Enter the dielectric constant, trace height, trace width, and trace thickness into the calculator to determine the PCB impedance.

PCB Impedance Formula

The following formula is used to calculate a PCB impedance for a microstrip. 

Z = [ 87 / SQRT(e+1.41) ] * ln [ 5.98H / (.8W +T) ]
  • Where Z is the impedance
  • e is the dielectric constant
  • H is the trace height
  • W is the trace width
  • T is the trace thickness

What is PCB Impedance?

PCB impedance refers to the resistance that an electronic signal encounters as it travels through a printed circuit board (PCB). It is a crucial characteristic in determining how effectively signals can be transmitted and received within a PCB.

Impedance is primarily influenced by the physical properties of the PCB, such as its materials and dimensions.

These properties determine the flow of electrical signals and can significantly affect the performance and reliability of the circuit. PCB impedance is measured in ohms and is represented as a complex quantity of resistance and reactance.

Correct impedance prevents signal degradation, reflections, and crosstalk within the PCB. When signals encounter impedance mismatches, they can bounce back and interfere with the original signal.

This can lead to distorted or lost data, resulting in reduced performance or complete circuit failure.

Properly controlling PCB impedance ensures signals propagate smoothly without significant loss or interference.

It enables high-speed digital and analog signals to reach their intended destinations accurately and reliably. Impedance matching also helps in minimizing electromagnetic interference (EMI) and signal coupling between adjacent traces or components.

Different components and signal traces on a PCB may have different impedance requirements. Therefore, designers carefully calculate and optimize the trace widths, dielectric thickness, and layer stack-up to achieve the desired impedance values.

Specialized techniques like controlled impedance routing and impedance-controlled vias are employed to maintain consistent signal integrity across the PCB.ddddd

Example Problem

How to calculate PCB Impedance?

First, determine the dielectric constant. This should be provided along with the PCB material. For this example, we will use 2.2.

Next, determine the trace width. Measuring the trace width we get a width of 5mm.

Next, determine the trace height/length. This is found to be 10mm.

Next, determine the trace thickness. This is measured to be .5mm.

Finally, calculate the PCB impedance using the formula above.

Z = [ 87 / SQRT(e+1.41) ] * ln [ 5.98H / (.8W +T) ]

= [ 87 / SQRT(2.2+1.41) ] * ln [ 5.98(10) / (.8(5) +(.5)) ]

pcb impedance calculator