Table of Contents
The modern trends of PCB layers also enable the PCBs to have multiple layers to cater to even more complex designs and miniaturization. Proper layering is beneficial in navigating the transmission and receiving signals and power so that the device performs optimally.
Join ELEPCB, your premier partner, as we guide you through the ultimate perspective on PCB Layers.
What is PCB Layer?
Printed Circuit Boards (PCBs) comprise a plurality of layers, each one of which has a specific role to play. The mentioned layers may vary from one to several and more depending on the hierarchy of the device.This layer of flexibility when applied makes for small and sleek devices, from hand-held mobile devices to medical devices.
PCB Layer Functions and Structures
1 Mechanical Layers
Mechanical layers describe all the external planar surfaces of a PCB starting from its thickness down to the thickness of the copper traces. They include such features as edges of the board, screw holes, and any other openings. These layers help in the PCB manufacturing process as well as assist in organizing the components appropriately on the board.
2 Keep-Out Layers
Keep-out zones define zones on a layer where no component or trace can be placed. This enables the important areas to be left open mechanically or functionally, e.g. connections or areas for heat removal.
3 Signal Routing Layers
These layers have metal tracks that interconnect components on the PCB surface. Connectors and interconnects carry the electrical signals in a circuit, connecting them to the other components of the circuit in the correct manner and with optimum performance.
4 Power and Ground Planes
Power and ground planes are special layers used in the PCB layout, and they act as high current/power paths for power distribution and ground connections. They assist in filtering noise and maintaining consistency by minimizing interference to the current while at the same time providing a good return path to the same source.
5 Split Power and Ground Planes
The ground planes provide some portion of the PCB to have varied power or ground supplies. This separation may minimize the noise levels or separate the analog signals from digital signals or multiple power levels.
6 Solder Mask Layers
The solder mask is a sheet that is applied over the copper lands with the solderable zones being the only visible ones. It avoids the formation of solder between two traces and also shields the PCB against outside factors.
7 Solder Paste Layers
Solder paste depictions show where solder paste should be placed before installing surface-mount parts. Thus, the paste plays a key role in forming a robust connection between the components in the context of reflow soldering.
8 Silkscreen Layers
The text and symbols which need to be printed on the PCB are referred to as silkscreen layers. This refers to labels, reference designators, and other markings that are helpful in assembly, current troubleshooting, and maintenance of electronic equipment.
PCB Layer to Layer
In PCB design, layer-to-layer insulation is a key factor in ensuring proper circuit operation. In multi-layer board construction, layers are physically separated by insulating materials including FR-4, FR-2 and radio frequency (RF) substrates.
These materials not only effectively prevent current leakage, but also improve the overall strength and durability of the PCB, especially FR-4, due to its excellent electrical properties and mechanical strength in the multilayer PCB design has been widely used to significantly improve the reliability and service life of the PCB.
Electrical connection relationship of pcb
(1) Vertical connection
In the multilayer PCB design, vertical interconnection technology is the key to realize the electrical connection between the layers, including through-hole, blind hole and buried holes and other ways.
Through-hole:
Through-hole is the most basic vertical interconnect. It runs through the entire PCB board thickness, to realize the electrical connection between different layers.
Through-hole manufacturing usually use mechanical drilling or laser drilling, and then through electroplating or chemical plating in the hole wall to form a conductive layer.
The advantage of vias is that it is a mature manufacturing process and is suitable for most PCB designs. However, due to their large size, vias may take up more space in high-density wiring.
Blind Vias:
Blind vias are a specialized form of vias-they connect only one outer layer of a PCB to one or more inner layers without penetrating the entire board thickness.
The main advantage of blind vias is that they can significantly improve the space utilization of a PCB (especially in High Density Interconnect (HDI) designs). By using blind vias, designers can realize more complex interlayer connections without increasing the overall size of the IIPCB.
In addition, blind vias can reduce the length of signal paths, thereby improving signal integrity and reducing electromagnetic interference (EMI).
Buried Vias
Buried vias are another more advanced form of vertical interconnection: creating a direct electrical connection between inner layers without the need for a transition through the outer layers. This method not only improves PCB routing density, but also significantly reduces the length of the signal transmission path, thereby improving signal quality and reducing signal delay.
In practice, the choice of these vertical interconnect technologies depends on the specific PCB design requirements and manufacturing process capabilities. For example, high-speed digital circuit design may give priority to the use of blind or buried holes to minimize the signal path length, thereby improving signal integrity; while in high-density packaging (HIP) applications, they may rely more on microvia technology to achieve higher interconnect density and smaller package size.
(2)Interlayer Electrical Isolation
In multilayer PCB design, interlayer electrical isolation is an important factor in ensuring proper circuit operation and improving signal integrity. To realize effective electrical isolation, designers need to consider the following aspects.
1.Impedance control
Impedance control refers to the precise control of the geometric parameters and material properties of the PCB to achieve the desired impedance value, thereby reducing signal reflection and crosstalk.
The core of impedance control is to adjust the width of the signal line between layers and the dielectric constant of the dielectric material. For example, for the inner layer of the signal line, you can use the ribbon line structure, by adjusting the line width, dielectric thickness and ground plane distance to obtain the desired characteristic impedance.
2.Dielectric material selection
Different types of dielectric materials have different dielectric constant and loss factor, will directly affect the effect of electrical isolation between the layers. FR-4 is the most commonly used dielectric materials, but in high-frequency applications, you need to choose a lower loss materials, such as PTFE or ceramic-filled epoxy resin. Because these materials can significantly reduce signal attenuation and distortion, especially suitable for high-speed digital circuits and RF circuit design.
3.Layer structure optimization
Proper layer stacking design can minimize the electrical interference between layers. A common practice is to place the signal layer next to the ground plane layer, thus forming a microstrip line structure, which can effectively suppress radiation and provide a good return path. In addition, it is recommended that high-speed signals are arranged in the inner layer, away from the edge of the board to further reduce EMI.
4.Decoupling capacitor layout
In the power supply layer and ground layer between the reasonable placement of decoupling capacitors can significantly reduce the power supply noise, improve the effect of electrical isolation. The key to this step is to choose the appropriate type of capacitor and capacitance, so that it is close to the corresponding power supply pins.
5.Interlayer shielding
In some special applications, the need to insert a shield between specific layers, such as metal mesh or conductive film, to further enhance electrical isolation. This method is particularly suitable for the need for very high isolation occasions, such as mixed-signal circuits or high-sensitivity sensor interfaces.
How to Plan the Number of PCB Layers?
Determine the number of layers of the PCB board is a tangled and complex process. PCB engineers often hope that the number of layers of the PCB board more good, convenient alignment. Although from the aspect of product performance, multilayer PCE8 board products with good electrical performance, product electromagnetic compatibility is excellent, but from the product cost, the board cycle to assess the number of PCB layers, the more the price is higher, and the board cycle is long.
In determining the number of layers of the PCB board, we need to find a balance among many factors – according to the complexity of the circuit, the density of the device and the initial assessment of special needs.
Determining the number of layers of the PCB board is to ensure that the basic principles of the PCB board to minimize the number of layers under the circumstances of the line, the following aspects:
- (1) By the device layout density to determine the number of PCB layers:
Layout density of the device with the device PIN density to define the PIN density = board area / (total number of pins on the board / 14), the unit of board area is in ². PIN density, the number of signal layers, PCB board layers correspond to the following table.
Table 1: Pin Density, Signal Layers, PCB Layer Correspondence (Single Side)
| PIN density(in ²) | Number of Signal Layers | Number of Board Layers |
| ＞0.8 | 2 | 2 |
| 0.6-0.8 | 2 | 4 |
| 0.4-0.6 | 4 | 6 |
| 0.3-0.4 | 6 | 8 |
| 0.2-0.3 | 8 | 10 |
| ＜0.2 | 10 | ≥12 |
Table 2: Pin Density, Signal Layers, PCB Layer Correspondence (Double Side)
| PIN density(in ²) | Number of Signal Layers | Number of Board Layers |
| ＞0.6 | 2 | 2 |
| 0.4-0.6 | 2 | 4 |
| 0.2-0.4 | 4 | 6 |
| ＜0.2 | 6 | 8 |
- (2) Cost control: If cost is the core consideration, choose single-layer or double-layer boards, the cost increases by about 50% with the number of layers.
- (3) Board-making cycle: If you need to make boards quickly, choose double-layer boards, which have a board-making cycle of 8 to 14 days; multi-layer boards have a longer cycle due to the complexity of the process.
- (4) CPU frequency: when the main frequency is higher than 120MHz, at least use 4-layer boards; below 120MHz, double-layer boards are sufficient.
- (5) Memory type: static SRAM, parallel or serial NOR FLASH for double-layer boards; dynamic SDRAM and NAND FLASH need at least 4-layer boards to support impedance matching and equal-length processing.
- (6) BGA package: If the PIN pitch is ≥0.6mm and the number of PINs is <100, use a double-layer board; otherwise, use at least a 4-layer board.
- (7) Industry characteristics: If the handheld inspection device requires high EMC and ESD protection, use at least 4 layers of boards with a complete ground plane.
Types of PCB Layers
Single-Layer PCB
- A single-layer PCB is completed only on one side of the non-conductive material like fiberglass or epoxy resin with one layer of conducting copper paths. This design is quite basic and suitable for use in designs with few components with little to no need for routing most of the time.
- A single copper layer supports basic electrical connection; however, the construction of the device is simple, and the density of the circuits is low on account of its single-sided structure.
- Single layer PCBs are cheap and easy to produce. However, they are raising issues of space for routing connections, and this limits them from managing complex circuits.
- These PCBs are intended for basic and low-density usage in applications which include basic consumer electronics, educative tools kits, and simple control circuits.
Double-Layer PCB
Construction：
A double-layer PCB has copper foil layers on two sides of a substrate material, whereby the substrate material has electrical conductivity.
Compare to single-layer PCB:
This configuration enables the formation of more complex circuit diagrams compared to single-layer boards as there is an additional surface on which one can make connections. The double-layer PCBs have a higher routing capability and flexibility, which makes them appropriate for complex designs, and they are relatively cheap to manufacture.
Again, double-sided PCBs have higher route density but are still easy and cheap to manufacture. They are one step better than single-layer boards but are less flexible than multilayer boards.
Applications:
This type is widely used in electronic products, industrial control products, and low-end computers.
Multi-Layer PCB
Construction：
Multilayer PCBs are constructed by laminating together a stack of copper and insulating layers and adhering them with an adhesive, just like single-sided and double-sided PCBs.
This construction enables the integration of extremely fine and tightly packed circuitry to design a layout that must have many layers for the routing of signals, power interconnection, and management of the heat produced within the structure.
Multilayer PCBs offer additional layers that increase efficiency in the usage of space and are suitable for high-speed and high-density uses.
Disadvantage:
They integrate very complex circuits and work with high density as well as high signal integrity. Yet they are relatively more costly and difficult to produce as compared to the laminated ones.
Typical Applications:
4Layer PCB: Widely used in those applications where the power and signal must be separated, for example, in the network gear and the state-of-the-art consumer electronics.
6Layer PCB: Applied in advanced apparatuses that require high-velocity signal channelization and segmentation and/or have to be shielded, as computers and communication apparatuses.
8Layer PCB: Most suitable for compact and high throughput designs, including sophisticated medical equipment and contemporary consumer appliances.
Considerations of PCB Layers
Layer Stack-up Configuration
Deciding on the right layer stack-up involves balancing signal integrity, heat dissipation, and cost. Designers must carefully determine how many layers are necessary to route all the signals while also striving to minimize the number of layers to reduce complexity, which in turn helps manage costs.
Signal Integrity and Impedance Control
To understand and maintain signal integrity, firstly, interference must be avoided, and the signals should be delivered over the PCB with little to no distortion. This is made possible with the use of the right layer configuration and routing methods. Signal traces should have controlled impedance to minimize reflections and signal degradation for signals. This is especially so in high-speed and high-frequency application use; sensor technology plays an important role.
Thermal Management
Control of excessive temperature is a critical factor in the management of high-quality and efficient performance. Some Multilayered PCBs incorporate specialized thin layers that are designed to conduct heat to drive heat clear of attractive components.
Cost and Manufacturability
Thus, working with more layers is more expensive and makes the manufacturing process more difficult. This understanding has to be balanced with the additional layers that add benefit, but also cost and production factors engineers agree are necessary.
Conclusion
PCBs and their construction are crucial in today’s world of electronics regarding all sorts of electronics, ranging from the gadgets people use daily to the weaving modern medicine critically relies on.
Single-side PCBs provide basic solutions and are cheaper when compared to double-side PCBs, which are usually more effective in designing complex circuits due to the enhanced layer of routing. Multi-layer PCBs have many layers to support complex circuits and high-density designs to provide high-speed functionality and dissipation of heat. Different power planes in each layer have various purposes and have their benefits and drawbacks as well.
ELEPCB is a reliable PCB manufacturer you can’t afford to miss! With over 10 years of PCB manufacturing experience, we are able to manufacture single-layer PCBs, multi-layer PCBs, laminated PCBs, HDI PCBs and more. From order to delivery, we provide one-stop service with customers all over the world. You can check out our quality control page or just get a quote!
CONTACT US
English 
Italian 
Hungarian