The A to Z of PCB Design Terms

Think you know everything about PCB design?

Is this article we take you through the A to Z of PCB terms, which covers nearly every single PCB design term you will ever need. Beware… there are over 100 PCB design terms in this article, so if you want a PDF version to read later contact us. 

Acid Trap:

Vee section of laminate where two tracks are joined at an acute angle. In the days of old with dip processing etchent could remain trapped under the resist.

Apertures:

Gerber files consist of instructions to take specific shaped “pens” and draw particular lines or curves with them. The “pens” are called apertures. In the old days, they were actual templates which would be placed in front of a light, the light switched on, and wherever the light passed through the shape, it would be recorded on the film. These days, it’s all done by a sort of high-end laser printer, but the model of an aperture and a path to sweep it along is still used. Most apertures are simple geometric shapes such as circles and squares.

Artwork:

Traditionally 2:1 or larger, master pattern of the board. Originally drawn using Indian ink or laid out using black paper tape. Term now may refer to 1:1 films.

Back Etching:

Chemical removal of substrate beneath a pad, only normally used on flexible circuits.

Backing Board:

Sacrificial sheet of laminate used on the outside of drilling stack to reduce both exit and entry drilling burrs.

Base Laminate:

Insulating substrate out of which boards are made.

BBT Bare Board Testing:

Using a bed of nails to electrically test for open/short circuits.

BGA:

Ball Grid Array.

Blind via:

A blind via is hole that reaches one outer surface, but stops partway through the board (like a blind alley).
Bomb Sights:

Alignment targets used for aligning circuit layers.

Bonding:

Pressing and fixing together of the layers used to make a muli layer PCB.

Bowing:

Name given to a bent circuit.

Bridging:

Unwanted short causing electrical short circuit.

Buried via:

A buried via is an internal hole that doesn’t reach either external surface.
Burnt Plating:

Grainy rough effect caused by using too high a plating current.

B.V.H.

Buried Via’s, a via buried within a multi layer board.

Clearance:

Name for the isolating gaps between pads and tracks.

Component Side:

Side of board onto which components are mounted.

Contact Print:

A direct 1:1 film copy normally made emulsion to emulsion.

Corner Marks:

Extra tracks used to mark the corners of the circuit board.

Coupon:

Small extra section added on to outside edge of board used for destructive testing.

C/R:

Component reference.

Datum Hole:

Master reference hole from which all other dimensions are measured.

Dielectric Constant

Electrical properties of PCB insulator (for RF designs)
Direct Metallisation:

Process used to make the non conductive areas conductive to enable pattern plating of circuit boards.

Drill File:

File generated by CAD systems, used for programming NC drilling machines.

Drill Tape:

Roll of paper with holes punched in it once used for programming NC machines.

Dry Film:

UV sensitive film laminated on and used to transfer circuit pattern onto circuits. Other types can also be used to apply solder resist.

Earth Plane:

Name given to large area of copper. Often used to provide electrical screening and control the characteristic impedance of signal tracks.

Electroless:

Type of solution used to deposit metal by chemical reactions alone. Slow deposition rates only.

Electrolytic:

Type of solution used to plate metals using an electric current.

Emulsion:

Name given to the active and delicate side of photographic film.

Etch-back:

Process where the substrate is chemically cut back inside holes on a multi layer board. It promotes a better connection to the inner layers.

Etch Factor:

The ratio of etch depth to the amount the resist is undercut during etching.

Etching:

Chemical removal of metals.

Extraneous plating:

Plating where you don’t want it, – on solder mask, on bare laminate, etc.

Eyeballing:

Setting up the alignment of the films to the panels by eye.

Flexible:

A board made from flexible material.

Flexi-rigid:

A board made with both flexible and rigid material.

Footprint:

Name given to specially shaped pad custom designed to accommodate surface mount components.

FR2:

Flame retardant phenolic resin laminate with paper reinforcing.

FR3:

Flame retardant epoxy laminate with paper reinforcement.

FR4:

Flame retardant version of the old G10 epoxy laminate with glass fibre reinforcement.

FR5:

High temperature version of FR4 epoxy laminate with glass fibre reinforcement.

Gerber/Photoplot File:

File format used to produce PCB artwork or tooling.

Glass Transition Temperature:

Temperature at which the resin changes state from solid and becomes very flexible.

G10:

Tradition std non flame retardant epoxy laminate, mostly replaced by FR4.

HASL:

Hot air solder levelling, involves coating the conductors with molten solder then blowing off the excess with a hot air knife.

Hot Oil Reflow:

Process where boards are immersed in a hot oil like mixture to fuse electroplated Tin/lead.

Ident:

Another name to describe the component identification layer.

Immersion Tinning

Process by which the copper tracks and pads on a circuit are ‘pre-soldered’ with a layer of tin, aiding in corrosion/oxidation prevention as well as quick component take-up and dry joint reduction.

IMS:

insulated metal substrates.

Jig:

Frame used for holding panels during plating operations.

Laminate:

Base material that a circuit board is made from.

Land:

Name given to the area of metal surrounding a hole.

Landless Hole:

Name for a hole that doesn’t have a pad surrounding it.

Legend:

Component reference, usually screened ink used to identify components on board.

Markers:

Tracks marking outer edge of circuit board. Boards can often have their profile described as cut to markers.

ML:

Multilayer board, circuit board with extra layers of tracks.

Mother Panel:

Name given to a panel with duplicate circuits on it.

Negative:

Film where clear areas would represent tracks or legend on a board.

Organic Coating:

Lacquer like coating applied to the bare circuit board copper to prevent surface oxidisation.

Organic Metal:

Conductive version of an organic coating, usually sold with a Electroless tin top coat.

O.S.P.

Organic solderability preservative

Pad:

Name for the metal annulus on a board around a hole;

Panel Plating:

Where the whole panel is plated with a metal;

Paper:

Term used to describe FR2 phenolic laminate.

Pattern Plating:

Where only the required tracks and pads are plated with a metal;

Peel Strength:

Measure of the adhesion of the copper to the laminate.

Photo-Resist:

Light sensitive resist used to transfer track pattern onto panel.

Pilot Hole:

Either a small hole to ease or guide the path of a larger drill, or can be the Entry and exit holes for routing which include pips.
Plasma Etch:

Process using ionised gas plasma to remove unwanted resin smear from the inside of holes.

Plip:

Name used to describe connection lugs on a routed panel.

Polyester:

Low melting point plastic film used in flexible circuits.

Polyimide:

Higher melting point plastic film used in flexible circuits.

Positive:

Film where black areas would represent tracks or legend on a board.

Power Plane:

Similar to Earth plane but used as a large copper area to connect a power supply rail to the components.

Prepreg:

Thin sheets of epoxy impregnated glass cloth used to bond multi layer board.

PTH:

Plated-Through Holes. [Circuit boards where the tracks on both sides are interconnected using plated holes.]

Reflow:

Heat up the board to melt/fuse the tin-lead covering the tracks.

Registration:

Describes the layer to layer alignment on the circuit board.

Reversal Print:

Film copy with the same polarity as the original but with the emulsion side reversed.

Robber Bars:

Extra areas of metal added outside the board area. Used to reduce the risks of burning during electrolytic plating.

Roller Tinning:

Application of the solder using a roller rotating in small vat of molten solder.

Routing:

Drill like tool used to profile and cut out large holes, and slots.

Roving Probe:

Same as BBT but carried out using only a few test probes which are mechanically moved around the board.

RS-274D

Name given to old style Gerber photo plotter format.

RS-274X

Name for Newer format of Gerber photo plotter language, includes imbedded aperture tables amongst other things.

Scoring:

V cuts made top and bottom to allow individual circuits to be broken out of a mother panel.

Skip plating:

Missing plating where you do want it – on copper pads,etc.

Slivering:

Breaking away of the tin/lead edges when a track has been undercut during etching.

Smear Removal

Chemical removal of the resin smear inside a drilled hole. Failures in this process would result in poor quality hole plating.

SMOBC

Solder Mask Over Bare Copper.

Soda Strawing:

Small pocket air pocket located along a track edge, trapped under the solder resist.

Solder Resist:

Coating applied onto surface to decrease the likely hood of solder bridges during soldering. Or simply used to make circuit boards look more aesthetically pleasing to the eye.

Spotting In:

Touching up to remove flaws from both photographic masters and the printed circuit pattern.

S/R:

Abbreviation for Solder resist.

Teardrop:

Flaring (widening) of the track as it approaches a pad, forming a teardrop shape.

Tooling Hole:

Hole used by board manufacturer both to align track layers and drilling.

Track:

Electrical route, connection linking pads.

Twist:

Another term for a bent board.

Two Pack:

An ink which is epoxy based, with separate catalyst and resin components. Very tough when cured.

Unclad:

Laminate which has been made without any outer layers of copper.

UV Inks:

Inks which are hardened using high intensity ultra violet light.

Via:

Small hole used solely to interconnect tracks on different layers of the circuit.

Wave Soldering

Soldering joints by passing them over a wave/fountain of molten solder.

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