When we require the board to carry more complex circuits, we need to use multilayer PCBs. However, before the design, we must understand the characteristics of multilayer PCBs and the need to pay attention to some points of multilayer PCB design. Below, we will talk in detail about the characteristics of multilayer PCBs and design considerations.
What is multilayer PCB design?
Multilayer PCB design refers to creating a PCB that contains more than two layers of conductive material. Multilayer PCBs are very important for some industrial electronic equipment. Therefore, before the multilayer PCB design, we must understand the characteristics of the multilayer PCB, as well as the design characteristics of the multilayer PCB, to get the ideal multilayer PCB through the multilayer PCB design. Multilayer PCBs offer wide application potential in the intelligence industry and are suitable for use across various fields. You can also read Flex PCB.
Key features of multilayer PCB design
Multilayer PCBs are complex circuit boards that are made of multiple layers of conductive traces that are separated by insulating materials between the layers. The application of these PCBs can be seen in electronic devices with complex circuit designs and limited space capabilities. Some key features of multilayer PCB design and their specifications are listed below.
Layer Stackup
The arrangement of copper layers and insulating material in a piled-up state is known as layer stack-up. For multilayer PCBs, the layer count can go from four to many. In multilayer PCBs, the number of layers is determined by the circuit’s complexity and the required performance standards.
Material choice
The selection of materials used in multilayer PCBs for the substrate and copper layers is very important and should be made precisely for the advanced performance and durability of the PCB. Some of the common material choices when considering multilayer PCB design are:
FR-4 (fiberglass epoxy laminate)
Polyimide (used in the fabrication of flexible multilayer PCB designs).
Other than that, the copper thickness and type of copper used, like plated copper, in this PCB are also considered for the choice of selection.
Software Used
Some specific and specialized software is used for setting up multilayer PCB design. The following software will help in the creation of circuit schematics, draw out the board layout, and help in handling the layering of PCBs. Some design software used for multilayer PCB design includes:
KiCAD
Proteus
Cadence Allegro
Altium Designer
Cadstar
Protel
Designspark
PADS PCB
Sprint-Layout
Routing
Routing is the process of creating connections between components on a PCB. Multilayer PCB design can be more complex for routing because of the multiple layers present in it. We need to consider the signal integrity and EMI during the routing of these PCBs to ensure proper routing procedures.
Power and Ground Planes
To provide stable power distribution and minimize signal loss, some power and ground planes are included via vias inside the layers of the multilayer PCB design.
Impedance Control
Maintaining impedance is crucial for preserving signal integrity in high-speed digital circuits. The desired impedance for signal traces is achieved by using specified trace width, layer thickness, and dielectric properties. Designers will make all the changes according to the design to achieve the anticipated impedance for signal traces in multilayer PCB designs.
Specifications in manufacturing
Multilayer PCBs are fabricated using multiple processes as well. The process includes layer alignment, lamination, plating, drilling, and etching. The manufacturing chart sheets will be developed and provided by designers specifying surface finish requirements, solder mask, and silkscreen options, etc.
Testing and Quality Control
For multilayer PCBs, the methods carried out for testing are electrical testing, impedance testing, and visual inspection. This testing is all carried out to ensure functionality after the multilayer PCB design and the dependability of each multilayer PCB manufactured.
Environmental Concerns
If multilayer PCBs are implemented in consumer electronics or control industries, it is vital to meet certain environmental standards like RoHS (Restriction of Hazardous Substances).
Design Guidelines for Multi-Layer PCBs
Layer Stack-Up Design
Identifying the number of layers needed based on the circuit complexity and signal integrity for multilayer PCB designs is important. The commonly implemented configurations have a layer count of 4 layers, 6 layers, and 8 layers.
The stack-up arrangement for the multilayer PCB design is outlined below.
- For 4-layer PCB: Signal Ground Power Signal
- For 6-layer PCB: Signal Ground Signal Signal Ground Power
- For 8-layer PCB: Signal Ground Signal Power Ground Signal Ground Signal
Rules for Power and Ground Planes
- For multilayer PCB design, use continuous ground planes to reduce noise and deliver a low-impedance return path.
- Also, it is important for multilayer PCB design to prevent splitting ground planes to avoid signal integrity problems.
- Always use power planes in multilayer PCB design that are solid enough to provide stable voltage levels and minimize power supply noise.
- Implementing multiple power planes in the multilayer PCB design for different voltages will also help with uniform power distribution.
Trace Routing
- Trace routing during the multilayer PCB design is done for smaller and wider traces for high-current paths.
- It is important to maintain a consistent trace width and separation to provide controlled impedance.
Impedance Control
- We need to calculate and control the impedance in the multilayer PCB design for high-speed signal traces. We can achieve it by using proper trace width, layer separation, and dielectric materials.
Vias Usage
- Using the minimum number of vias will help reduce signal degradation for the PCB.
- Blind and buried vias are employed in multilayer PCB fabrication to enhance space and signal integrity.
Thermal Management
- During the multilayer PCB design, we need to place thermal vias under heat-generating components to allow smooth heat dissipation. If we use a range of thermal vias, it will help with effective thermal transfer in the PCB.
- Another way to manage heat is by employing heat sinks and thermal planes for components that provide high power. Implementing copper pours will also help to a good extent with heat management.
Design for Manufacturability (DFM)
- This process is carried out by placing the components on top of the layer, which makes assembly and testing more convenient.
- For soldering and rework to be carried out on the PCB, it is essential to leave sufficient space between the components.
- It is better to use standard via sizes to match manufacturing capabilities. Also, it is essential to have adequate spacing between the vias. So, they must be placed in enough space to avoid solder bridges.
- To get better manufacturing efficiency, it is always advisable to keep panel dimensions in mind while in the multilayer PCB design. Also, including fiducial and tooling holes for assembly will help achieve accurate alignment on the board during production.
Design for Testing (DFT)
- While in the multilayer PCB design, it is always necessary to include sufficient test points for in-circuit testing and functional testing.
- While assembling the enclosure, it is vital to check that the test points are accessible and that the test points do not interfere with component placement.
- For easy inspection, it is important to use a clear solder mask opening. Proper silkscreen labeling for component identification is required on the PCB.
Signal Integrity and EMI Considerations
- Multilayer PCB manufacturing requires signal isolation to avoid interference. For that, high-speed and low-speed signals are isolated.
- To reduce EMI (Electromagnetic Interference), shielding and ground planes must be employed in the fabrication of the board.
- Crosstalk minimization is done by maintaining proper spacing between signal traces. Also, to reduce interference, the routing of high-speed signals is done on different layers of multilayer PCBs.
Software Tools and Simulation
- For layout and routing, advanced PCB design software is used. The multilayer PCB designer uses built-in design rule checks (DRC) to ensure that everything is aligned according to multilayer PCB design guidelines.
- The simulation must be done with the help of simulation tools to validate the thermal and signal performance of the PCB. To identify any potential issues that can occur in manufacturing, pre-simulation and post-simulation (in the course of multilayer PCB design) are carried out.
Documentation and Review
- This is one of the basic things to follow while setting up a multilayer PCB design. Here we are provided with detailed documentation, including schematic diagrams, BOM (Bill of Materials), GERBER files, and assembly drawings for the PCB fabrication.
- Feedback is very important to improve the design if needed. Always providing a review will help optimize the multilayer PCB’s overall appearance.
Future Trends in Multi-Layer PCB Design
Augmented Layer Count
As we are able to develop the technology, we will be able to increase the layer count and use it for more complex and powerful devices. The technological advancement, which is going to happen as a future development, will help attain a larger layer count for multilayer PCB designs.
Enhanced Material Usage
The advancement of new materials and their introduction to the multilayer PCB design are going to give the PCBs enhanced properties such as better thermal management, electrical performance, and mechanical strength. The implementation of this advanced material will help increase the performance and reliability of the multilayer PCBs manufactured.
Advancement in Design Tools
The future advancements in design software and tools will help simplify the design process of multilayer PCB design. The more advanced simulation tools and software will provide precise and accurate multilayer PCB designs.
Conclusion
Multilayer PCB design is essential for building compact, high-performance electronic devices that meet today’s demanding technological needs. Understanding the characteristics, careful planning of the layer stack-up, material selection, routing strategies, and maintaining signal integrity are critical steps to achieving a successful multilayer PCB design. Attention to manufacturing, testing, and environmental considerations ensures reliability and longevity of the final product.
As technology continues to evolve, innovations in materials, design software, and manufacturing processes will open new doors for even more complex and powerful multilayer PCBs. By staying updated with best practices and future trends, designers can create highly efficient, durable, and intelligent multilayer PCBs that drive modern electronics forward.
