PCB Layout Notes

Created By: Hussein Nosair

Source: Polygons Pours & Copper Regions

* A copper pour on a signal layer is a common part of a PCB design.

* Hatched pour is used for ground plains in an analog design.

* Solid pour is used for carrying heavy currents.

* Solid pour is also used for ground plains meant for EMC shielding.

PCB Design Guidelines

Electrical Design Factors

Conductor Capacitance

C = 0.31 a/b + 0.23(1 + k) log10 (1 + 2b/d +2b + b²/d²)

Where
k = Substrate dielectric constant
a = Conductor thickness
b = Width of conductor in inches
d = Distance between conductors in inches

Conductor Resistance

R = 0.000227W

Where
W = Width of conductor

Characteristic Impedance

Zo = R + jwL / G + kwC

Where
Zo = Apparent Z of an infinitely long line in ohms
R = Resistance in ohms
L = Inductance in Henries
G = Conductor per unit length of line in mhos
C = Capacitance in farads

Characteristic Impedance for a Micro Strip

Zo = (h/W) (377 / (Sqrt. e_r) {1 + (2h/PI W)[1 + ln(PI W/h)]}

Where
h = Dielectric thickness
W = Micro Strip width
e_r = Effective dielectric constant of substrate