What Is Considered High-Speed PCB?
Over the past decade, electronic devices have evolved to include many innovative features and be highly efficient while being small enough to fit anywhere. If we go back two to three decades back, we find electronic devices that were extremely simple and didn’t require much to design.
However, today, there is much focus on impedance control and signal integrity. Modern systems and devices demand high-frequency signals, which hardware designers must consider when designing printed circuit boards (PCBs) from the start. With the rising development of electronic technology, the demand for high-speed PCB design has increased drastically.
Since these high-speed PCBs can work with integrated circuits at high speeds, they are less vulnerable to signal reliability, EMI, and EMC issues.
What Is High-Speed PCB Design?
The reliability of your signals is affected by the physical characteristics of your printed circuit board (PCB). These characteristics include packaging, layout, stack up, and interconnection. High-speed PCB design is sought to overcome issues like emissions, delays, reflections, and crosstalk.
What makes high-speed PCB design stand out from the rest is the fact that it pays much attention to these problems. The majority of hardware designers are used to designing simple PCB where they are placing all the focus on routing and component placement. Yet, here are a few more features you need to consider when using a high-speed PCB.
These are questions hardware designers need to ask themselves when planning: where will I place the traces? What is the width going to be? How close will they be to signals? And what are the types of components that will be connected? These considerations will help you achieve an ideal high-speed PCB design.
The Basics of High-Speed PCB Design
Today, the majority of digital designs utilize high-speed and low-speed digital protocols. However, a high-speed PCB has an RF front end for wireless contact and interaction. Even though the majority of the designs start from a schematic, the majority of high-speed PCB
Design is focused on interconnect design, routing, and PCB stack up.
How to Plan Your High-Speed PCB Stack Up And Impedance?
The process for creating your printed circuit board stack up for a high-speed circuit board will define the resistance and the routing. PCB stack-ups of levels dedicated to high-speed signals, ground planes, and power. Moreover, there are various points to consider when assigning layers in a stack-up.
The Size of Your Board and the New Count
You should consider your board’s size and the nets required when working on a PCB layout. A big board will have more area to give you access to the track during the printed circuit board layout, exclusive of using more than a few signal levels.
The Density of the Route
If you’re in a situation where the net count is high and the board size is constrained to a tinier region, there will not be enough space to route around the surface layer. Hence, you will require more internal signal layers when tracers are pushed closer together. If you move onto a small-sized board, you can force a higher routing density.
The Sum of Interfaces
The perfect strategy is to route max two interfaces per layer, keeping in mind the width of the bus (series versus parallel) and the board range. Maintaining most of your signals in a high-velocity digital port on an even level will guarantee reliable impedance, and all signals can see skew.
Rf Signals and Short Speed
Note if there are any RF signals or low and short-speed digital in your designs. If yes, these will take more area on the exterior level that could have been used for a high-velocity bus or mechanisms, and an extra level might be essential.
Power Integrity
The major keystone of power reliability is using a great power plane and ground plane for each voltage level required in your sizable ICs. These are to be located on nearby layers to help guarantee great plane capacity to help stabilize power with dissociating capacitors.
However, more rules must be considered for all high-speed printed circuit board (PCB) types.
- Have the noise created by the power distribution network primarily in transferring power supplies.
- Decrease crosstalk occurrences among adjacent traces. When the signal frequency is high-pitched, capacitive crosstalk sensations are quickly produced as the stimulated existing have a capacitive impendence
- Lessen the impact generated by the ground bounce. These consequences, unswervingly linked to the signal integrity problem, are condensed by fittingly shaping the PCB stack up and decoupling several parts of the PCB.
- Try to acquire the best probable resistance matching
- Offer the appropriate dissolution for every signal line. This aspect, together with controlling the input, load, and transmission impedances, eliminates the signal reflection.
- A greater degree of immunity to electromagnetic interference (EMI) both radiated and concluded
What Skills Are Required for High-Speed PCB Design?
When hardware designers plan on designing a high-speed PCB, they will consider some factors and parameters that comply with the basic PCB design rules and methods.
Here are some of the key high-speed PCB design skills:
Have the Most Innovative Design Software Options Available
Use software that’ll allow you some superior options. Designing high-speed PCB is not easy. It requires many complex features in your CAD software. There may not be many options on various programs that are available. Thus, you need to have a great understanding of a potent CAD tool.
High-Speed Transmitting
A great designer needs to be aware of the rules for basic routing. It is one of the fundamentals for high-speed traces. It also includes keeping trails concise and not cutting ground planes.
Directing Traces With Impendency Power
High-speed PCB requires impedance matching for approximately 40-120 ohms signal. As for the character resistance matched hints, they are transmitters of several variance pairs. A hardware designer must know how to measure trace width and layer stack for crucial impendence values.
With a lack of accurate impendence values, there may be a severe effect on the signal, which might lead to data exploitation.
Length Matching Traces
There is a range of lines in the interface and high-speed memory buses. These lines can work at quite a high frequency. Thus, the signals must move simultaneously from the transmitting terminal to the receiving terminal. Moreover, it requires a feature called length matching. It helps define the tolerance values that need to match length.
Reducing Loop Holes
There are a few tips that are crucial for hardware designers to know. One of them is reducing the loop area in the high-speed PCB. Since there will be a few issues that include EMI and EMC, they must comply with the fundamental rules, including decreasing loop areas, enhancing existing return paths for traces, and stitching vias.
What Are Some High-Speed PCB Considerations?
Some think your devices operate at lower frequencies and your board is not high-speed. However, this is a false assumption. Any printed circuit board (PCB) where you notice that the strength of your signals is not so great and is constantly being affected by the PCB layout is a sign of high-speed board design.
You can measure the signal strength by examining the time it takes for a chip to switch to a digital signal from an off state to an on one. Usually, if the signal pulse rise time is shorter than the time it takes for the signal to propagate, you must consider your PCB as a high-speed circuit. It’s because the whole signal pulse will be on that trace before hitting the end of the trace.
There are a few considerations you need to keep in mind regarding high-speed PCB.
Remember: Your PCB Layout Is of Extreme Importance
It is crucial to have an effective PCB creation in a high-speed circuit board. There might not be a PCB layout at first that hardware designers can consider. However, you might need to invest time and effort in design to achieve the necessary functionality and succeed in PCB fabrication, including abidance and superior planning.
You need to solve all the issues before PCB layout, including all your designing for manufacturing practices (DFM) and taking additional account for high-speed PCB demands. When the testing phase begins, or you start using it in PCB fabrication, a poorly designed layout will lead to functioning issues.
You’ll have to spend more time, money, and effort assessing the issues, reworking and redesigning the PCB shortcomings, and reassembling prototype layouts. Therefore, aim for a high-functioning PCB design.
Design Is of Utmost Significance
High-speed PCB designs pose many restrictions for the designer as they must meet several signal speed demands and match other hardware designs. Thus, it takes a lot out of them and requires them to consider many factors to achieve a successful circuit board with a high-speed circuity.
Some of the factors they need to consider are as below:
Graphic Considerations
You must know that a well-designed diagram is one of the first steps to setting a great foundation for high PCB design. You can add your touch to the schematic design based on what you’ve done. However, usually, the schematic is a way of communicating and connecting with the board.
Moreover, it is of the best ways to present and organize your high-speed design. A wide range of data is available on the schematic design of the board. These include the mandatory component placements, trace lengths, the data of PCB manufacturers, and much more.
Trace Distance Adjusting
You need to adjust the trace lengths. It helps synchronize signal transmission with data lines when you use a high-speed port. If the interface remains at the maximum frequency, it will not work and will fail since it has not been synchronized.
The greater the frequency of the port is, the greater the length-matching demands will be. Therefore, you should tune the lengths of all traces when you have a parallel port. By showing care at this stage, you can achieve the desired lengths within a group of signals.
PCB Materials and Stack-Up Requests for High Speed
Since you need to meet the demand of several signal speeds, your high-speed design will greatly impact your high-speed design. The factors your design affect include how the layer stack is structured and what materials you use to make high-speed PCB.
High-Speed Placement Tactics
With a high-speed placement strategy, you can enhance the component placement with the help of various methods for high-speed design. Moreover, along with improving the component footprint enhancements to attain high speed, altering pad measurements and component clearances reduce high-speed connection lengths.
Disparity Pair And Trace Length Transmitting
It is essential to have the channeling of distinct pairs if you wish to achieve a high-speed PCB design. It helps in pairing signals simultaneously.
Parallelism, Crosstalk, And Impedance Control
There is a range of forces that pose a negative effect on your high-speed PCB design. For this reason, you need to consider a few factors. One of them is learning how to reduce the impact on your design.
Getting Into the Depth of Microstrip And Strip Line
To design a successful high-speed PCB, you must learn and practice the strip line and microstrip routing techniques. They are crucial in achieving high-speed routing. They will provide you with relevant information on all you need about routing high-speed designs.
Channeling Network Topology And Best Transmitting Exercises
Your schematic design needs certain topologies and shapes to achieve the mandatory circuit path for high-speed routing. Also, it is excellent when exploring several methods to route with return paths, trace lengths, escapes, and much more.
Simulators
Simulation provides great benefits in all stages - before the layout begins, during, and after the layout for high-speed design. You need to understand your PCB design software well so you know the tips and tricks that can be utilized to simulate your designs.
What Are the Ideal PCB Material Options?
Your choice of PCB material is extremely important. You can choose an economical and popular substrate material, including the FR-4, which can be utilized for frequencies under one gigahertz. However, you must remember that the speed at which your signal moves depends on the dielectric constant of any material you choose.
You must also look at the layer count and thickness of the material. It will allow you to understand what is required to accommodate all digital signals in your design. If the speed ICs are large with BGA/LGA footprints, they will allow you to see what board size you might need. When doing BGA fanout, you might usually be able to fit two rows per signal layer and ensure to include the power and ground plane layers in your layer count when building a stack up.
The FR4-grade materials can usually be utilized in a high-speed PCB design, given that the routes in-between are short. If they aren’t, there will be a massive loss in your channel, and the components on the recovery end of the channel might not recover the signals. The ideal PCB material is the loss tangent of your PCB laminates. It will help measure losses. However, usually opting for a much lower tangent FR4 laminate is a great place to begin in smaller PCBs.
How to Identify When You Require a High-Speed PCB?
There are a few ways to know that you need a high-speed design. It is best to figure out beforehand
Do You Have a High-Speed Interface In Your Board?
One fast way of identifying whether you must comply with the high-speed design guideline is to see if you have a high-speed interface. It means checking for PCI-e, DDR, or video interactions such as HDMI, DVI, and many more.
However, there are some major high-speed design rules that you need to follow for all the interfaces. Moreover, you should provide the accurate specifications of each data in the documentation.
What Is the Ratio of Your Trace Length to the Wavelength of Signals?
Your printed circuit board (PCB) will require a high-speed design if the wavelength of your message is similar to the trace length. Some criteria, including DDR, necessitate traces that have a length corresponding to little tolerances.
An excellent irregular figure is one in which you trace length and wavelength can control within one order. It is best to check the high-speed designs.
PCB Alongside a Wireless Interface
You should be aware that all printed circuit boards (PCB) have an antenna. It needs to design for high-speed signals regardless of anything via the connector or on the board. It will require to be connected to a certain impedance value for circuit boards with SMA connectors or similar.
What Are the Significant Problems of High-Speed PCB Design?
You must address a few problems when running a high-speed PCB design. They include:
Timing: You must ask yourself if all your PCB signals appear simultaneously as the others. A clock measures all your high-speed signals on the PCB board. Thus, you will most likely receive spoiled data with inaccurate timing.
Integrity: Note if the signals are similar to when they arrived at the end target. If that’s not the case, then know that it indicates your signals have faced some restriction during the way that has destroyed their reliability.
Noise: If your signals are interrupted in their journey from transmitter to receiver, your data might get lost. It is without fault that every PCB emits some noise. However, in the presence of too much noise, there are high chances of your data getting exploited.
Some solutions will allow you to encounter high-speed PCB design along with these problems.
Impedance: With an appropriate resistance between your source and receiver, you can unswervingly affect the superiority and reliability of your signals. It will also impact how delicate your signals are to sound.
Matching: When you’re identical regarding the distances of two joined traces, it will guarantee that your traces reach simultaneously and in great synchronization with your clock frequencies. Matching is one of the most crucial solutions for HDMI, SATA, USB applications, DDR, and PCI Express.
Spacing: The lesser the distance among your traces, the more vulnerable they will become to sound and additional methods of signal meddling. Thus, you need to place your traces at a certain distance which will help in reducing the noise.
Conclusion
Learning about high-speed PCB requires you to know much about the little things in engineering. Secure the integrity of your signals as they make their way along your PCB from point A (the source) to point B (the receiver). Remember key points if you’ve recently been assigned a high-speed design project. It all starts with having a plan.
You need to be clear about the speed of your signals and the type of signal that needs controlling impedances. You also need to pay attention to the way crucial points in your system will be connected and how you must plan your power planes. Only when you have a solid outline can you start designing your high-speed PCB.
