From Idea to Reality: A Guide to Designing Multilayered ...

Introduction

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Designing a multilayered PCB can be an exhilarating experience for any electronics enthusiast. The thought of bringing to life a complex circuit board that has multiple layers of intricacy and detail can be both daunting and exciting at the same time.

The process of designing a multilayered PCB involves careful consideration of several factors, such as the type of circuit board, the number of layers required, the placement of components, and the routing of traces. It can be a challenging task, but the end result can be incredibly satisfying.In this blog post, we will explain all the fundamental aspects of designing a multi-layered PCB in detail.

If you are designing a printed circuit board (PCB) for your electronic project, you might be wondering whether to use a single-layer or a multilayer PCB. 

A single-layer PCB is a PCB that has only one layer of conductive material, such as copper, on one side of the board. A multilayer PCB is a PCB that has two or more layers of conductive material, separated by insulating layers, such as fiberglass. Multilayer PCBs can have anywhere from four to over 30 layers, depending on the complexity and functionality of the design.

The benefits of using multilayer PCBs are:

- Higher density and complexity: Multilayer PCBs can accommodate more components and connections on a smaller area, which reduces the size and weight of the device. Multilayer PCBs can also integrate different types of circuits, such as analog, digital, and power, on the same board, which simplifies the design and improves the performance.

- Better signal quality and integrity: Multilayer PCBs can reduce the noise and interference between the signals by using shielding layers and ground planes. Multilayer PCBs can also reduce the parasitic capacitance and inductance of the traces, which improves the signal speed and reduces the power consumption.

- Higher reliability and durability: Multilayer PCBs can withstand harsher environments and mechanical stress than single-layer PCBs, because they have more layers of protection and reinforcement. Multilayer PCBs can also reduce the number of connectors and wires, which lowers the risk of failure and improves the reliability.

The differences between single-layer and multilayer PCBs are:

- Cost: Single-layer PCBs are cheaper to manufacture than multilayer PCBs, because they require less materials and processes. However, multilayer PCBs can save costs in other aspects, such as reducing the size of the device, improving the performance and efficiency, and lowering the maintenance and repair costs.

- Design: Single-layer PCBs are easier to design than multilayer PCBs, because they have fewer constraints and variables. However, multilayer PCBs offer more flexibility and creativity in design, because they can accommodate more components and functions on a smaller area.

- Fabrication: Single-layer PCBs are faster to fabricate than multilayer PCBs, because they require fewer steps and machines. However, multilayer PCBs require more precision and quality control in fabrication, because they have more layers and connections that need to be aligned and tested.

Designing the Layers of a Multilayer PCB

A multilayer PCB is a printed circuit board that has three or more conductive copper layers. These layers are separated by layers of heat-protective insulation, such as prepreg (woven glass cloth with epoxy resin) or core (a thin substrate with copper on both sides). A multilayer PCB can have many advantages over a single-sided or double-sided PCB, such as higher density, better signal integrity, lower noise, and reduced size and weight.

However, designing a multilayer PCB also involves some challenges and considerations, such as determining the number of layers needed, planning the layer stack-up, choosing the appropriate materials, and selecting the right thickness for each layer. In this blog post, we will discuss these aspects in more detail and provide some tips and guidelines for designing the layers of a multilayer PCB.

Determining the Number of Layers Needed

The number of layers needed for a multilayer PCB depends on several factors, such as the complexity of the circuit, the electrical requirements, the mechanical constraints, and the cost. Generally speaking, more layers mean more routing space, more shielding options, and more flexibility in design. However, more layers also mean higher fabrication cost, higher parasitic capacitance and inductance, and more difficulty in testing and debugging.

Therefore, it is important to balance these trade-offs and optimize the number of layers for each design. A good rule of thumb is to use the minimum number of layers that can meet the design specifications and performance goals. Some common methods to determine the number of layers are:

- Using a layer estimation formula based on the number of pins, nets, vias, and routing density.

- Using a layer distribution diagram based on the functional blocks and signal types of the circuit.

- Using a layer planning tool that can automatically generate a layer stack-up based on the schematic and layout.

Planning the Layer Stack-Up

The layer stack-up is the arrangement of the conductive and insulating layers in a multilayer PCB. The layer stack-up affects many aspects of the PCB performance, such as impedance matching, crosstalk reduction, power distribution, thermal management, and mechanical stability. Therefore, it is crucial to plan the layer stack-up carefully and follow some best practices, such as:

- Aligning signal layers with reference planes (ground or power) to provide return paths and reduce noise.

- Placing high-speed or sensitive signals on inner layers to avoid interference from external sources.

- Placing power and ground planes close to each other to form a capacitor and reduce noise.

- Placing power and ground planes symmetrically around the core to balance the stress and prevent warping.

- Placing similar signal types on adjacent layers to minimize via usage and improve routing efficiency.

- Placing signals with different frequencies or directions on orthogonal layers to reduce crosstalk.

Choosing the Appropriate Materials

The materials used for a multilayer PCB include copper for conductive layers, dielectric for insulating layers, solder mask for protective coating, and silkscreen for labeling. The choice of materials affects many properties of the PCB, such as electrical performance, thermal performance, mechanical performance, reliability, and cost. Therefore, it is important to choose the appropriate materials for each design based on its requirements and specifications. Some common factors to consider when choosing materials are:

- Dielectric constant: The dielectric constant (Dk) is a measure of how much a material affects the propagation of electromagnetic waves. A higher Dk means slower signal speed and higher impedance. A lower Dk means faster signal speed and lower impedance. The Dk also affects the signal loss and crosstalk. Generally speaking, materials with lower Dk are preferred for high-speed or high-frequency applications.

- Dielectric loss: The dielectric loss (Df) is a measure of how much a material dissipates energy as heat when an electric field is applied. A higher Df means higher signal loss and lower signal quality. A lower Df means lower signal loss and higher signal quality. The Df also affects the thermal performance and reliability of the PCB. Generally speaking, materials with lower Df are preferred for high-speed or high-frequency applications.

- Thermal conductivity: The thermal conductivity (k) is a measure of how well a material conducts heat. A higher k means faster heat dissipation and lower temperature rise. A lower k means slower heat dissipation and higher temperature rise.

Multi-layered PCB

Common Design Challenges and Solutions in multilayered PCBs

Multilayered PCBs are widely used in complex electronic devices that require high performance and reliability. However, designing multilayered PCBs also poses some challenges that need to be addressed carefully. In this blog post, we will discuss some of the common design challenges and solutions in multilayered PCBs, focusing on three aspects: signal integrity, EMI/EMC, and power delivery.

Signal integrity refers to the quality of the electrical signals transmitted through the PCB traces and vias. Signal integrity issues can arise due to various factors, such as crosstalk, impedance mismatch, reflection, attenuation, noise, and distortion. These issues can affect the functionality and performance of the circuit and cause errors or failures. To ensure signal integrity in multilayered PCBs, some of the solutions are:

- Use proper routing techniques, such as minimizing trace length and bends, avoiding parallel traces and stubs, and following the reference planes.

- Use impedance-controlled stackup design, which means matching the characteristic impedance of the traces and vias to the source and load impedances.

- Use termination resistors or capacitors to reduce reflection and ringing at the end of the transmission lines.

- Use differential signaling or shielding to reduce crosstalk and noise coupling between adjacent traces or layers.

- Use signal integrity simulation tools to verify the design before fabrication.

EMI/EMC stands for electromagnetic interference and electromagnetic compatibility. EMI/EMC concerns are related to the generation and susceptibility of electromagnetic radiation from or to the PCB. EMI/EMC issues can cause interference with other devices or systems, violate regulatory standards, or damage the PCB components. To prevent or mitigate EMI/EMC issues in multilayered PCBs, some of the solutions are:

- Use a solid ground plane as a shield against external radiation and a return path for current loops.

- Use decoupling capacitors to filter out high-frequency noise from the power supply lines.

- Use ferrite beads or chokes to block unwanted frequencies from entering or leaving the PCB.

- Use proper grounding techniques, such as avoiding ground loops, using a single-point ground connection, and using vias to connect different ground planes.

- Use EMI/EMC simulation tools or testing equipment to measure and optimize the design for compliance.

Power delivery is the process of providing adequate and stable power to all the components on the PCB. Power delivery challenges can arise due to factors such as voltage drop, IR losses, parasitic inductance and capacitance, switching noise, and thermal effects. These challenges can affect the power quality and efficiency of the circuit and cause instability or malfunction. To overcome power delivery challenges in multilayered PCBs, some of the solutions are:

- Use a dedicated power plane or a thick copper layer to distribute power to all the components with minimal resistance and voltage drop.

- Use multiple vias to connect the power plane to the components and reduce parasitic inductance and resistance.

- Use bypass capacitors to provide local charge storage and smooth out voltage fluctuations caused by switching events.

- Use voltage regulators or converters to adjust the voltage level and provide clean and stable power to different parts of the circuit.

- Use thermal management techniques, such as heat sinks, fans, vents, or thermal vias, to dissipate heat from the PCB and prevent overheating.

What tools can we use to design multi-layered PCBs?

Designing a multilayered PCB is no easy feat. It requires precision, skill, and the right tools to get the job done. Many PCB design software programs are available today, but the two most popular ones are KiCAD and Eagle. In this article, we will discuss whether you can design multilayered PCBs on these two platforms.

KiCAD is a free, open-source PCB design software program that is widely used by both hobbyists and professionals. It has an intuitive user interface and a powerful set of features that make it a popular choice for designing multilayered PCBs. With KiCAD, you can create up to 32 layers in a single PCB, making it ideal for complex designs. KiCAD also has a built-in 3D viewer that allows you to visualize your PCB design in 3D, helping you to identify potential issues before you manufacture the board.

On the other hand, Eagle is a proprietary PCB design software program that is known for its user-friendly interface and extensive library of components. Eagle is widely used in the electronics industry and has been around for over 30 years. With Eagle, you can design up to 16 layers in a single PCB, which is less than KiCAD but still suitable for most multilayered designs. Eagle also has a vast community of users who create and share custom libraries of components, making it easier to find the parts you need for your PCB design.

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At the end of the day, what matters most is not the PCB design software you use but the skill and expertise of the designer. With the right tools and knowledge, we can create high-quality multilayered PCBs that meet our clients' needs and exceed their expectations.

How can Hybrique help you?

Hybrique is a self-contained program that can seamlessly integrate with other software tools, creating a perfect solution for professionals who require collaborative work on complex projects.

The use of Hybrique Plugin empowers you to create a Bill of Materials (BOM) from an existing circuit board. What's more, the application automatically exhibits the most favorable prices from manufacturers and distributors currently obtainable in the market. No more wasting time on manual data entry, as Hybrique automates the process, reducing the chances of inaccuracies and amplifying accuracy.

With the automation features of Hybrique Plugin software, you can ensure that you are always working with the most current and up-to-date information on pricing and availability. The software provides real-time updates, making sure that you are always in sync with the latest data available.

Integrating Hybrique Plugin software into your workflow can significantly improve the efficiency of your engineering and design work. The program's automation and collaboration features, coupled with real-time data updates, ensure that professionals in the industry can work more effectively, resulting in faster and more accurate work.

If you're looking to enhance your workflow and accuracy, the Hybrique Plugin software is the ultimate solution for you. Say goodbye to manual data entry and inaccuracies, and hello to an efficient and collaborative environment. Don't miss out on the opportunity to optimize your engineering and design projects with Hybrique.

If you enjoyed reading our article, please leave a like and let us know what your thoughts are in the comment section.

Introduction

PCB layers can be one or multiple layers of dielectric and conductive materials that are laminated together to make circuit boards used in manufacturing a wide range of electronic devices and machinery across different industries, such as consumer, automotive, telecommunications, aerospace, military, and medical industry.

A printed circuit board is typically made up of copper, substrate, and resin, and is used to connect and support electrical components in electronic devices. The number of layers and dimensions of a particular board determines the PCB's power and capacity. As layers are added, there is increased functionality, offering vast benefits for PCB fabrication and electronics manufacturing. [1]

What are Single-layer PCBs?

The single layer PCB, also known as Single Sided PCB is a circuit board type that is produced with only one layer of conducting material (usually copper) on one side of the board, while the other side is used for attaching different electronic components to the board.

A single-layer PCB, therefore, embodies a substrate layer, a conductive metal layer, a protective solder mask, and silk-screen, which is used to make a complete board consisting of pads, vias, mounting holes, wires, components, connectors, filling, and electrical boundaries.

Single layer PCBs are the foundation of Printed circuit board technology and still play a significant role in the electronics industry.

Advantages of Single Layer PCB

• Low manufacturing cost

• Easier to design with fewer chances of errors

• One layer makes the drilling, soldering, and mounting of components uncomplicated.

• Ideal for low-density designs

• Cost-effective for the production of consumer devices

• Ideal for quick, high-volume production.

Disadvantages of a Single Layer PCB

The simplistic and easily manufactured design of a single-layer PCB may be helpful for users but it also has some impediments.

• Not enough space and connection points for circuit boards that require many components.

• Slower speed and lower operating capacity.

• Added functionality results in a larger size and higher weight, sacrificing compactness.

Single layer PCBs find application in simple home appliances like coffee machines, radios, calculators, as well as camera systems and mobile phones. [2]

What Are Multilayer PCBs?

Multi-layer PCBs are made with double-sided boards that are stacked on top of each other. These stack-ups usually contain three double-sided boards, but they can contain as many boards as needed for a project. However, an odd number of layers could result in twisting or warping after soldering, so it is advisable to use an even number of layers.

Multilayer PCBs are produced by laminating alternating layers of prepreg and core materials under high temperatures. This process ensures that there is no trapped between layers, since conductors are completely covered by resin, and the adhesive that holds the layers together is melted appropriately.  Material combinations for multilayer PCB fabrication range from basic epoxy glass to sophisticated ceramic or Teflon materials, among others.

Applications of multilayer PCBs include computers, file servers, GPS technology, satellite systems, handheld devices, medical equipment like X-ray machines, heart monitors and cat scan technology, nuclear detection systems, space probe equipment, signal transmission, and a host of other high-tech devices.

Advantages of Multilayer Layer PCB

Suitable for complex projects

Multi-layer boards can be expanded by integrating more layers, providing room for additional circuits with extra connections. This makes the board suitable for complex devices that require additional circuits and components.

Durability

The more layers are added, the thicker the board will be,  making it durable. This way, the board can withstand indelicate handling and last longer.

Connection

Several components would usually need more than one connection point, but the multi-layer PCB only needs a single connection point. This advantage is beneficial to producing devices with simple designs and lightweight features.

More Capacity

The extra density of multi-layered PCBs makes them useful for power-intensive devices. So there is increased capacity for powerful devices to operate efficiently.

Disadvantages of Multilayer Layer PCB

More Expensive

Multi-layered PCBs require additional materials, expertise, and time to formulate. Therefore, they cost a lot more than the basic single-layer board. The manufacturer must ensure that the project is well worth the cost of the multilayer board.

Long Lead Time

The intricate demands of the layering process make multi-layer boards take longer to develop. 

The overall completion time is extended due to the number of layers involved in the manufacturing process.

Can be Difficult to Repair

There may be difficulties involved in repairing a problematic multi-layered PCB. This is because some internal layers that are not visible from the outside would make it difficult to locate the source of the issue. The more layers contained on the board, the more complicated it would be to repair. [3]

Due to the difficulty in producing flexible multilayer PCBs, multilayer PCBs are often classified as rigid PCBs. Most of the standard multilayer PCBs have between 4 and 8 layers. Depending on how complicated the application is, smartphones can have up to 12 layers. Also, since laminating an odd number of layers can result in a circuit that is excessively complex and has problems, manufacturers prefer even layers over odd ones. High cost is another consideration to take into account.

Recommended reading: Printed Circuit Boards: Differences Between Rigid, Flex, and Rigid-flex PCBs 

However, the following layer stackings are the layers of a typical multilayer printed circuit board:

2 Layer PCB

The 2-layer PCB is copper coated on both sides with an insulating layer in the middle. It has components on both sides of the board, which is why it is also called a double-sided PCB. They are fabricated by joining two layers of copper together, with a dielectric material in between. The copper on each side can transmit different electrical signals, which makes them suitable for applications where high-speed and compact packaging is essential.

The electrical signals are routed between the two layers of copper, and the dielectric material between them helps to keep these signals from impeding on each other. 2 layer PCBs are the most common and also the most economical boards to manufacture. [4]

4 Layer PCB

4-layer PCBs are printed circuit boards that have four conductive layers: the top layer, two inner layers, and the bottom layer. Both inner layers are the core, usually used as power or ground planes, while the top and bottom outer layers are for placing components and routing signals.

The outer layers are typically covered in solder masks with exposed pads to provide placement spots to attach surface mount devices and through-hole components. Via holes are normally used to provide connections between the four layers, which make a single board when they are laminated together.

Here's a quick breakdown of these layers:

Layer one: This is the bottom layer, normally made of copper. It functions as a base for the entire board, providing support for the other layers.

Layer two: This is the power plane. It is so called because it provides a clean and stable power source for all components on the board. 

Layer three: This is the ground plane layer, which acts as the ground source for all components on the board.

Layer four: The top layer serves to route signals and provides connection points for components.

This is the arrangement for a standard 4-layer PCB stack-up, but it can be switched depending on the design specifications and the layer with the most signals.

4-layer PCBs are much more versatile than traditional 2-layer PCBs, affording a wide range of applications. Also, the additional layers ensure better signal integrity and improved thermal management. For these reasons and more, they are considered more advantageous than 2-layer PCBs. [5]

6 Layer PCB

A 6-layer PCB is essentially a 4-layer board with 2 extra signal layers added between the planes. The 6-layer PCB standard stack-up includes 4 routing layers ( two outer layers and two internal layers) and 2 internal planes (one for ground and the other for power). This amplifies the EMI (Electromagnetic interference) considerably by offering 2 internal layers for high-speed signals and 2 external layers to route low-speed signals. The EMI is the energy that disrupts the signaling in an electronic device through radiation or induction.

There are several arrangements for a 6-layer PCB stack up, but the number of power, signal, and ground layers used is determined by the application requirements. 

The standard 6-layer PCB stack-up includes top layer - prepreg - internal ground plane - core - internal routing layer - prepreg - internal routing layer - core - internal power plane - prepreg - bottom layer. 

Although standard, this arrangement will not be suitable for every PCB design, so there might be a need for reshuffling layer positions or having more of a particular layer. Nevertheless, placements must be done with consideration of routing efficiency and crosstalk minimization. [6]

Planar spiral coil in PCB layer, air-core inductors and surface-mount devices inside RF module of TV receiver

8 Layer PCB

An 8-layer PCB  features four signal layers and four planes that are stacked together. These layers include the ground plane, power plane, and signal layers. The ground and power planes separate and minimize crosstalk between the signal layers. The stack-up of layers on an 8-layer PCB offers quality routing, enhances signal traces, and increases efficiency for complex compact devices.

8-layer PCBs are also beneficial for their high current traces, which are usually very thick and have a low impedance.

Additionally, they provide better power and ground plane separation, increased EMC (Electromagnetic compatibility) performance, and high-speed signal routing. [7]

Conclusion

Decades before now, single-layer PCBs were used in most electrical devices, but the introduction of multilayer PCBs which offer optimized benefits for complex needs took over the industry since the world is getting more technologically advanced. Nonetheless, single-layer PCBs still have relevance for simpler devices, while multilayer PCBs populate high-tech devices.

References

1. PCBA Store. Everything About Printed Circuit Board (PCB) Layers. 2020. [cited 2022 Aug 24]. Available from: https://www.pcbastore.com/blogs/printed-circuit-board-layers-explained.html 

2. The Engineering Projects. Introduction to Single-Layer PCB. 2021. [cited 2022 Aug 24]. Available from: https://www.google.com/amp/s/www.theengineeringprojects.com/2021/11/introduction-to-single-layer-pcb.html/%3famp=1 

3. Electronics And You. Multilayer PCB| Types of PCB| Design, Tutorial, Manufacturing Process. 2021. [cited 2022 Aug 24]. Available from: http://www.electronicsandyou.com/blog/multilayer-pcb.html

4.RayMing. An Introduction to 2 Layer PCB. 2021. [cited 2022 Aug 25]. Available from: https://www.raypcb.com/double-sided-pcb-manufacturer/ 

5. Hillman Curtis. Advantages of 4-Layer PCB Fabrication. 2022. [cited 2022 Aug 25]. Available from: https://hillmancurtis.com/4-layer-pcb/

6. JHY PCB. 6 Layer PCB - Stackup, Thickness, Fabrication, and Price. 2022. [cited 2022 Aug 25]. Available from: https://www.pcbelec.com/pcb-manufacturing/multilayer-pcb/6-layer-pcb

7. Hillman Curtis. 8 Layer PCB Standard Stackup Techniques and Design Challenges. 2022. [cited 2022 Aug 26]. Available from: https://hillmancurtis.com/8-layer-pcb/ 

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