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Home > Designing the Target Board for Tracing > PCB track impedance |
Use the following formula only for microstrips (track on outer layer over a ground plane):
where:
h
Height above ground plane (inches)
w
Trace
width (inches), and 0.1 < w/h < 2
t
Trace thickness (inches)
Er
Relative permittivity of processor/prepreg, and 1
< Er < 15
The dimensions h
, w
,
and t
are shown in the following figure.
As an example, the following track (in microstrip form) has an impedance of 51.96Ω:
h
0.005 inch height above ground
w
0.007 inch width track
t
0.0014 inch thickness (1 oz. finished weight)
Er
4.5 (FR4 laminate)
As the track width increases, the impedance decreases.