum Nitride (AlN) - The high thermal conductivity and coefficient of expansion are two properties that make AlN noteworthy as a substrate material in the PCB industry. The thermal conductivity of AlN varies in the range of 170 W/mK to 220W/mK. The CTE of AlN ceramic matches with silicon semiconductor chips, which establishes a good bonding between the two, thus making their assembly reliable. AIN is used in sensor circuits in automobiles, as it can withstand extreme temperatures, corrosion, and vibration while providing efficient, accurate, and sensitive sensor signals.
Beryllium Oxide (BeO) - BeO is a ceramic PCB substrate material with a thermal conductivity around nine times that of Al2O3 and greater than metal aluminum. BeO showcases better chemical stability than AlN and high electrical isolation comparable with Al2O3e. BeO is used in applications where the PCB is subjected to high temperatures or in high-density PCBs facing space limitations to provide air or liquid cooling.
Types of Ceramic PCBs Based on Manufacturing Processes
The manufacturing process of ceramic PCBs is simpler than traditional PCBs. Thermally conductive ceramic powder and an organic adhesive are mixed together and thermally treated to fabricate ceramic PCBs. Usually, laser rapid activation metallization (LAM) technology is utilized for ceramic PCB manufacturing. Apart from the ceramic material used, there is one more classification in ceramic PCBs based on the manufacturing process:
- LAM (Laser Activation Metallization) PCB - A high-energy laser is used to ionize the ceramic material and metal in the LAM process. They are grown together, which creates a strong bond between the two.
- Low-Temperature Co-Fired Ceramic (LTCC) PCB - To construct LTCC PCBs, the ceramic material, say alumina, is mixed with a glass material of around 30%-50% quantity. To make the binding proper, organic binders are added to the mixture. The mixture is spread onto sheets to dry and then through-holes are drilled according to the design of each layer. Usually, screen printing is used to print the circuit and fill the holes in LTCC PCBs. LTCC PCB fabrication is finished by heating it in a gaseous oven at 850 ~ 900 ℃.
- High-Temperature Co-Fired Ceramic (HTCC) PCB - HTCC PCBs are made to operate under high temperatures without any damage. The construction of HTCC PCBs starts with fabrication using raw ceramic substrate material, which is not added with glass material at any stage of manufacturing. The HTCC manufacturing process is similar to that of LTCC PCBs with the only difference—the baking temperature of HTCC PCBs is around 1600 ~ 1700 ℃ in a gaseous environment. The high co-firing temperature of HTCC PCBs is so high that metal conductors' high melting points, such as tungsten, molybdenum, or manganese, are used as circuit traces.
- Direct Bonded Copper (DBC) PCB - The DBC process introduces an appropriate amount of oxygen between copper and ceramic before or during the deposition process. The deposition forms Cu-O eutectic liquid at a temperature of around 1065 ℃ ~ 1083℃, and this eutectic liquid is made to chemically react with the ceramic substrate to form CuAlO2 or CuAl2O4. The liquid also penetrates the copper foil and develops a combination of copper plate and ceramic substrate.
- Direct Plate Copper (DPC) PCB - The manufacturing process of DPC utilizes a physical vapor deposition (PVD) method and sputtering to bond copper to substrates under high temperature and pressure conditions.
Ceramic PCBs are well suited for high-temperature, high pressure, high frequency, and high insulation performance. The extensive design, simulation, and analysis features available from Cadence can assist designers in designing PCBs from any material, including ceramics.
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