The following section will highlight the main design challenges when it comes to designing high-speed PCBs
Since even minimal PCB characteristics can affect signal behavior, your manufacturer needs to have tight tolerances. These are tolerances typically for things like controlled impedance traces, board Stackup, and capacitance, and also the overall length and width of marks.
Availability of high-speed material
Beyond certain speeds, you may start to require the use of unique PCB material if the signals get too fast. Standard FR4 based fiberglass is not the best when it comes to designing high-speed boards. A few of the PCB materials used for high-speed designs are enhanced FR-4, Polyamide, PTFE.
Selecting the correct Layer Stackup
Another critical factor, especially in multi-layer boards, is selecting the right Layer Stackup, were to have a thick prepreg layer, where to have your power and ground planes, and also the separation between the sheets. All these factors, when chosen correctly, will improve signal integrity.
Board to Board Interconnections
When a design has multiple high-speed boards that need to be connected, it is essential to use a interconnect that can properly transmit high-speed signals, typically these will be shielded and length matched cables. The connectors would have their pins oriented in a way to minimize and signal losses.
What are the skills of high speed PCB design?
Knowing a design software that is capable of advanced options
High-speed designs require many sophisticated features in your CAD software. Many programs intended for hobbyists may not have these. Web-based suites also don’t usually have advanced options. So one needs to learn and be skilled at a power CAD tool.
A designer needs to know the rules for necessary routine when it comes to high-speed traces. It would include things such as not cutting ground planes and keeping trails short. Keeping digital lines not too close to avoid crosstalk, and shielding any interference producing elements so that signal integrity is not compromised.
Routing traces with controlled impedance
Certain types of signals require impedance matching. These are usually in the order of 40-120 ohms. Characteristic impedance matched hints are Antennae and many differential pairs.
The designer must be familiar with how to calculate trace width and layer stack for required impedance values. If a trace does not have the correct impedance value, the signal can be severely degraded, resulting in data corruption.
Length matching traces
High-speed memory busses and interface buses have many lines. These lines operate at very high frequency, and so the signals must arrive from the sending end to the receiving end at the same time. It requires a feature called length matching. Most common standards define tolerance values that must match length.
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