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High Speed PCB Design Guidelines: Updated 2023

Views: 663 Author: Site Editor Publish Time: 2023-04-25 Origin: Site

High-speed PCB design makes printed circuit boards (PCBs) that work at high speeds, usually hundreds of megahertz or gigahertz. To ensure the plan works well at these frequencies, there are a few things to consider. In this blog, we'll discuss important things to consider when making high-speed PCBs.

Layer stack up A PCB's high-speed performance depends on how its layers are stacked. A good layer stack-up ensures that the signal quality is at its best and that electromagnetic interference (EMI) problems are minimal.

Trace width and spacing:

 The width and spacing of the traces must be carefully chosen to reduce losses and meet impedances. The widths of the traces must be big enough to carry the necessary amount of power while keeping the impedance in check.

Impedance control: High-speed signals need precise impedance control to reduce signal reflections and keep the purity of the signal. Designers must use impedance tools to choose the right widths and thicknesses for the traces and dielectrics to get the right impedance.

It is important to control the impedance when making printed circuit boards (PCBs) for high-speed uses. Impedance control is, in a nutshell, how the resistance, capacitance, and inductance of the lines on the PCB are managed to make sure that signals spread quickly and correctly.

 It is especially important in high-speed digital systems, where signal rise times are very fast and where the effects of signal reflections, Crosstalk, and noise can be very big.

Why PCB impedance is important in PCB?

Impedance is a way to measure how hard it is for electricity to move. In a PCB trace, impedance is decided by the size of the trace, its position in relation to the reference plane (usually a ground plane), the dielectric constant of the PCB material, and the frequency of the signal.

  PCB Design

 Usually, the impedance of a trace is given in Ohms (), and it's important to keep the impedance the same along the length of the trace to avoid signal reflections and Crosstalk.

When a signal comes across a change in resistance along its path, like at the end of a trace or a visa, the signal bounces back. When a signal runs into a change in impedance, some of its energy is sent back to its source. This can mess with other signals on the same trace or worsen the signal's quality. To keep signal echoes to a minimum, the impedance of the trace needs to stay the same along its length.

Conversely, Crosstalk happens when electromagnetic coupling causes two signals on nearby traces to interfere with each other. When a signal on one trace changes quickly, an electric field can cause a voltage in the trace next to it.

This can cause mistakes in the signals and lower the grade of the signals as a whole. To keep Crosstalk to a minimum, keep the distance between the traces the same and use guard traces or insulation to cut down on electromagnetic coupling.

In PCB design, there are several ways to control impedance. One way is to use impedance calculators or field solvers to figure out the needed trace width, spacing, and layer thickness to get the desired impedance.

How to control impedance in PCB?

A popular method is to use controlled impedance traces with a certain impedance value. Most of the time, controlled impedance traces are made by using a certain width and spacing for the traces and changing the thickness of the insulating layer between the signal and ground planes.

Differential signaling, often used in high-speed digital designs, is another way to control resistance. In differential signaling, a signal and its opposite are sent on two lines with a certain amount of space between them. The difference signal has a lower voltage change, which makes noise and interference less of a problem.

Remember that controlling impedance isn't just about ensuring the impedance number stays the same. It also means ensuring that the impedance value fits the system's needs, which can change based on the frequency and type of signal.

For example, high-frequency signals may need a lower impedance to reduce signal loss, while low-frequency signals may need a higher impedance to reduce noise.

In conclusion, controlling impedance is an important part of PCB design for high-speed uses. It means taking care of the resistance, capacitance, and inductance of the PCB traces to ensure that messages travel quickly and don't get messed up. Impedance control helps ensure that high-speed digital systems work well by reducing signal echoes, Crosstalk, and noise.

 Controlling impedance can be done in several ways, such as using controlled impedance traces, differential signals, or impedance calculators. When putting impedance control into their PCB designs, designers need to think carefully about what the system needs and the outputs.

Pairs that are different:

High-speed systems often use differential pairs to reduce electromagnetic interference and improve signal integrity. To get good impedance matching and less Crosstalk, the traces' widths, spacing, and lengths must be carefully controlled.

Placement of vias:

 In high-speed PCB designs, placement of vias is important because they can cause signal reflections and impedance mismatches. When vias are placed carefully, they have less effect on signal stability.

Decoupling capacitors:

These capacitors are used to give the parts on the PCB a stable voltage source. Putting decoupling capacitors in the right place is important to reduce noise from the power source and ensure the system runs smoothly.

Power and ground planes:

 High-speed designs need power and ground planes to ensure the return currents have a way with low resistance. EMI problems can be kept to a minimum, and good signal integrity can be ensured by carefully placing the power and ground planes.

Signal routing is important in high-speed systems because it can greatly impact signal integrity. Routers should be set up so that Crosstalk echoes and losses are minimal.

Handling signals is important in designing printed circuit boards (PCBs). It includes connecting different parts on the board by sending electrical signals through a network of copper traces. The PCB's best performance, reliability, and usefulness depend on how well the signals are routed. This piece will discuss signal routing in PCB design, covering many parts of the process.

Think about signal integrity

Signal integrity is one of the most important things to consider when moving signals on a PCB. It's important to ensure data are sent with as little loss, noise, and distortion as possible. Signal integrity can be affected by many things, such as trace length, routing structure, layer stacking, component placement, and more.

Measure the width and spacing of the traces

The width and spacing of the lines used to route signals are very important for signal integrity to be kept. The current-carrying ability of a trace is based on its width, while Crosstalk and parasitic capacitance are based on the distance between traces. Choosing the right trace width and spacing is important based on what the system needs.

Layer Stackup

When routing data, it's also important to think about how the layers of the PCB are stacked. It decides how many and where the signal and ground planes are, which can greatly affect stability. A well-designed layer stack up can protect well, reduce noise and Crosstalk, and keep signal loss to a minimum.

Component Placement

Signal flow can also be affected by where parts are placed on the PCB. It is important to put components in a way that cuts down on trace length and noise and gives signals a clear path. For the best signal flow, high-speed components like microprocessors and memory chips need to be placed with extra care.

Topology for routing

The routing topology is how the PCB lines are set up. There are different ways to route traffic, such as point-to-point, daisy chain, star, and bus. The choice of routing design is based on what the system needs and what the PCB layout can't do.

EMI shielding

EMI shielding is needed to keep electromagnetic interference from slowing down high-speed data as much as possible. EMI shielding can be done with metal cans or layers of shielding in the PCB stack.

Signal termination is important in high-speed systems so that signal reflections are kept to a minimum and signal integrity is kept. Depending on the type and frequency of the signal, the right termination method, such as series, parallel, or AC termination, must be used.

Signal length matching: Differential pairs need signal length matching to ensure the time is right and reduce skew. The length difference between the differential pair signals must be kept as small as possible to keep signal security as high as possible.

Crosstalk reduction

 In high-speed systems, Crosstalk can greatly affect signal integrity. Crosstalk can be cut down on by ensuring enough space between traces and differential pairs, using guard traces, and using routing methods.

Due to the ground plane's inductance and resistance, high-speed systems can have ground bounce. It is important to use the right methods for decoupling and grounding to keep ground bounce from affecting signal integrity too much.

Thermal management

Designs with a lot of speed make a lot of heat. Heat control tools like heat sinks, thermal vias, and copper pours must be used to ensure components work well and are not damaged.

PCB fabrication

High-speed designs need precise fabrication methods to ensure the required impedance matching, trace widths, and spacing. During PCB manufacturing, choosing the right materials, copper thickness, and surface finishes is important.

About The Author

I am the Engineering and Sales supervisor working in Victorypcb from 2015. During the past years, I have been reponsible for all oversea exhibitions like USA(IPC Apex Expo), Europe(Munich Electronica) and Japan(Nepcon) etc. Our factory founded in 2005, now have 1521 clients all over the world and occupied very good reputation among them.


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