Printed Circuit Boards

Start here: ten words every newcomer needs

Overheard on the job

Real-sounding lines from the floor, translated into plain English.

• Rat's nest is clean, fan the BGA out with dog bones and keep the diff pairs off that swiss cheese under the connector.

  TranslationPlacement is good enough to start routing: escape the ball grid array with short pad-to-via traces, and route the differential pairs away from the area where via clearances have perforated the reference plane.

• Board house flagged acid traps and slivers in the DFM and wants to add thieving on layer 4.

  TranslationThe fabricator's manufacturability review found acute copper angles and thin copper strips that could cause defects, and asks permission to add dummy copper to even out plating on layer 4.

• Spin it on a three-day quick-turn, ENIG, Class 2, and send the Gerbers with the IPC-356 netlist.

  TranslationOrder the boards with a three-day expedited lead time, nickel-gold finish and standard IPC acceptance, and include the layer files plus the netlist used for electrical test.

• Smoke test passed but the regulator footprint is mirrored, so it's dead-bugged with two bodge wires until the respin.

  TranslationFirst power-up caused no damage, but the regulator's pad pattern is reversed, so the part is glued upside down and hand-wired until a corrected board is made.

• AOI caught tombstoning on the 0402s and X-ray shows voiding under the QFN, fix the stencil before the next run.

  TranslationOptical inspection found small chips standing on end and X-ray found gas pockets under the QFN's thermal pad, both of which point to changing the stencil apertures.

• Those QFNs sat out of the dry pack all week, bake them or they'll popcorn in reflow.

  TranslationThe moisture-sensitive parts have absorbed water, so they must be oven-dried first or the steam will crack their packages during soldering.

• At 13 to 1 aspect ratio the barrels came out thin, and the coupons failed Class 3 plating.

  TranslationThe holes were too deep for their diameter to plate evenly, and the test structures on the panel showed copper thinner than the high-reliability standard allows.

Laminates, prepregs, copper and the layer stackups that set a board's thickness and impedance.

• Copper weightalso copper thickness, oz copper
  Thickness of copper on a board layer, expressed as ounces of copper per square foot.
• Corealso inner layer core, core laminate
  Fully cured laminate with copper on both sides, etched into inner layers and bonded with prepreg into a multilayer.
• Dkalso dielectric constant, Er
  Dielectric constant: how much a board material slows signals and sets trace impedance, relative to vacuum.
• FR-4also FR4, glass-epoxy
  Flame-retardant glass-epoxy laminate grade that is the default base material for rigid circuit boards.
• Laminatealso copper-clad laminate, CCL
  Sheet of reinforced resin, usually clad with copper foil, that rigid printed circuit boards are built from.
• Prepregalso pre-preg, B-stage
  Glass cloth soaked in partly cured resin, used as the bonding layer that glues cores together in a multilayer board.
• Rigid-flexalso rigid flex, flex-rigid
  Board that combines rigid sections and flexible polyimide circuits in one laminated assembly.
• Rogersalso RF laminate, high-frequency laminate
  Shop shorthand for high-frequency PTFE or ceramic-filled laminate, from the name of a major RF materials maker. Shop talk
• Stackupalso layer stack, stack-up
  Ordered arrangement of copper layers, cores and prepregs that makes up a multilayer board, with each thickness.
• Tgalso glass transition temperature
  Glass transition temperature: the point where a board's resin turns from rigid to rubbery and expands much faster.

Through, blind, buried and micro vias, the holes behind them and the limits of drilling and plating.

• Annular ringalso AR, ring
  Ring of pad copper left around a drilled hole, which must stay wide enough after the drill wanders.
• Aspect ratioalso AR, drill aspect ratio
  Ratio of a board's thickness to the diameter of a drilled hole, which limits how well the hole can be plated.
• Back-drillingalso backdrilling, backdrill
  Drilling out the unused stub of a plated through via from the far side so it does not disturb fast signals.
• Blind viaalso blind via hole, BVH
  Via that starts on an outer layer and ends at an inner layer without passing through the whole board.
• Breakoutalso drill breakout, escape routing
  Drilled hole wandering past the edge of its pad, or the routing that escapes signals from a dense part.
• Buried viaalso buried via hole
  Via that connects only inner layers and is completely hidden inside the finished board.
• Dog bonealso dogbone, dog-bone fanout
  Short trace from a surface mount pad to a nearby via, shaped like a cartoon bone, used to fan out parts. Shop talk
• HDIalso high-density interconnect
  High-density interconnect: boards built with microvias, fine lines and sequential lamination for dense parts.
• Microviaalso laser via, uvia
  Very small laser-drilled via, typically 0.15 mm or less across, spanning one thin dielectric layer.
• PTHalso plated through-hole, plated through hole
  Plated through-hole: a drilled hole whose walls are copper-plated to connect every layer it passes through.
• Tentingalso tented via, masked via
  Covering a via with soldermask or film so its hole is sealed over instead of left open.
• Viaalso via hole, plated via
  Plated hole that connects copper on one layer of a board to copper on another.
• Via-in-padalso VIPPO, via in pad
  Via placed directly in a component pad, filled and plated over so solder cannot drain down it.

Footprints, routing, planes and the rules and slang of layout designers.

• Acid trapalso etch trap
  Acute inside angle in copper artwork where etchant can pool and over-etch, a classic DFM flag. Shop talk
• Clearancealso spacing, air gap
  Minimum spacing between copper features of different nets, or between copper and the board edge or holes.
• Copper pouralso pour, flood
  Area of copper flooded in by the CAD tool around traces and pads, usually tied to ground or a power net.
• Differential pairalso diff pair, pair
  Two traces carrying equal and opposite signals, routed tightly together at matched length and impedance.
• DRCalso design rule check, rule check
  Design rule check: automated scan of a layout for spacing, width, drill and connectivity violations.
• Fanoutalso fan-out, BGA fanout
  Short connections that bring each pin of a dense part out to a via so it can be routed on other layers.
• Footprintalso land pattern, decal
  Pattern of copper pads, outline and markings on a board that matches one component package.
• Ground planealso GND plane, ground layer
  Large continuous copper area, usually a whole layer, that serves as ground and as the reference for signals.
• Impedance controlalso controlled impedance, impedance-controlled routing
  Designing and building traces to a target impedance, such as 50 or 100 ohms, within a set tolerance.
• Keepoutalso keep-out, keepout area
  Region of a board where copper, parts, vias or routing are forbidden by a design rule.
• Padalso land, solder pad
  Exposed copper area on a board where a component lead or terminal is soldered.
• Rat's nestalso ratsnest, ratlines
  Tangle of straight unrouted connection lines a layout tool draws between pads that belong to the same net. Shop talk
• Refdesalso reference designator, ref des
  Reference designator: the label such as R12 or U3 that names one part on the schematic, board and BOM. Shop talk
• Sliver
  Very narrow strip of copper or soldermask in the artwork that can peel loose during fabrication. Shop talk
• Swiss cheesealso swiss-cheesed plane
  Designer slang for a plane so riddled with via clearance holes that its copper is barely continuous. Shop talk
• Thermal reliefalso thermal, relief
  Spoked connection between a pad and a copper plane that limits heat flow so the joint can be soldered.
• Tracealso track, conductor
  Copper conductor path etched on a board layer, connecting pads, vias and planes.
• Trombonealso serpentine, meander
  Back-and-forth trace meander added to lengthen a signal so its timing matches the others in its group. Shop talk

The files and words that carry a design from CAD to the factory.

• Aperturealso D-code
  Shape and size used to draw or flash a feature in Gerber data, named for the opening in a photoplotter's aperture wheel.
• Artworkalso layer artwork, art
  Image of each board layer used to make the phototools for fabrication, and by extension the layer data itself.
• BOMalso bill of materials, parts list
  Bill of materials: list of every part on an assembly with designators, values and part numbers.
• Centroid filealso pick-and-place file, XY file
  File listing the X-Y position, rotation and side of every surface mount part for the pick-and-place machine.
• Drill filealso Excellon, NC drill
  Machine file listing the size and position of every hole to be drilled in a board.
• Gerberalso Gerbers, RS-274X
  Standard file format describing each board layer as a 2D image, sent to the fabricator to build the board.
• Netlistalso net list
  List of every electrical connection in a design, naming which pins belong to which net.
• ODB++also ODB
  Structured CAD-to-fabrication data format that packs layers, drills, netlist and part data into one package.
• Spinalso board spin, turn
  To send a board design out to be fabricated; each build round is a spin, as in the first spin. Shop talk

How bare boards are etched, plated, masked, finished, panelized and graded.

• Board housealso fab, fab house
  Shop name for a PCB fabricator, the company that turns design data into bare boards. Shop talk
• Couponalso test coupon
  Small test pattern built on the production panel and measured or sectioned to prove the boards meet spec.
• DFMalso design for manufacturability, design for manufacturing
  Design for manufacturability: checking and adjusting a design so it can be built reliably at sensible cost.
• ENIGalso electroless nickel immersion gold, immersion gold
  Electroless nickel immersion gold: flat surface finish of nickel topped with a very thin layer of gold.
• Etchingalso etch, copper etching
  Chemical removal of unwanted copper from a board, leaving only the protected circuit pattern.
• Gold fingersalso edge fingers, edge contacts
  Hard-gold-plated contacts along a board edge that plug into a slot, as on a memory module.
• HASLalso hot air solder leveling, hot air levelling
  Hot air solder leveling: finish made by dipping a board in molten solder and blowing off the excess.
• IPC classalso performance class, product class
  Reliability class 1, 2 or 3 under IPC standards, setting the acceptance criteria a board is built to.
• Mouse bitesalso mouse bite, breakaway holes
  Rows of small drilled holes across breakaway tabs so boards snap cleanly from a panel, leaving a nibbled edge. Shop talk
• Panelizationalso panelisation, step and repeat
  Arranging several boards on one production panel so they are fabricated and assembled together.
• Platingalso copper plating, electroplating
  Electrochemical deposition of copper or other metals on a board, building hole walls and surface conductors.
• Quick-turnalso quickturn, quick turnaround
  Expedited board fabrication or assembly delivered in days instead of weeks, at a premium price. Shop talk
• Silkscreenalso silk, legend
  Printed ink layer on a board showing reference designators, outlines, polarity marks and logos.
• Soldermaskalso solder mask, solder resist
  Thin polymer coating over a board's copper that leaves pads exposed and keeps solder where it belongs.
• Surface finishalso final finish, PCB finish
  Final coating on exposed copper pads that stops them oxidising and decides how well they solder.
• Tab routingalso tab route, tab-and-route
  Routing out each board in a panel but leaving small tabs that hold it in place until it is broken out.
• Thievingalso copper thieving, copper balancing
  Adding dummy copper patterns to empty areas of a layer so plating and etching come out even across the panel.
• V-scorealso V-groove, scoring
  V-shaped groove cut partway into a panel from both sides so boards snap apart along straight lines.

Putting parts on boards: paste, stencils, placement and soldering.

• Bakealso prebake, dry bake
  To heat bare boards or moisture-sensitive parts in an oven to drive out absorbed water before soldering. Shop talk
• Fiducialalso fid, fiducial mark
  Small bare copper target on a board or panel that machine vision uses to locate it precisely.
• Pick-and-placealso P&P, PnP
  Automated machine that picks surface mount parts from reels and trays and sets them on a pasted board.
• Reflowalso reflow soldering
  Soldering surface mount parts by melting printed solder paste in an oven that follows a set temperature profile.
• SMTalso surface mount, surface mount technology
  Surface mount technology: soldering components onto pads on the board surface instead of through holes.
• Solder pastealso paste, cream solder
  Mix of fine solder powder and flux printed onto pads to hold parts in place and form the joints in reflow.
• Stencilalso solder stencil, paste stencil
  Thin laser-cut metal sheet used to print solder paste onto board pads before parts are placed.
• Stuffalso populate, load
  To load components onto a bare board, by hand or machine; a stuffed board is an assembled one. Shop talk
• Through-holealso THT, through-hole technology
  Mounting method where component leads pass through plated holes and are soldered on the far side.
• Wave solderingalso wave solder, flow soldering
  Soldering through-hole parts by passing the board over a standing wave of molten solder.

Solder and laminate defects and the inspections and tests that catch them.

• AOIalso automated optical inspection
  Automated optical inspection: camera system that checks boards for missing, shifted or badly soldered parts.
• Bed of nailsalso ICT fixture, pogo fixture
  Test fixture with an array of spring-loaded pins that touch every test point on a board at once. Shop talk
• Black padalso nickel hyper-corrosion
  ENIG defect where corroded nickel under the gold produces dark, brittle solder joints that crack off.
• Bow and twistalso warp, warpage
  Warpage of a board, measured as deviation from flat, which upsets assembly and stresses solder joints.
• Bridgingalso solder bridge, bridge
  Solder defect in which solder joins two pads or leads that should be separate, creating a short.
• CAFalso conductive anodic filament
  Conductive anodic filament: copper growth along glass fibers inside a board that shorts holes under voltage.
• Cold jointalso cold solder joint, cold solder
  Solder joint that never got hot enough to flow and wet properly, leaving a dull, grainy and unreliable bond.
• Delaminationalso delam, layer separation
  Separation between layers of a board's laminate or between laminate and copper, usually from heat or moisture.
• Head-in-pillowalso HiP, head-on-pillow
  BGA defect where a solder ball rests in melted paste but never fuses with it, leaving a hidden weak joint.
• Measlingalso measles
  White spots or crosses inside a laminate where glass fibers have parted from the resin at weave crossings.
• Popcorningalso popcorn effect, popcorn cracking
  Cracking of a plastic IC package in reflow when absorbed moisture flashes to steam, sometimes with an audible pop. Shop talk
• Tombstoningalso Manhattan effect, drawbridging
  Defect where a small two-terminal chip stands up on one end during reflow, leaving the other end unsoldered.
• Voidingalso voids, solder voids
  Gas pockets trapped inside solder joints, seen as light spots on X-ray, which weaken them and block heat.
• Whiskeralso tin whisker
  Hair-like crystal of tin that grows spontaneously from a tin-plated surface and can short nearby conductors.
• Wickingalso solder wicking, copper wicking
  Solder or plating chemistry drawn by capillary action where it is not wanted, up a lead, into a via or along glass.

Lab bench slang for bringing up, debugging and patching boards.

• Blue wirealso jumper wire
  Rework jumper wire on a board, named for the blue insulation often used, and the verb for adding one. Shop talk
• Bodge wirealso bodge, jumper
  Wire soldered onto an assembled board to fix a design error by joining points the copper failed to connect. Shop talk
• Bone pilealso bonepile, fail pile
  Stack of failed or rejected boards waiting for diagnosis and repair, or for scrapping. Shop talk
• Bring-upalso board bring-up, bringup
  Methodical first power-up and debugging of a new board, section by section, until everything works. Shop talk
• Dead bugalso dead-bugging, dead-bug style
  Mounting an IC upside down with its legs in the air and wiring straight to the pins, like an insect on its back. Shop talk
• Golden boardalso golden unit, known-good board
  Known-good assembled board kept as the reference for testing, comparing and debugging others. Shop talk
• Hot airalso hot air station, hot air rework
  Hot-air rework station, or the technique of reflowing parts with a focused stream of heated air. Shop talk
• Kaptonalso polyimide tape, kapton tape
  Amber polyimide tape, named for a well-known brand, used to mask and protect board areas from heat. Shop talk
• Respinalso re-spin, next spin
  Another fabrication round of a board, made to fix problems found in the previous version. Shop talk
• Rework
  Removing and replacing parts or fixing joints on an assembled board to correct defects or make changes.
• Smoke testalso power-on test, first power-up
  First power-up of a new board, usually current-limited, to see whether anything overheats or burns. Shop talk
• Tackalso tack solder, tack down
  To solder one or two pins of a part first to hold it in place before soldering the rest. Shop talk
• Wickalso solder wick, desoldering braid
  Braided copper desoldering ribbon that soaks up molten solder, and the verb for using it. Shop talk

Frequently asked questions

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