The importance of printed circuit boards
(PCBs) in various electronic devices is self-evident. As electronic products
become smaller and more powerful, the demand for PCB layers is also increasing.
In the past, a 2-layer or 4-layer PCBs
might have met the needs, but in today's high-speed and high-density designs,
sometimes 8-layer PCBs are obviously more suitable. They not only have stronger
functions, but also can better ensure signal stability and power distribution
efficiency.
This article will introduce to you
exactly what an 8-layer PCB is, what common 8-layer PCB stack-ups there are,
what its standard PCB thickness is, and the key points to note during design
and manufacturing, to help you meet the development requirements of complex
products.
What Is an 8-Layer PCB?
An 8-layer PCB is a circuit board
composed of 8 layers of copper and insulating materials pressed together. These
layers are connected through vias. Its structure usually includes the signal
layer, power layer, ground layer and internal routing layer.
Compared with ordinary circuit boards, the
8-layer PCB allows for more complex routing, helping to design more complex
circuits. It can also make signal transmission more stable and have stronger
anti-interference ability.
The 8-layer PCB is particularly suitable
for high-speed electronic devices with high-performance requirements, such as
servers, medical instruments and communication systems.
Different Types of 8-Layer PCB Stack-Ups
The 8-layer PCB stack-up structure refers
to how the layers inside the PCB are arranged and what each layer is used for.
Different PCB stack-up structures will directly affect the performance of the
circuit board, such as whether the signal will be interfered with, whether the
power supply is stable, or if the board will heat up severely, etc.
Choosing the right 8-layer PCB stack-up
structure can make your PCB signal more stable, enhance its anti-interference
ability, and improve power supply efficiency. The following are several common
8-layer PCB stack-ups and in which scenarios they are suitable for use:
1. Signal / Ground / Signal / Power /
Ground / Signal / Ground / Signal
• Best for designs with high signal
integrity requirements, such as high-speed communication and server
motherboards.
• Benefits: Low interference, stable
signals, ideal for high-speed circuits.
2. Signal / Ground / Signal / Power /
Power / Signal / Ground / Signal
• Suitable for high-speed circuits, such
as high-performance processor boards.
• Dual power layers provide sufficient
current, while two ground layers help reduce noise, ensuring stable operation.
3. Signal / Signal / Ground / Signal /
Signal / Power / Ground / Signal
• Ideal for mixed-signal devices (analog
+ digital), such as audio processing boards.
• The middle ground layer separates
analog and digital signals, preventing crosstalk.
4. Signal / Ground / Signal / Signal /
Signal / Ground / Power / Signal
• Best for wireless or RF devices, such
as Bluetooth/Wi-Fi modules.
• Multiple ground layers enhance
shielding, reduce signal interference, and improve high-frequency signal
clarity.
5. Signal / Power / Ground / Signal /
Signal / Ground / Power / Signal
• Suitable for high-speed digital
circuits.
• Alternating power and ground layers
isolate noise and improve signal integrity.
6. Signal / Ground / Power / Signal /
Signal / Power / Ground / Signal
• Provides flexible routing space and
balanced power distribution.
• Ideal for control boards requiring
multiple functional modules.
Simply speaking, different 8-layer PCB stack-ups
are suitable for different uses. Whether you are doing high-speed signals, a
mixture of analog and digital, or wireless communication, the stack-up
structures are all different. Choosing the right structure makes your 8-layer
PCB more stable, the signal cleaner and the operation more reliable. When
designing, it is essential to select the most suitable stack-up structure based
on specific requirements.
Standard 8-Layer PCB Thickness
The standard PCB thickness of an 8-layer
PCB usually ranges from 1.6mm (63 mil) to 2.4mm (94 mil), depending on the
copper foil thickness and the choice of prepreg/core material. However, the
final thickness may also be affected by the following factors:
• Copper thickness (e.g., 1
oz, 2 oz)
• Dielectric layer spacing
• Material types used in the PCB stack-up
Thicker PCBs have better strength and are
less likely to bend, making them suitable for industrial equipment, while thinner
PCBs are more suitable for small-sized devices, such as mobile phones or
portable devices.
In the actual design, the standard PCB
thickness needs to be determined based on the characteristics of the circuit,
such as whether to control the impedance, whether there is a heat dissipation
requirement, and the production capacity of the factory. Appropriate thickness
can also ensure that the PCB can be smoothly installed into the casing and
connected to the connector without affecting the product assembly.
Key Considerations for 8-Layer PCB Design
When designing an 8-layer PCB, in
addition to meeting functional requirements, it's essential to comprehensively
consider electrical performance, structural stability, and manufacturing
processes. An excellent design must not only perform well but also be
manufacturable, assemblable, and durable.
Here are some key design recommendations:
1. Layer
Arrangement:
A
well-planned 8-layer PCB stack-up ensures proper distribution of
signal, power, and ground layers, optimizing routing efficiency and overall
performance.
2. Impedance
Control:
For
high-speed signals, trace impedance must be strictly matched. It's recommended
to use simulation tools combined with the specific PCB stack-up to
accurately calculate trace width and spacing, ensuring signal integrity.
3. Structural
Symmetry:
Maintaining
symmetry between the upper and lower PCB layers helps prevent warping
or deformation during lamination, improving the mechanical strength of the
final product.
4. Via Design:
Proper
use of through-holes, blind vias, or buried vias according to spatial and
electrical requirements can optimize routing efficiency and reduce signal
interference.
5.
Thermal Management:
High-density
routing and high-power components can lead to localized overheating. Therefore,
effective heat dissipation paths must be designed, such as adding thermal
copper layers or incorporating thermal vias.
6. Material
Selection:
For
applications requiring high-speed or high-frequency signals, prioritize
materials with low dielectric loss and stable performance.
7. Manufacturing
Tolerances:
Sufficient
production tolerances must be reserved in the design to ensure key parameters
like standard PCB thickness align with factory capabilities
and quality standards.
By implementing these measures,
an 8-layer PCB can achieve a good balance between functionality,
reliability, and manufacturability, ultimately ensuring optimal product
performance and quality.
Manufacturing of 8-layer PCB
The manufacturing of an 8-layer PCB
involves sequential lamination of multiple PCB layers under heat and pressure.
Key steps include:
1. Core
and prepreg preparation
2. Inner
layer imaging and etching
3. Layer
stacking and lamination
4. Drilling
and via plating
5. Outer
layer imaging and etching
6. Surface
finish, solder mask, and silkscreen
7. Electrical
testing and quality inspection
Maintaining tight process control during
manufacturing is essential to preserve the integrity of the PCB stack-up,
especially when using advanced materials or fine-line features.
Conclusion
The 8-layer PCB is an ideal choice for
high-performance electronic systems. Through a reasonable design of the 8-layer
PCB stack-up structure, strict control of the standard PCB thickness, and
optimization of the overall PCB stack-up structure, the stability and
performance of the product can be significantly improved.
Whether you're developing medical
electronics, industrial control systems, or networking equipment, mastering the
design and manufacturing of 8-layer PCBs will give your project a technical
edge.
