Ultimate Guide to Ceramic PCB Manufacturing Processes
A ceramic PCB is a printed circuit board made from a ceramic substrate, typically aluminum oxide or alumina, distinguishing it from FR4 PCB that utilizes a fiberglass-reinforced epoxy material. Ceramic PCB provides notable advantages such as superior thermal conductivity (alumina: 24-28 W/mK vs. FR4: 0.3-0.4 W/mK), excellent mechanical strength (alumina: 300-400 MPa vs. FR4: 300-400 MPa), and a higher temperature tolerance (alumina: 1600 °C vs. FR4: 130-140 °C).
While FR4 PCB are cost-effective and commonly used for standard applications, the adoption of ceramic PCB becomes prevalent in high-power, high-frequency, and extreme temperature environments. In such cases, where enhanced thermal management (utilizing formulas like q = k * A * ΔT / d) and performance are crucial, the superior properties of ceramic materials outweigh the higher associated costs and more intricate manufacturing processes.
Here is an outline of the manufacturing process followed by FS Tech to ensure the production of high-quality ceramic PCB:
Step 1: Ceramic Substrate Material Selection
There are three primary substrates used for ceramic PCB fabrication: Al2O3, AlN, and BeO. Various manufacturing techniques for ceramic circuit boards rely on specific substrates, each chosen for its unique properties.
The selection of a ceramic substrate for PCB fabrication relies on a nuanced evaluation of several critical conditions and properties necessary for the intended application. It starts by assessing electrical properties like dielectric constant and strength, ensuring the material aligns with the circuit’s electrical demands. Additionally, considering thermal conductivity is crucial for effective heat dissipation in high-power scenarios. Key Substrates for Ceramic PCB:
Aluminum Oxide (Al2O3):
- Dielectric Constant: 9.6–10.2
- Electrical Strength: 15–20 kV/mm
- Thermal Conductivity: 24-28 W/mK
Aluminum Nitride (AlN):
- Dielectric Constant: 8.7–9.3
- Electrical Strength: 15–20 kV/mm
- Thermal Conductivity: 140-170 W/mK
Beryllium Oxide (BeO):
- Dielectric Constant: 6.7–7.2
- Electrical Strength: 40–45 kV/mm
- Thermal Conductivity: 230-330 W/mK
Step 2: Substrate Preparation
Following cutting, thorough cleaning methods, such as ultrasonic cleaning or chemical treatments, remove contaminants and ensure a pristine surface for subsequent processing. Deburring is performed to eliminate sharp edges, while inspections guarantee a flawless surface, crucial for the uniform deposition of conductive layers. Drying the substrate and any required preconditioning steps finalize its readiness, laying the groundwork for successful deposition processes and subsequent manufacturing stages in ceramic PCB production.
Step 3: Deposition of Conductive Layers
a. Inner Layer Printing
Apply a photosensitive film on the laminate to align the design precisely. Upon exposure to ultraviolet light, this film hardens, accurately aligning the board’s blueprint.
b. UV Exposure and Etching
After aligning the resist and the board, subject it to ultraviolet light, hardening the photoresist. Subsequently, clean unwanted copper from the board using an alkaline solution, leaving the hardened photoresist intact.
c. Layer Alignment and Fusion
Prepare for layer fusion by stacking the outer layers with thin aluminum foil on the substrate, comprising copper tracings. Securely bond these layers together on a heavy steel table using clamps and aligning pins. Employ prepreg layers and copper sheets, finally pressing the stack using aluminum foil and a copper press plate, heating and cooling the assembly for fusion.
d. Precision Drilling
Drill precise holes into the assembled board, employing an X-ray locator for accurate drilling spots. Utilize computer-aided drills with air-driven spindles, ensuring each hole is precisely created, supported by buffer materials for a clean bore.
e. Plating and Copper Deposition
Clean the panel thoroughly, subjecting it to chemical baths for copper deposition, ensuring a thin layer (approximately one micron thick) is deposited across the board’s surface. The copper baths cover hole walls, facilitating connectivity between layers.
f. Outer Layer Imaging
Apply photoresist to the panel and expose it to high UV light in a controlled environment. Remove unhardened resist using a machine, ensuring precision in removing undesired materials from the outer layers.
g. Copper Electroplating
Electroplate the exposed sections of the panel with a thin layer of copper, followed by tin plating to remove excess copper from the etching stage.
h. Final Etching
Use chemical solutions to clear excess copper while protecting desired copper areas with tin, establishing proper conducting areas and connections.
Step 4: Component Attachment
The soldering process is a critical divergence. Ceramic substrates necessitate specialized solder paste formulated to withstand higher temperatures required for their soldering. Additionally, stencils used for applying solder paste need customization to account for the thickness and material of the ceramic, ensuring precise application without compromising the substrate’s integrity.
b. Component Placement
Precision in component placement remains paramount but becomes even more critical for ceramic substrates due to their brittleness. Automated pick-and-place systems or manual methods require meticulous handling to prevent any damage to the substrate during placement. Furthermore, specific adhesives compatible with ceramic properties might be employed for certain components or applications, adhering to temperature and bonding requirements unique to ceramics.
c. Temperature Control
Temperature control during reflow soldering is a notable difference. Ceramic substrates necessitate controlled reflow profiles calibrated to their high-temperature tolerance while avoiding excessive thermal stress. Gradual heating and cooling profiles become vital to mitigate thermal shock, preventing potential damage to the ceramic substrate.
d. Post-Attachment Tests
Post-attachment, the gradual cooling of components is crucial to prevent thermal shock on the substrate. Inspection methods like infrared thermography become necessary to verify solder joint integrity without compromising the structural integrity of the ceramic. Functional tests consider the high thermal conductivity of ceramics, ensuring reliable electrical connections despite potential heat dissipation.
Step 5: Testing and Finishing
a. Board Testing
Continuity Check: Verify the continuity of the electrical path across the circuit traces, ensuring there is no break or interruption that could hinder proper signal transmission.
Impedance Measurement: Evaluate the impedance level within the circuitry to ensure it meets the specified design requirements. This is crucial for maintaining signal integrity, especially in high-frequency applications.
Functional Testing: Perform comprehensive functional tests to validate the PCB’s overall functionality. This involves subjecting the PCB to various operational conditions, ensuring it performs as expected under different scenarios. These tests assess the PCB’s response to input signals and its ability to produce the desired output.
b. Board Finishing Testing
Coating Application: Apply a protective coating to shield the PCB from external elements such as moisture, chemicals, or physical damage. Conformal coating services enhance the PCB’s durability and longevity.
Inspection and Quality Assurance: Conduct a thorough visual inspection to detect any defects or irregularities in the protective coating. Advanced inspection techniques like AOI may be employed to ensure precise coating application and coverage.
With the continuous improvement in the performance of modern electronics, the significance of ceramic PCB becomes particularly crucial. This ensures that circuits can operate stably in extremely harsh conditions. However, compared to traditional materials, ceramic substrates are challenging to implement in multilayer configurations. For pure ceramic materials (Al2O3, AlN, and BeO), FS Tech can currently only construct single-layer, double-layer, and double-sided structures. If your project requires a multilayer ceramic PCB, we will use Rogers as an alternative.
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