In circuit board factories, there are numerous types of manufacturing technologies for ceramic products; it is said that there are more than 30 different manufacturing processes, such as dry pressing, slip casting, extrusion, injection molding, tape casting, and isostatic pressing, among others. Since electronic ceramic substrates are “flat plate” types (in the form of squares or discs) with relatively simple shapes, and since manufacturing processes such as dry forming and machining are relatively simple and cost-effective, dry pressing is the method most commonly used. This article will explore in detail the manufacturing process of electronic ceramic substrates, including green body fabrication, sintering of green bodies, post-sintering finishing, and the process of forming conductive patterns (circuit lines) on the substrates.
1. Green Body Manufacturing (Shaping)
The manufacturing process for electronic ceramic substrates begins with the production of green bodies, which is the first step in making ceramic substrates.
(1) Manufacturing green bodies using the dry pressing method
Dry-pressed green bodies are formed by mixing high-purity alumina powder (Al₂O₃ content ≥ 95%) with additives (primarily binders, dispersants, etc.) to create a “slurry” or processing material. This slurry is then dry-pressed into green bodies. Currently, the ceramic substrates produced—in the form of squares or discs—can achieve a thickness of 0.50 mm or even thinner (depending on the substrate dimensions).
Dry-pressed green parts can be machined before sintering, such as for external dimensions andDrillingetc., but it is important to note that sintering causes dimensional shrinkage, so dimensional compensation is necessary to maintain accuracy.
(2) Manufacturing green bodies using the cast-filament process
The cast-film method for manufacturing green bodies is an automated, large-scale manufacturing process. It involves uniformly mixing alumina powder with solvents, dispersants, binders, and plasticizers, and then evenly coating the mixture onto a metal or heat-resistant polyester tape using a cast-film machine. This is followed by a series of processes, including drying, trimming, degreasing, and sintering.
2. Sintering of Green Parts and Post-Sintering Finishing
After being manufactured, the green parts must undergo sintering and post-sintering finishing.
(1) Sintering of Green Parts
The sintering of ceramic green bodies is a critical step that involves the volatilization, combustion, and compression of voids, air, impurities, and organic matter within the green body through a high-temperature sintering process to eliminate them, while simultaneously bringing the alumina particles into close contact or causing them to grow together. This process results in changes such as weight loss, dimensional shrinkage, shape deformation, increased compressive strength, and reduced porosity in the sintered body.
There are three methods for sintering ceramic green bodies: atmospheric pressure sintering, pressure (hot-press) sintering, and hot isostatic pressing. Atmospheric pressure sintering is performed without applying pressure, but it may lead to problems such as significant deformation. Pressure (hot-press) sintering is performed under pressure and produces parts with good flatness; consequently, this method is currently the most widely used. Hot isostatic pressing, on the other hand, utilizes high-pressure, high-temperature gas for sintering and is typically used for high-value-added products, such as those in the military sector.
The sintering temperature for alumina green bodies produced by the dry pressing method typically ranges from 1200°C to 1600°C (depending on the composition and flux).
(2) Post-sintering finishing
Sintered ceramic green bodies typically require finishing to achieve a flat surface and a high degree of surface finish. During the high-temperature sintering process, irregularities in the green body—such as uneven particle distribution, voids, impurities, and organic matter—can lead to issues like deformation, surface unevenness, and excessive roughness. These defects can be resolved through surface finishing. Typically, surface polishing involves the use of polishing materials (such as SiC or B₄C) or diamond paste, with the process carried out through successive stages of grinding. Finally, surface treatment is performed using methods such as Al₂O₃ powder with a particle size of ≤1 μm, diamond paste, lasers, or ultrasonic waves to achieve a high surface finish.
In addition, to improve mechanical strength, after surface polishing, ceramic green bodies can be coated with a layer of silicon compounds using methods such as electron beam vacuum deposition, vacuum sputtering, or chemical vapor deposition (CVD) to apply a layer of silicon compound, followed by heat treatment, thereby significantly improving the mechanical strength of the ceramic green parts.
3. Forming conductive patterns (circuits) on the substrate
Finally, to process conductive patterns (circuits) on a ceramic substrate, it is first necessary to manufacture a copper-clad ceramic substrate, and then produce a ceramic printed circuit board using printed circuit board manufacturing techniques.
(1) Forming a copper-clad ceramic substrate
There are two main methods for producing copper-clad ceramic substrates:
- Lamination method: This process involves stacking an activated or roughened ceramic surface with a copper oxide foil and then forming the composite through hot pressing. This method produces products with good flatness.
- Electroplating Process: After the ceramic substrate has been treated, a double-sided copper-clad ceramic substrate is formed through the processes of sputtering titanium, sputtering nickel, sputtering copper, and conventional copper electroplating.
(2) Manufacturing of Single- and Double-Sided Ceramic PCBs
The manufacture of single-sided and double-sided ceramic PCBs follows standard PCB manufacturing processes.
(3) Manufacturing of Multilayer Ceramic Boards
There are two methods for manufacturing ceramic multilayer boards:
- Insulating layers are repeatedly applied to single- and double-sided boards, followed by sintering, wiring, and sintering, to form multilayer boards.
- Ceramic multilayer boards are manufactured using the cast-film method: a green tape is formed on a cast-film machine, and then the process involves drilling, plugging, printing, cutting, laminating, and isostatic sintering to produce the ceramic multilayer board.
In summary, ceramic printed circuit boards are an important type of PCB, offering advantages such as superior thermal conductivity, excellent insulation properties, a high melting point, and thermal dimensional stability. Therefore, ceramic PCBs have broad prospects for development in applications involving high temperatures and high thermal conductivity.
Conclusion
The manufacture of electronic ceramic substrates involves multiple process steps, including green body fabrication, sintering, finishing, and the formation of conductive patterns. These steps require precise control and a high level of expertise to ensure the quality and performance of the final product. Ceramic PCBs offer extensive potential for high-temperature and high-thermal-conductivity applications and will continue to provide reliable solutions for the electronics industry.
Frequently Asked Questions
1. Is the manufacturing process for electronic ceramic substrates complex?
Yes, the manufacture of electronic ceramic substrates involves several complex process steps and requires a high level of expertise and skill.
2. Why is it necessary to sinter ceramic substrates?
Sintering is performed to eliminate voids, air, impurities, and organic matter from the green body, as well as to ensure close contact or intergrowth between alumina particles, thereby improving the quality and performance of the ceramic green body.
3. In which fields do ceramic printed circuit boards have promising applications?
Ceramic printed circuit boards have broad application prospects in high-temperature and high-thermal-conductivity fields, such as aerospace, national defense and military, and nuclear fuel.
4. Why is surface polishing necessary?
Surface polishing produces a smooth surface and a high degree of finish, thereby improving the appearance and performance of ceramic green bodies.
5. What does the future hold for electronic ceramic substrates?
Electronic ceramic substrates will continue to provide reliable solutions for the electronics industry; they hold great potential in high-temperature and high-thermal-conductivity applications and have a bright future ahead.
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