Although most advanced features such as impedance control and HDI are suitable for 4 layers, their correct implementation and use are mostly found on PCBs with 6 layers and above. But why would you choose a 6-layer PCB instead of a 4-layer or 8-layer PCB? There may be some reasons:

When designing a 4-layer circuit board, due to insufficient wiring space, you added two layers for wiring.

The EMC performance of a 6-layer PCB is much better than that of a 4-layer PCB.

There are too many high-speed signals and their potential crosstalk on the circuit board.

Too many types of power grids are used.

The cost cannot exceed 6 floors.

For this project, 8-layer boards are too complicated.

For whatever reason, the 6-layer PCB achieves a very good balance between cost and allowable complexity. The 6-layer PCB stack can be arranged and combined, making it a versatile choice for various applications.

6-layer PCB has significant advantages, making it a popular choice for complex and high-performance applications. Some of the advantages include:

Enhanced signal integrity: Due to improved shielding performance and stricter impedance control, the signal integrity of a 6-layer PCB is usually much better than that of a 4-layer PCB. Due to improved isolation, an appropriate 6-layer PCB design can also reduce crosstalk.

The ability to use advanced features: Although most advanced features start at layer 4, using them correctly requires at least 6 layers. The following functions of blind holes and buried holes can be achieved on 4 layers for HDI (high-density interconnect), impedance control, and variable copper weight, but for optimal results, it is recommended to use at least 6 layers.

Higher component density: The more layers that can be wired in the inner layer of a PCB, the larger the space for placing components on the top and bottom layers. In addition, using HDI can also increase the density of components on the PCB.

Flexibility in choosing layers: A 6-layer PCB has multiple combinations of grounding, signal, and power layers, and even for dielectrics, you can choose pre impregnated materials and core boards. Stacking options make it a versatile choice for various applications.

There are also quite a few drawbacks to 6-layer PCBs, including:

Fee standard: 6-layer PCB is very expensive. They are expensive not only because they have more layers and therefore require more materials, but also because 6-layer PCBs are mainly used for high-speed or high EMC applications, which typically have higher manufacturing costs.

Complex design and manufacturing: 6-layer PCBs require specialized knowledge in design and manufacturing. The complexity of 6-layer PCB leads to longer manufacturing delivery cycles. Debugging 6-layer PCBs has also become difficult.

A layer stack is an arrangement of dielectric layers and copper layers. Now, among the 6 copper layers, 4 layers are sandwiched between 5 dielectric layers for insulation, which may be core boards or pre impregnated materials (6 layers of PCB can have more than 1 core board), and there are also 2 layers for placing components. Some layer stacks are as follows:

SIG-GND–PWR–PWR-GND–SIG

This type of layer stack is called a symmetric layer stack. This stack is used to manage high-speed signals, as high-speed signals require a ground plane as a reference plane. Components that use high-speed signals typically use two different voltages, so having two independent power layers is very convenient. The use of reference layers at the top and bottom levels allows the use of vias to transmit high-speed signals (although it is never recommended to use vias to transmit high-speed signals).

This type of stack is very common in network switches, where most network switch ICs consume different voltages and require impedance controlled wiring to transmit high-frequency signals.

SIG- GND – PWR – GND – SIG – GND

This type of layer stack is called an asymmetric layer stack. This layer stack may have less wiring space than other layer stacks, but due to its excellent ground shielding, its EMC performance is also outstanding. Please note that all signal and power layers have adjacent ground planes, which provide high EMC and high power integrity for the stack.

If the signal you are processing is very sensitive to EMI, the internal signal layer will be completely sandwiched by the ground layer. To improve EMC in this stack, you may consider using multiple cores (which would increase the cost of 6 layers of PCB). But there is an obvious problem with the stack, as the bottom layer is a ground layer, it may be difficult to effectively place components at the bottom layer, so only the top layer is suitable for placing components.

SIG – PWR – SIG – SIG – GND – SIG

This is one of the most basic layer stacks, and it is also the most likely layer stack to occur after spontaneously changing layers from 4 to 6. Although this layer stack may look tempting due to the abundance of available signal layers, its EMC performance is very poor, and due to poor shielding, it can be considered to have poor layer utilization. This layer stack may only be suitable for PCBs used in pure DC applications or extremely low-speed signal applications.

SIG – GND – PWR – SIG – GND – SIG

This layer stack is an improved version of the previous layer stack. The top and bottom layers of this stack both have a ground reference plane. This stack can be used for high-speed signals with higher IO counts. Suggest using this stack instead of the previous one for better EMC.

The selection of layer stacks is not limited to the above content. You can create a stack based on your understanding of the requirements. Many 6-layer PCB manufacturers offer layer stacks that are much cheaper than custom layer stacks.

Although the options provided by a 6-layer PCB are very flexible, it requires high reliability and cost-effectiveness. Therefore, the designer's job is to use these layers wisely and effectively. Some key points to note before design are:

Layer arrangement: Power and ground layers are crucial for EMC and stable power distribution. The placement of grounding layers is particularly important for shielding and return paths. All high-speed signals require a ground layer to be placed underneath them for better impedance control and signal integrity. Signals sensitive to EMI are typically routed in an inner layer sandwiched between two ground planes to achieve optimal shielding.

High speed signal layout: For different high-speed signals, it is best to use two extreme layers, namely the top and bottom layers of each signal. This will increase insulation and reduce crosstalk between them.

Heat dissipation precautions: When designing PCB with dense components, it is important to maintain appropriate heat dissipation to achieve optimal component performance. Using materials with high conductivity and heavier copper in the main body can help with better heat dissipation. Using better materials and more copper weight in PCBs can even improve signal integrity.

Selection of core material and prepreg: There are also 5 layers of dielectric on a 6-layer PCB. The thickness and properties of dielectrics have a significant impact on EMC and impedance control calculations. The choice of dielectric type (prepreg and core material) and material type can also seriously affect the cost of 6-layer PCB. Suggest making a wise choice.

If pursuing cost-effective FPC manufacturing services, choosing a Chinese manufacturer is the best choice. As a manufacturing powerhouse, China has abundant resources, cheap labor, and a large number of technical personnel. We recommend Haibo, a Chinese FPC assembly service provider with over 10 years of experience, who has performed outstandingly in various aspects

Efficient and reasonable quotation:There is an efficient quotation process to assist you in making decisions, providing reasonable prices and highly competitive quotes in China.
High quality and reliable products:Produce high standard printed circuit boards, manufacture and test according to specifications, international standards, and internal controls, and conduct pre production inspections to ensure robust processes.
Quick and on-time delivery:The assembly equipment is in good condition, with high productivity, minimal downtime, short delivery time, and also provides urgent services.
Timely and effective response:Always respond to customer needs, provide accurate information, answer questions through multiple channels, and offer one-stop services.
Strong technical strength:China's FPC manufacturing technology is leading, and Haibo has a complete SMT solution that covers assembly, inspection, and other capabilities. It also provides prototype production and customization services.