PCB Layout
SIDACtor
Data Book
5 - 14
Teccor Electronics
(972) 580-7777
The minimum width and thickness of conductors on a PCB is determined primarily by
the current-carrying capacity required. This current carrying capacity is limited by the
allowable temperature rise of the etched copper conductor. An adjacent ground or
power layer can significantly reduce this temperature rise. A single ground plane can
generally raise the allowed current by 50 percent. An easy approximation can be
generated by starting with Figure 5-4 to calculate the conductor cross sectional area
required. Once this has been done, Figure 5-5 converts the cross sectional area to the
required conductor width dependent on the copper foil thickness of the trace.
Figure 5-5 Conductor Width vs. Area
Trace Separation
Because Tip and Ring traces are subjected to transient conditions, they should be
routed towards the edge of the PCB away from sensitive areas, and should maintain a
minimum separation of 2.5mm between themselves and other traces. A good rule of
thumb for separation of non-coated top layer traces is to maintain spacing equal to
.010mm per volt.
Grounding
Although often overlooked, grounding is a very important design consideration when
laying out a protection interface circuit. To optimize its effectiveness, several things
should be considered.
The first is that a large copper plane should be provided using a grid pattern for the
ground reference point.
Next, it should be decided if a single point or a multi point grounding scheme is to be
used. A single-point (also called centralized) grounding scheme is used for circuit
dimensions smaller than one-tenth of a wavelength (
λ
= 300,000/F
kHz
) and a multi
point (also called distributed) grounding scheme is used for circuit trace lengths
0
.350
.300
.250
.030
.050
.070
.100
.150
.200
.010
.020
.005
.001
0
1
10
20
100 150
300
400
500
600
700
Conductor Cross-Section Area (sq mils)
5
30 50 70
200
250
C
0
"
7
0
0
0
2
t
o
2
"
4
1
0
0
2
t
o
1
(2oz/ft2 .0028"
(3oz/ft2) .0042"