Printed Circuit Board Terms

Approximate Surface Roughness
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.