Characteristic Impedance of a PCB Trace
Printed circuit boards (PCBs) are made of metal connections fabricated into the board and known as traces. These are used to carry signals between the various components in the circuit and must be designed with accuracy to achieve optimum performance. One important factor in this is the characteristic impedance of the trace, which influences the amount of current flow. This is determined by a number of factors, including the thickness and dielectric constant of the material and the layer stack-up arrangement.
There are a variety of calculators for determining the characteristic impedance of pcb traces, but the majority of them use formulas that produce up to 7% error. These errors are unacceptable for high-speed and high-frequency applications, and in multilevel signaling protocols with GHz bandwidths. Alternative tools are needed to determine the characteristic impedance of a PCB trace and reduce manual routing time for even the most complex projects.
The function of a trace is to connect any type of electrical signal from one junction to another. This can be an individual component pin or it can be a portion of a larger plane or trace on the circuit board. A trace may also serve as a power signal, carrying current from one power supply terminal to another.
Calculating the Characteristic Impedance of a PCB Trace
In most cases, a trace is a transmission line and must deal with transmission losses, which include both dielectric loss and copper skin effect loss. To mitigate this, the insulating material of the substrate must be carefully selected and chosen to ensure that it has low dielectric loss. Additionally, the copper layer must be thick enough to ensure that it can deliver the required current.
Aside from these factors, there are other considerations that must be taken into account when calculating the characteristic impedance of a PCB signal layer. Coupling between traces must be considered, as well as the coupling between the trace and the reference plane or pad. The layer stack-up arrangement will influence this as well, and ensuring that it is correct is essential to maintaining optimum performance.
The most effective way to calculate the characteristic impedance of a PCB is with a field solver that uses advanced equations to accurately model the entire system. These models are more accurate than traditional formulas and curve-fitting approximations. They can even account for a wide range of fabrication techniques and materials. This allows you to fine-tune your design, ensuring that the traces will be able to meet all your requirements without significant post-design adjustments.
A comprehensive impedance calculator can also help you optimize your circuit layout by allowing you to easily test different variations of your layer stackup and trace widths. You can then select the one that provides you with the most accurate result for your specific application. This will not only improve your performance, but it will also save you valuable design time. For more information on how a PCB impedance calculator can improve your design process, contact us at SierraConnect.
