Thick Film Ceramic PCB
Thick film technology is employed in the manufacturing process of printed circuit board to enhance the thickness of the conductor layer. Unlike conventional ceramic PCB, which typically have a thickness of around 10 microns, the thick film process enables the attainment of conductor layers that can reach tens or even hundreds of microns. During the implementation of this process, a ceramic PCB utilizes thick film ink to create circuit patterns. The ink is applied onto the ceramic substrate and subsequently subjected to a firing process that facilitates the curing of the applied ink, resulting in the formation of a thick film ceramic PCB. This type of circuit board is also referred to as a thick film resistor ceramic board. Let us now delve into a more detailed understanding of this technology.
Basic Parameter of Thick Film Ceramic Board
- Material: Typically, a thick film ceramic board is fabricated using ceramic materials such as aluminum nitride or alumina. Alumina, owing to its favorable thermal conductivity and electrical insulation properties, is the most commonly utilized material.
- Thickness: The thickness of a board can vary depending on specific applications and requirements. Standard thickness values typically range from 0.2 to 1.5 mm. The conductor layer has a thickness of approximately 10 microns, with a maximum value of 0.02 mm. The minimum trace width is around 0.30 mm, with a corresponding space for larger-scale production of 0.20 mm.
- Dielectric Constant: Also known as relative permittivity, is a key parameter that determines the insulating capability of a ceramic board. It denotes the material’s ability to store electrical energy in the presence of an electric field. Thick film ceramic PCB generally exhibits dielectric constants ranging from 8 to 10 for alumina and 9 to 10 for aluminum nitride.
- Thermal Conductivity: It is a crucial characteristic that defines a material’s ability to conduct heat effectively. It is particularly important for applications requiring efficient heat dissipation. Aluminum nitride-based boards exhibit high thermal conductivity values ranging from 100 to 200 W/mK, while boards based on alumina have thermal conductivities of 20 to 25 W/mK.
- Electrical Resistivity: Refers to the Thick film ceramic based PCB’s ability to impede the flow of electric current. Thick films possess high electrical resistivity, typically ranging from 10^12 to 10^14 ohm-cm.
- Surface Finish: The surface of thick film ceramic PCB boards is often coated with a conductive material, such as gold or silver, to create conductive traces and pads for component connections. The surface finish helps reduce resistance and ensures excellent electrical contact.
|Board Thickness||+/- 10%, Min: +/- 0.08mm|
|Outline to Outline||+0.20mm/-0.05mm|
|NPTH to NPTH||+/- 0.05mm|
|PTH to PTH||+/- 0.10mm|
|NPTH to Edge||+0.15mm/-0.05mm|
|PTH to Edge||+0.20mm/-0.10mm|
Thick Film Ceramic PCB Design Guide
Ceramic PCB Substrate / Raw Material
- The fragile nature of ceramic substrates necessitates the application of thick film technology to enhance their robustness and durability.
- In selecting the raw materials for substrates, careful consideration is given to their thermal and electrical characteristics, taking into account the unique requirements of each specific project.
- Alumina (Al2O3) and Aluminum Nitride (AlN) are frequently chosen as ceramic materials due to their favorable properties and reasonable pricing.
- Ceramics are sought after for their strong dielectric strength, excellent thermal conductivity, and reliable mechanical stability. These attributes serve as fundamental requirements for ensuring optimal performance and functionality.
Conductor Metallization, Trace Layer
- Metalization is employed to form conductive traces on the ceramic substrate.
- Various metals and alloys such as copper, gold, silver, and palladium are utilized to create the conductor layer.
- During the metallization process, a thin coating of the conductive material is applied to the surface of the substrate.
- The trace layer facilitates the transmission of electrical signals between components, enabling the desired flow of electrical currents.
- The concept of “conductor resistivity” describes the inherent resistance exhibited by a material.
- A lower resistance value signifies enhanced efficiency in transmitting signals.
- When it comes to thick film ceramic PCBs, metals like copper and silver are considered optimal choices due to their lower resistance values.
Conductor Power Density
- The maximum power carrying capacity of conductive traces is determined by the conductor power density.
- Conductor power density is influenced by the width, length, and thickness of the traces.
- In order to minimize resistive losses and mitigate the risk of overheating, higher power densities necessitate the utilization of wider and thicker traces.
- In thick film ceramic PCB assembly, bonded resistors are employed to achieve specific resistance values.
- The manufacturing process involves depositing resistor ink onto the substrate, followed by a controlled burning process.
- Bonded resistors offer precise and consistent resistance values, catering to diverse circuit applications.
- To safeguard the electrical traces from solder bridges and environmental influences, a layer of solder mask is applied to the surface of the board.
- A polymer layer is uniformly applied across the entire board surface, with the exception of specific locations where components are to be soldered.
- The solder mask serves the purpose of insulation, providing protection against solder shorts while simultaneously enhancing the durability and robustness of the board.
PTH & NPTH
- Plate-through hole (PTH) is utilized in PCBs to establish electrical connections between different layers.
- To achieve electrical continuity, PTHs are created by drilling holes in the substrate and subsequently depositing a conductive material, often copper, within the hole.
- Non-plated through holes (NPTH), on the other hand, serve purposes such as mechanical support or component mounting, but they lack a deposit of conductive material.
- Manufacturing tolerance refers to the permissible variation from the desired dimensions and specifications during the production of a printed circuit board.
- Thick film ceramic PCB Tolerances are established to ensure consistency and adherence to the design specifications.
- These tolerances encompass critical elements such as dimensions, hole sizes, trace widths, component locations, and other essential parameters.
- By adhering to production tolerances, the reliability and functionality of the printed circuit board is upheld.
How to achieve thick film on ceramic PCB
The production of a thick film ceramic PCB involves a meticulous thick film deposition procedure on a ceramic substrate. This process entails printing a paste-like mixture of ceramic, glass, and metal particles onto the ceramic substrate.
Prior to the deposition, the ceramic substrate undergoes thorough cleaning and polishing to ensure optimal adhesion and surface quality. The thick film ink, often referred to as a paste-like mixture, is then meticulously applied to the substrate utilizing advanced techniques such as stencil printing or screen printing. The ink composition includes conductive substances such as silver, palladium, or platinum, which enhance the electrical conductivity of the circuitry.
The thickness of the thick film layer can be tailored according to the specific requirements of the board. Typically, the thick film layer ranges from a few micrometers to tens of micrometers. By carefully adjusting printing parameters such as screen or stencil thickness, ink viscosity, and printing pressure, the desired layer thickness can be achieved.
Once the thick film ink is deposited on the ceramic substrate, the PCB undergoes a high-temperature firing process in a specialized furnace or kiln. During this firing process, the ceramic particles and metal components in the ink fuse together, resulting in the formation of a robust and durable circuitry layer on the ceramic substrate. Precise control over the firing temperature and duration is crucial to ensure excellent adhesion, stability, and conductivity of the thick film layer.
Upon completion of the firing process, additional steps such as soldering, component mounting, and thorough testing may be performed to finalize the thick film ceramic board assembly.
Thick Film Ceramic Board VS. Ordinary Ceramic Board
|Thick Film Ceramic PCB||Ordinary Ceramic PCB|
|Substrate Material||Alumina (Al2O3), Aluminum Nitride (AlN)||Alumina, Aluminum Oxide, Silicon Nitride|
|Manufacturing Process||Manufactured using advanced techniques such as screen printing and firing. The production process involves the application of conductive and insulating material layers onto the substrate, followed by high-temperature firing to achieve the desired final structure.||Manufactured employing established techniques like dry pressing, tape casting, or green sheet lamination. These sophisticated processes entail shaping the ceramic material into the desired board structure, followed by high-temperature sintering to achieve optimal material consolidation and bonding.|
|Metallization||Gold, Copper, Silver, Palladium||Various metals based on manufacturing process|
|Application Areas||Automotive, Industrial machinery, Aeronautics, Power electronics||Consumer electronics, Telecommunications, Medical instruments, Sensors|
|Design Flexibility||Supports integration of passive components, multilayer designs||Supports multilayer structures, less design freedom compared to thick film ceramic PCBs|
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