Loss tangent is omitted: All PCB laminates have some attenuation, which is quantified using the loss tangent.In particular, the above equations are deficient in the following ways: One can show that the above equations are not perfectly accurate, as they include some assumptions that aren’t always true. IPC-2141 trace impedance equations for microstrips and striplines The IPC-2141 impedance equations shown below for microstrips and striplines are based on experimental observations and are reasonably accurate below ~1 GHz. The bare minimum impedance model used in the PCB industry is the formulas in the IPC-2141 standard. The way to calculate the inductance is to first calculate impedance, and then use the impedance to calculate the trace inductance. Other systems, like power converters, may not need controlled impedance along a trace, so they will typically use much larger copper with low inductance. Trace width calculations in transmission line design always start from the perspective of stackup design and selecting a transmission line geometry. With an understanding of the important factors determining the input impedance of a trace, it’s much easier to understand when it’s appropriate to violate impedance goals and opt for a higher or lower trace impedance in your circuit board. In addition, there is no specific rule about what trace inductance you need to use as a design goal for your board. However, there is no specific PCB trace inductance rule of thumb, there are only formulas related to the trace impedance that can be used to determine the trace inductance. While there is no set value of trace inductance you should use, it can be a helpful tool for understanding signal behavior in some systems.ĭo you know the inductance of these traces?Īll PCB traces have some inductance, but do you know how the inductance in a PCB trace affects electrical behavior? Different conductor systems in a PCB need to have particular trace widths, which will determine the inductance of the trace. Sometimes, it’s helpful to understand the inductance of a trace so that you can get an estimate of coupling due to crosstalk. PCB traces have inductance and capacitance, which collectively help determine the impedance of a trace.