Use of Surface Roughness Symbols
The roughness of any surface, except cast surfaces, may be
expressed by the use of symbols and numerical ratings. The finish
mark symbols are used to designate the applicable surface. The
numerical rating indicates the roughness of that surface.
Control of Surface Roughness
The roughness of any surface is determined by design
requirements rather than by production processes: however, over
control will increase the cost of production. Therefore, specify
surface roughness control on drawing only when it is essential to
the appearance or mechanical performance of the product.
Typical Surface Roughness
Chart
Castings: Do not use symbols and
ratings on cast surfaces.
Mill Cleanup and Shear Cuts............250
to 125.
Machining:.001 to .005
Tolerance..........63.0005 to .001 Tolerance........32.0002 to
.0005 Tolerance......16.0000 to .0002 Tolerance........8
Air Gap:
The nonconductive air space between traces, pads, conductive
matter, or any combination thereof.
Analog Circuit:
A circuit comprised mostly of discrete components (i.e.,
resistors, capacitors, transistors) which produces data
represented by physical variables such as voltage, resistance,
rotation, etc.
Annular Ring:
The width of the conductor surrounding a hole through a Printed
Circuit Pad.
Artwork:
An accurately scaled configuration used to produce a Master
Pattern. Generally prepared at an enlarged scale using various
width tapes and special shapes to represent conductors.
AWG:
American Wire Gauge. A method of specifying wire diameter. The
higher the number, the smaller the diameter.
Axial Leads:
Leads coming out of the ends and along the axis of a resistor,
capacitor, or other axial part, rather than out the side.
Bridging:
A condition that generally happens during the wave soldering
operation where excess solder builds up and shorts out the
adjacent conductors.
Bus:
A Heavy trace or conductive metal strip on the Printed Circuit
Board used to distribute voltage, grounds, etc., to smaller
branch traces.
Bypass Capacitor:
A capacitor used for providing a comparatively low impedance A-C
patharound a circuit element.
Conformal Coat:
A coating that is generally sprayed, dipped, or brushed on to
provide the completedPrinted Circuit Board protection from
fungus, moisture and debris.
Connector Tongue:
A protrusion of the Printed Circuit Board edge that is
manufactured to a configuration to mate with a receptacle that
provides electrical and/or mechanical junction between the
Printed Circuit Board and other circuitry.
Digital Circuit:
A circuit comprised of mostly integrated circuits which operates
like a switch(i.e., it is either "ON" or
"OFF").
Discrete Component:
A component which has been fabricated prior to its installation
(i.e., resistors,capacitors, diodes and transistors).
Feed-Thru:
A plated-thru hole in a Printed Circuit Board that is used to
provide electrical connection between a trace on one side of the
Printed Circuit Board to a trace on the other side. Since it is
not used to mount component leads, it is generally a small hole
and pad diameter.
Flow Soldering:
Also called wave soldering. A method of soldering Printed Circuit
Boards by moving them over a flowing wave of molten solder in a
solder bath.
Glass Epoxy:
A material used to fabricate Printed Circuit Boards. The base
material (fiberglass) is impregnated with epoxy filler which then
must have copper laminated to its outer surface to form the
material required to manufacture Printed Circuit Boards.
Grid:
A two-dimensional network consisting of a set of equally spaced
parallel lines superimposed upon another set of equally spaced
parallel lines so that the lines of one set are perpendicular to
the lines of the other.
Ground Plane:
A condition where all unused areas (areas not consumed by traces
or pads) of the Printed Circuit Board are left un-etched and tied
to the ground circuit throughout the board.
Master Pattern:
An accurately scaled pattern which is used to produce the Printed
Circuit within the accuracy specified in the Master Drawing.
Mother Board:
Also called the Back Plane, or Matrix Board. A relatively large
Printed Circuit Board on which modules, connectors, subassemblies
or other Printed Circuit Boards are mounted and interconnections
made by means of traces on the board.
Plating:
A uniform coating of conductive material upon the base metal of
the Printed Circuit Board.
Radial Lead:
A lead extending out the side of a component, rather than from
the end.
Registration:
The alignment of a pad on one side of the Printed Circuit Board
(or layers of a multi-layer board) to its mating pad on the
opposite side.
Tooling Hole:
Also called Fabrication Hole, Pilot Hole, or Manufacturing Hole.
