Designer's Den - PCB Design Information

PCB Design Information.

Here is some useful information for designing general-use printed circuit boards. For other designs and materials, a good source for information is:

Design Standard for Rigid Printed Boards and Rigid Printed Board Assemblies
IPC-D-275
published by the
Institute for Interconnecting and Packaging Electronic Circuits (IPC)
7380 Lincolnwood Avenue
Lincolnwood, IL 60646
[*]PCB Environment
[*]PCB Base Material
[*]Trace Width
[*]Trace Spacing

Environmental Factors

The environment in which a PCB is to be used will change a number of factors needed to design and test it. The ambient temperature is one of these important factors.

Worst Case Environments
CatUSEMin TempMax TempService
1Consumer0°C+60°C1-3 Yrs
2Computer+15°C+60°C~5 Yrs
3Telecomm-40°C+85°C7-20 Yrs
4Civ Aircraft-55°C+95°C~10 Yrs
5Industrial-55°C+55°C~10 Yrs
Auto Pass Cmp-55°C+55°C~10 Yrs
6Mil Gnd/Ship-55°C+95°C~5 Yrs
7Space-40°C+85°C5-20 Yrs
8Mil Aircraft-55°C+95°C~5 Yrs
9Auto Engine-55°C+125°C~5 Yrs
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PCB Base Material

The base material a PCB is made of also affects it's design. Here are some examples materials.

PCB Base Laminate Data
DesignationDielectric
Thickness		Max
Temp
ANSIMIL-P-13949
-PX-105°C
-GE-125°C
FR-4GF.004-.014"120°C
.015 +130°C
FR-5GH.025-.054"140°C
.055 +170°C
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Trace Width Guidelines

Here are some standard trace widths for specific maximum currents. The temperature shown in the table should be subtracted from the delamination temperature for the PCB base material. If the result is negative, the trace is too narrow. For a relatively isolated trace the values may be used directly, but closely spaced traces should be considered as one for temperature calculations. (i.e. an isolated .005" trace carrying 1/2 amp will have a temperature 20°C above ambient. A bus of 10 .005" traces carrying 1/2 amp each will raise the temperature about 30°C) This does not allow for the temperature rise from any parts mounted on the board.

1 Oz. Plating, External Conductors
Width10°C20°C30°C45°C60°C
.005"400 mA500 mA650 mA800 mA1.0 A
.010"800 mA1.0 A 1.3 A1.6 A1.9 A
.015"1.2 A1.5 A1.8 A2.1 A2.8 A
.020"1.5 A1.7 A2.0 A2.5 A3.1 A
.025"1.7 A2.2 A3.0 A3.5 A4.0 A
.050"3.2 A3.9 A4.8 A5.7 A6.5 A
.100"4.8 A6.2 A8.0 A9.5 A10.4 A
.150"6.0 A8.5 A11.0 A12.6 A13.5 A
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1 Oz. Plating, Internal Conductors
Width10°C20°C30°C45°C
.005"200 mA225 mA250 mA275 mA
.010"400 mA450 mA600 mA750 mA
.015"550 mA600 mA750 mA 1.0 A
.020"650 mA700 mA800 mA 1.2 A
.025"750 mA 1.0 A 1.2 A 1.7 A
.050" 1.5 A 1.7 A 2.2 A 2.8 A
.100" 2.2 A 3.1 A 3.7 A 4.5 A
.150" 3.0 A 4.0 A 5.2 A 6.1 A
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Trace Spacing Guidelines

Conductor Spacing
Voltage Between Conductors (VDC or Peak)Minimum Spacing (inches)
Bare BoardAssembly
B1B2B3B4A5A6A7
0 thru 15.004.025.025.005.005.005.005
16 thru 30.004.025.025.005.005.010.005
31 thru 50.004.025.025.005.005.015.005
51 thru 100.004.025.060.005.005.020.005
101 thru 150.008.025.125.015.015.030.015
151 thru 170.008.050.125.015.015.030.015
171 thru 250.008.050.250.015.015.030.015
251 thru 300.008.050.500.015.015.030.015
301 thru 500.010.100.500.030.030.060.030
More than 500.0001 /Volt.0002 /Volt.001 /Volt.00012 /Volt.00012 /Volt.00012 /Volt.00012 /Volt
B1 - Internal Conductors
B2 - External Conductors, uncoated, sea level to 10,000 ft.
B3 - External Conductors, uncoated, over 10,000 ft.
B4 - External Conductors, with permanent polymer coating (soldermask).
A5 - External Conductors, with conformal coating over assembly.
A6 - External Component lead/termination, uncoated.
A7 - External Component lead/termination, with conformal coating.
NOTE: This information is provided as a guideline only. All efforts have been made to ensure it is correct, but it is the responsibility of the user to verify the data is correct for their application.
Page Design by George Patrick (gpatrick@aracnet.com) Last Modified: 12JUL96