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Why PCB Stacking?

Jan. 28, 2021
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Today's trend towards increasingly compact electronics requires the three-dimensional design of multilayer printed circuit boards. However, layer stacking raises new issues in relation to this design perspective. One of these issues is obtaining high-quality stacked builds for projects.

As PCB manufacturers produce more and more complex printed circuits consisting of multiple layers, the stacking of PCBs is becoming particularly important.

Good PCB stack design is essential to reduce radiation from PCB loops and associated circuits. Conversely, poor stacking can significantly increase radiation, which is harmful from a safety point of view.

What is a PCB stack?

A PCB stack places the insulator and copper of the PCB in layers before the final layout design is completed. Developing an effective stack is a complex process. PCBs connect power and signals between physical devices, and the correct layering of board materials directly affects their function.

Why PCB stacking?

Developing PCB stacks is essential for designing efficient circuit boards. PCB stacks offer many benefits as the multi-layer structure improves energy distribution, prevents electromagnetic interference, limits cross-talk and supports high-speed signal transmission.

Although the primary purpose of stacking is to place multiple electronic circuits on a single board through multiple layers, the structure of a PCB stack also offers other important advantages. These include minimising the board's vulnerability to external noise and reducing crosstalk and impedance problems in high-speed systems.

Good PCB stacking can also help to ensure lower final production costs. By maximising efficiency and improving the EMC of the entire project, PCB stacking can be an effective time and money saver.

6-Layer PCB

PCB lamination design considerations and rules

● Number of layers

Simple stacks may include four PCB layers, while more complex boards require specialist sequential lamination. Although more complex, higher layer counts allow designers more room for layout without increasing the risk of encountering impossible solutions.

Typically, eight or more layers are required to obtain the optimum layer arrangement and spacing to maximise functionality. The use of mass planes and power planes on multilayer boards also reduces radiation.

● Layer arrangement

The arrangement of the copper and insulation layers that make up the circuit constitutes the PCB overlap operation. Preventing PCB warpage requires that the layers are arranged so that the cross-section of the board is symmetrical and balanced. For example, in an eight-layer board, the second and seventh layers should be of similar thickness to achieve optimum balance.

The signal layers should always be adjacent to the planes, while the power and mass planes are strictly coupled together. Multiple grounding layers are preferable as they usually reduce radiation and lower the grounding impedance.

● Determine the cabling and through-holes

Designers should route high-speed signals on intermediate layers between layers. This allows the ground plane to provide a shield which contains the radiation emitted from the track at high speed.

The placement of the signal level close to the plane level allows the return current to flow across the adjacent plane, thus minimising return path inductance. There is insufficient capacitance between the adjacent power and ground layers to provide decoupling below 500 MHz using standard construction techniques.

● Spacing between layers

Tight coupling between the signal and current return planes is essential due to the reduced capacitance. The power and grounding layers should also be closely coupled together.

Signal layers should always be close to each other even if they are located in adjacent planes. Close coupling and spacing between layers is essential for uninterrupted signals and overall functionality.

 

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