Notes for PCB stack-up

By Published On: 2024-07-02Categories: Uncategorized0 Comments on Notes for PCB stack-up

Notes for PCB stack-up

Before PCB design, Great PCB engineers will determine the number of PCB layers based on the size of the circuit board, circuit size, and electromagnetic compatibility (EMC) requirements, then determine the layout of electronic components, and finally confirm the division of signal layer, power layer, and stratum. PCB stacking-up design is usually a choice made after considering various factors, and high-speed digital circuits and whisker circuits are often designed with multi-layer PCBs. Here are the considerations when designing the PCB stack-up.

PCB signal, power supply, and ground plane

There are the signal plane, power plane, and ground plane in the multilayer PCB, and the power plane is as close to or adjacent as possible to the ground plane. The ground plane and power plane are equivalent to a large capacitor that favors the PDN. Each signal line forms a symmetric or asymmetric ribbon line, with a reflux layer, which we call the image layer, which is the reference plane. The low impedance of the power layer and stratum, the calculation formula for the impedance of the power layer:

D is the distance between the power supply and the GND, and W is the area.

  1. What is the reference plane

The signal return path on the circuit board is a large area of a metal or flat layer which becomes the reference plane. This is a ground plane and needs to be on adjacent layers of the signal wires and a layer of dielectric between them. For well-defined routing and reference planes, the energy of the signal will be included and will not overflow the plane to reach the next layer in the circuit board stack.

  1. What is the reference plane

The signal return path on the printed circuit board is a large area of metal or flat layer which becomes the reference plane. This is a ground plane and needs to be on adjacent layers of the signal wires and a layer of dielectric between them. For well-defined routing and reference planes, the energy of the signal will be included and will not overflow the plane to reach the next layer in the PCB circuit board stack up.

  1. Define the single power supply reference plane

The use of decoupling capacitance is an important measure to solve the power supply integrity. The decoupling capacitance should only be placed on the top and bottom planes of the PCB. The wiring, pad, and perforation of the decoupling capacitor will seriously affect the effect of the decoupling capacitor. This requires that the wire connected to the decoupling capacitor should be as short and wide as possible, and the wire connected to the hole should be as short as possible.

  1. Define the multiple power supply reference plane

The multi-power source reference plane is divided into several physical areas with different voltages.

  1. Current distribution direction setting

On the same signal plane, most wiring directions should be consistent and orthogonal to the wiring direction of the adjacent signal plane. For example, you can set the wiring direction of one signal plane to the Y-axis direction and the wiring direction of another adjacent signal plane to the X-axis direction.

  1. Use an even number of layers

From the design of the PCB stack-up can be found that the classic layer design is almost all even layers, rather than odd layers, all the conductive planes in the circuit boards are preserved in the core plane, and the core plane material is generally double-sided plate, in the case of making full use of the core plane, the number of conductive planes of the printed circuit board is even.

  1. Cost considerations

From the perspective of PCB manufacturing cost, the cost of multi-layer printed circuit boards is certainly higher than that of single-sided and double-layer circuit boards, and the more layers, the higher the cost.

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