The choice of substrate material is critical in determining the electrical performance, mechanical strength, and thermal management of a printed circuit board. Among various substrate materials, ceramics offer exceptional advantages. However, in today’s electronic landscape, there is a growing demand for lightweight and compact PCB boards. Unfortunately, ceramic PCB often face challenges due to their fragility, making it difficult for designers or manufacturers to successfully fabricate multilayer ceramic PCB without encountering processing-related issues and potential damage.
Why Multilayer Ceramic PCB Difficult to Create
Traditional multilayer PCB commonly employ FR-4 or polyimide as substrate materials, which have gained wide acceptance among designers due to their extensive use. On the other hand, ceramic materials like Al2O3 and AlN are also commonly used. However, these materials consist of pure ceramics, making it extremely challenging to construct multilayer circuit structures with them. To address this limitation, the Rogers Corporation developed the Rogers 4000 series, specifically designed for multilayer ceramic circuit boards. These composite ceramic materials have become the preferred choice for designers. However, during the design stage, it is crucial for designers to thoroughly understand the properties and characteristics of different substrate materials to ensure project requirements are met.
Moreover, in addition to adhering to conventional PCB design guidelines such as mitigating electromagnetic interference and optimizing circuit layout, designers must also consider the manufacturing process employed by the manufacturer to enhance compatibility. This process involves additional steps beyond conventional manufacturing, such as powder preparation, molding, and sintering.
For the subsequent assembly process, it is necessary to drill holes in the PCB, which poses challenges when working with ceramic materials due to their inherent brittleness and hardness. When drilling holes, the drill bit penetrates the surface of the ceramic substrate, potentially causing internal structural tearing and resulting in the failure of multilayer ceramic PCB. Furthermore, the high-speed rotation and friction of mechanical drilling generate significant heat, posing an additional significant risk.
One of the primary objectives in designing multilayer circuits is to accommodate a higher number of components on the PCB surface. However, soldering components onto ceramic boards poses significant challenges. Firstly, interlayer connections in multilayer ceramic PCB involve high-temperature and high-pressure lamination processes. Unfortunately, these processes can adversely affect sensitive components, thereby restricting the PCB assembly process. Furthermore, the soldering process requires the use of high-temperature solder alloys and high-temperature solder pastes, which differ from traditional welding materials. Lastly, the high-density arrangement of components results in smaller pitches between them, thereby increasing the difficulty of precise positioning and soldering during assembly.
Why Use Ceramic Multilayer PCB
- Miniaturization: Ceramic substrates are commonly chosen for high-end applications, particularly in the military. However, radar and satellite communication systems demand compact electronics with extensive internal integration. To accommodate a large number of electronic components within a limited space, multilayer circuit structures are indispensable for achieving miniaturization. Moreover, these applications require enhanced signal capabilities, which can be achieved through the use of ceramic PCB.
- Signal Integrity: Ceramic materials exhibit lower loss tangent and dielectric constant compared to other materials, leading to reduced electromagnetic interference and improved signal integrity. As automation technology advances, self-driving cars are gaining popularity, necessitating higher performance. Constructing multilayer Rogers ceramic PCB enhances signal transmission, thereby bolstering the reliability and safety of automation systems.
- Extreme Environments: Industrial systems, including robots, motor drives, power supplies, and control panels, often operate in harsh environments characterized by chemical corrosion and significant temperature variations. Traditional multilayer PCB may not withstand these conditions effectively. In contrast, ceramic multilayer board offer superior heat dissipation performance, resistance to chemical corrosion, and high dimensional stability. This ensures the longevity of electronic applications and mitigates the need for costly replacements of industrial control boards.
Comparison of Different Materials for Multilayer PCB
|Aluminum, Copper, Iron
|Glass Fiber Cloth, Epoxy Resin
|Alumina, AlN, SiC, Rogers
|Moderate: Metal core material in MCPCB can introduce challenges during drilling and cutting processes.
|Simple: Widely used PCB type that is easier to design, manufacture and assembly.
|Hardest: Mainly because it is easily damaged during processing.
|1.0 to 8.0 W/mK
|0.2 to 0.5 W/mK
|20 and 200 W/mK
|-40°C to 150°C
|-40°C to 130°C
|-50°C to 400°C
|Thermal Expansion Coefficient
|10 to 20 ppm/°C
|13 to 18 ppm/°C
|5 to 10 ppm/°C
|150 to 500 MPa
|300 to 500 MPa
|400 to 700 MPa
|1.0×10^5 to 5.0×10^6 S/m
|1.0×10^3 to 1.0×10^5 S/m
|1.0×10^-6 to 1.0×10^-3 S/m
|0.1% to 0.2%
Note: The above is a general situation, and there will be differences according to different designs, raw materials, manufacturing processes, etc.
How to Ensure the Manufacturing Quality of Multilayer Ceramic PCB
Mitigating the failure of multilayer ceramic printed circuit boards is crucial for both PCB manufacturers and electronics manufacturers. Here are some recommended practices:
- Material selection: TechSparks recommends using Rogers laminates as the substrate material for multilayer ceramic PCBs. These laminates offer easier processing and possess desirable properties.
- Appearance inspection: It is essential for the chosen ceramic PCB manufacturer to implement stringent appearance inspection procedures to prevent failures or delivery delays. This can be achieved through methods such as automated optical inspection (AOI), X-ray inspection, manual inspection, etc. These quality control measures should be integrated throughout the entire production process to identify any potential issues, such as cracks.
- Functional testing: After the completion of bare board manufacturing and PCBA manufacturing, functional testing is imperative to ensure that the multilayer ceramic circuit board performs its intended functions. Various testing methods, including electrical testing and flying probe testing, should be employed. Although these tests may introduce some project delays, they are necessary to ensure the reliability and performance of the PCB.
In conclusion, multilayer ceramic PCB offers numerous advantages as outlined above. However, it is important to carefully consider whether they are truly necessary for your design due to their relatively higher cost and complexity in construction. Conduct a thorough assessment of your project requirements and budget constraints before proceeding with the design of the board.