Printed Wiring Board Information

External Trace Current Capacity

Copper trace characteristics

The graph shows the temperature rise on the copper traces, not the temperature of the traces.
The temperature shown in the graph needs to be added to the expected ambient temperature the board will exist at.
The data is for a single trace passing a certain amount of current, which might be acceptable for a two-sided card.
However a number of stacked layers each with there own high current traces might generate a hot spot on the board.

Heat Transfer and Thermal Conductivity
Maximum Current on an External CCA Trace
PWB Etched External Copper Current Capacity

The graph above shows the amount of current an External trace on a printed wiring board can handle.
The picture provides the current rating based on trace cross section in square mils, temperature rise and current in amperes.
The first graph shows the rise in temperature of a trace as the current through the trace is increased, up to 35 amps.
In addition the graph also indicates a temperature rise from 10 degrees Centigrade [room temperature] up to 100C for a trace width up to 700 mils.
For example; if the trace width is 100 square mils, that trace can accept between 3.5A and 10 amps depending on the acceptable temperature rise.

The bottom graph shows the weight of the copper vs. conductor width and cross section of the conductor trace.

Key Phrase:
How much current will a trace handle
What is the current rating of a trace
What trace width will handle a certain amount of current.

Internal Trace Capacity, Buried traces on an internal layer of the board
Dictionary of PCB Terms; Technical jargon used with circuit boards.
PWB Production Vendors, Companies producing Printed Circuit Boards

The table provides minimum conductor spacing vs. voltage

Conductor Spacing per MIL-STD-275
Voltage Between Conductors
Minimum Trace Spacing
DC or AC peak volts
Surface Layers Internal Layers
0 - 100v
0.005" 0.004"
101 - 300v
0.015" 0.008"
301 - 500v
0.030" 0.010"

Military Specifications

Related Military Standards;
MIL-PRF-38535E - Integrated Circuits (Microcircuits) Manufacturing
MIL-PRF-31032 - Printed Circuit Board/Printed Wiring Board, General Specification for
MIL-PRF-55110F - Printed Wiring Board, Rigid, General Specification for
MIL-C-46058C - Insulating Compound, Electrical (For Coating Printed Circuit Assemblies)
MIL-C-47175A(MI) - Compound, Polyurethane, for Conformal Coating of Electronic Circuitry
MIL-C-14550B - Copper Plating, (Electro-Deposited)
MIL-I-46058C - Insulating Compound, Electrical (for Coating Printed Circuit Assemblies)
MIL-STD-275E - Printed Wiring for Electronic Equipment
MIL-STD-2118 - Flexible and Rigid-Flex Printed Wiring for Electronic Equipment Design Requirements for
MIL-T-10727C - Tin Plating: Electro-Deposited or Hot-Dipped, for Ferrous and Non-ferrous metals
RoHS - Restriction of Hazardous Substances

When required, in large the trace to take advantage of the copper thermal conductivity.

Graphic of Minimum Annular Ring, What is a Minimum Annular Ring.
Graph of PWB Ground Potential, moving away from a single point ground connection [example].
.... Description of Ground Loops

Larry's Web Page

Electronic Parts and Equipment Distributors Electronic Component Manufacturers OEM Electronic Equipment Manufacturers EDA Software Producers CAD/CAE Software Engineering Standards, EE Publications Interface/Embedded Computer Bus Electronic Engineering Design Data Engineering Reference Information.
DistributorsComponents Equipment Software Standards Buses Design Reference

Modified 2/4/12
Copyright © 1998 - 2016 All rights reserved Larry Davis