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Description / Abstract:
This document is intended as a general guide to understanding
the relationship between current, conductor size, and temperature,
and can be used more specifically in the design and evaluation of
copper conductors in printed boards (PBs).
Purpose
The purpose of this document is to provide guidance on
determining the appropriate conductor sizes on the finished PB as a
function of the current carrying capacity required and the
acceptable conductor temperature rise.
Presentation All dimensions and tolerances in
this standard are expressed in hard SI (metric) units and
parenthetical soft imperial (inch) units. Users of this standard
are expected to use metric dimensions.
Interpretation ‘‘Shall,‘‘ the
imperative form of the verb, is used throughout this standard
whenever a requirement is intended to express a provision that is
mandatory. Deviation from a ‘‘shall‘‘ requirement
may be considered if sufficient data is supplied to justify the
exception.
The words ‘‘should'' and ‘‘may'' are used whenever it is
necessary to express non-mandatory provisions.
‘‘Will'' is used to express a declaration of purpose.
To assist the reader, the word ‘‘shall‘‘ is
presented in bold characters.
Definition of Terms The definition of all terms
used herein shall be in accordance with IPC-T-50
and as defined in 1.4.1 through 1.4.13.
Ambient The surrounding environment coming into
contact with the system or component in question.
Base Material The insulating material upon
which a conductive pattern may be formed (The base material may be
rigid or flexible or both. It may be a dielectric or insulated
metal sheet).
Circuitry Layer A layer of PB containing
conductors, including ground and voltage planes.
Conductive Pattern The configuration or design
of the conductive material on a base material. (This includes
conductors, lands, vias, planes, and passive components when these
are an integral part of the PB manufacturing process.)
Conductor Spacing The observable distance
between adjacent edges (not center-to-center spacing) of isolated
conductive patterns in a conductor layer.
Conductor Thickness Thickness of a conductor
including additional metallic coatings but excluding non-conductive
coatings.
Conductor Width The observable width of a
conductor at any point chosen at random on a PB as viewed from
directly above unless otherwise specified.
Convection Heat transfer that occurs at the
interface of a solid and a fluid or gas that is due to their
differences in temperature.
Copper Weight The mass of copper per unit area
for a foil, typically expressed in ounces per square foot or grams
per square centimeter (these units are not equivalent).
Current-Carrying Capacity The
maximum electrical current that can be carried continuously by a
conductor, without causing an objectionable degradation of
electrical or mechanical properties of the product.
Heat Sink Plane A continuous sheet of metal on
or in a PB that functions to dissipate heat away from heat
generating components.
Thermal Conductivity The property of a material
that describes the rate at which heat will be conducted through a
unit area of the material for a given driving force.
Thermal Resistance The resistance of a material
to the passage of thermal energy, usually measured in degrees
°C/W.