Introduction
PCBs are coming in various layer configurations in the market. A 6 layers Printed Circuit Board is a type of multilayer PCBs that plays an important role in modern electronics. A stackup of a 6-layers PCB is a masterpiece of technology having a combination of a 4 layers PCB and two signal layers. This article will cover all the information related to 6-layers PCBs in great detail.
Explanation of a 6 Layer PCB
It has six layers. It is a combination of a 4 layers PCB and two signal layers. A common 6-layers PCB stackup has 4 routing layers, 2 outer layers, and 2 internal layers. It has 2 internal planes as well, one for ground planes and the other one for power planes. The design of a 6 layers PCB serves two key functions, firstly of enhancing the electromagnetic interference (EMI) mitigation and the other of optimizing the signal routing.
6 layers PCB diagram
What is a 6 Layers PCB Stackup Made Up Of?
A stackup for a 6 layers PCB consists of several different layers. These layers include the ground plane, the power plane, and the signal layers. Each of these layers serves a specific purpose. It is necessary to understand the important contributions they make to the overall functionality of the 6 layers PCB stackup.
Ground plane
The ground plane is a center for the current to return from different components in the circuit board. This layer has a copper foil connecting to the circuit’s grounding point. It is so flexible that it envelops the entire board. It simplifies the task of grounding components for the manufacturer of the 6 layers PCB.
Power plane
It’s a copper layer that makes a connection with the power source. The power plane delivers the required voltage to the circuit board. It is commonly found in multilayer stacks, especially in those stacks having an even number of layers. The presence of a power plane helps to lower the operating temperature of the board because it can handle the higher current loads in a good way.
Signal layers
This layer consists of the lowermost, uppermost, and the internal layers. All of these layers are interconnected through electricity.
Bottom signal layer
This layer is mainly used for soldering and wiring. In a multilayer board, manufacturers use this layer to attach or solder the components on it.
Top signal layer
It is also called a component layer. This layer is used for arranging copper and circuit wires.
Inner signal layer
It is linked to the power and ground planes. It possesses electrical connections and consists of a complete section made up of copper film. The internal signal layer is present in any multilayer board.
Some ways of Assembly Configuration
In a 6 layers PCB stackup, various arrangements and setups are utilized. Choosing the specific configuration depends on the specific needs and requirements of the application. If the main aim is to achieve more control over the signals, then it becomes vital to increase the number of signal layers. For accommodating the high-speed circuitry, the higher shielding configurations are preferred.
First way
signal1-signal2-GND3-power4-signal5-signal6
First configuration
- Top signal
- Inner signal
- Ground plane
- Power plane
- Inner signal
- Bottom signal
This type of configuration does not provide the necessary protection to signal layers. It was one of the old configurations used in past decades. To minimize mutual interference among signals, PCB manufacturers decrease the range of the bottom and top layers. As signal performance gained importance, manufacturers started to avoid this particular type of configuration.
Second way
signal 1-GND2-signal3-signal4-power 5-signal
Second Configuration
- Top signal
- Ground plane
- Inner signal
- Inner signal
- Power plane
- Bottom signal
The second type of configuration is widely used in industries. It offers effective support for the inner signal layers. It is particularly suitable for the PCBs that have to operate in environments with high signal demands. For the further optimization of the stackup, it is possible to utilize a thicker dielectric material to increase the spacing between the inner signal layers.
Third way
signal1-GND2-signal3-power4-GND5-signal6
Third Configuration
- Top signal
- Ground plane
- Inner signal
- Power plane
- Ground plane
- Bottom signal
In the third type of configuration, each signal layer is placed next to the ground plane ensuring a maximum return path. The position of the ground and power planes in this setup results in planar capacitance.
Fourth way
signal1-GND2-signal3-GND4-power5-signal6
Fourth Configuration
- Top signal
- Ground plane
- Inner signal
- Ground plane
- Power
- Bottom signal
In the fourth type of configuration, each signal layer is placed next to a ground plane. It ensures an optimal return path. The presence of power planes at the bottom along with the signal layer ensures the rise of capacitance from bottom to top. It leads to the minimum number of required signals and capacitance.
Fabrication Method
In the 6-layer PCB fabrication process, some steps should be kept in mind to create the layers and their connection.
Layer Stackup Design
For a 6-layer PCB, this typically consists of signal layers (top and bottom), inner signal layers, and inner ground and power planes.
Material Selection
This is a crucial step in choosing the suitable material. Materials like FR-4 are mostly used for multi-layer PCBs because of their electrical properties and cost-effectiveness.
Inner Layer Processing
We can manufacture the inner layers separately. Copper sheets are laminated onto both sides of a core material and then laminated together to form a solid panel.
Drilling
Small holes called vias are drilled through the panel to connect the different layers. For multi-layer PCBs, both through-hole vias (connecting all layers) and blind vias (connecting some, but not all layers) might be used.
Plating and Copper Deposition
After drilling, the holes are plated with a conductive material to establish electrical connections between the layers. Copper is also deposited onto the circuit traces to enhance conductivity.
Layer Alignment and Bonding
The layers are aligned accurately using automated equipment and then bonded together using heat and pressure to create a single solid structure.
Etching and Lamination
Outer layers are etched to create the desired circuit patterns. Solder mask and silkscreen layers might also be applied. The layers are then laminated together to form the final 6-layers PCB.
Surface Finishing
Surface finishing techniques such as HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), or OSP (Organic Solderability Preservatives) are applied to protect the exposed copper and facilitate soldering.
Testing and Inspection
Various tests like electrical testing, impedance testing, and visual inspection are conducted to ensure the quality and functionality of the manufactured PCB.
Final Cutting and Profiling
The PCB panel is cut into individual boards and the edges are profiled to their final shape.
Conclusion
A close look into a 6 layers PCB shows that it is made up of 4 routing layers, 2 outer layers and 2 internal layers. The layers are stacked in such a way that the 6 layers PCB can lead to the ultimate success of 6-layers PCB design for manufacturers. Thankfully, the latest PCB design tools have the flexibility of adding or removing layers from the design, enabling the manufacturers to choose the most suitable layer configuration for their specific requirements. The main concern for manufacturers is the selection of the design system for their PCB that provides them with maximum power and flexibility through the creation of a 6-layer stackup.
FAQs
What is the standard thickness of a 6 layers PCB?
Standard Six-layer boards have a thickness of 0.031″, 0.040″, 0.047″, 0.062″, 0.093″, and 0.125″ with the same inner layer foil options.
How to make a 6-layer PCB?
The 6 layers PCB can be created by merging signal layers, ground (GND) layers, and power layers. It is important to note that the top layer (layer-1) and bottom layer (layer-6) should be signal layers. The four internal PCB layers can be a combination of two types. The first type includes 2 signal layers, 1 ground layer, and 1 power layer. The second layer consists of 1 signal layer, 2 ground layers, and 1 power layer.
What is a 6-layer PCB material?
A 6 layers PCB board has triple dielectric layers and triple conductive layers. The dielectric layers are made up of fiberglass or other insulating material, while the conductor layers are made up of copper only.
What does a 6-layer PCB mean?
A 6-layer PCB board is actually a 4-layer PCB board having 2 additional signal layers attached between the planes. A common 6-layers PCB stackup has 4 routing layers, 2 outer layers, and 2 internal layers. It has 2 internal planes as well, one for ground planes and the other one for power planes.
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