PCB glossary: the terms you meet when ordering boards
Short, practical definitions of the words used in PCB design and manufacturing, with links to the guides that explain them in detail.
How to use this glossary
The terms are in the order in which you meet them: files, board structure, copper and holes, surface and marking, processes and testing. Each definition is short; the links lead to the full guide.
Files and data
| Term | Meaning |
|---|---|
| Gerber | The standard file format with one file per layer (copper, solder mask, silkscreen, outline); see the Gerber guide |
| Excellon | The file format of the drill data: hole positions and diameters |
| DFM | Design for manufacturing: designing so that the board can be produced reliably; see the DFM checklist |
| Net | A set of pads and traces that are connected electrically |
Board structure
| Term | Meaning |
|---|---|
| Layer | One copper layer of the board; boards have 1, 2, 4 or 6 |
| Stack-up | The order and thickness of copper and insulating layers; see the stack-up guide |
| Core | A rigid insulating layer with copper on both sides |
| Prepreg | Glass fabric soaked in resin, used to bond layers in lamination |
| FR4 | The standard glass-epoxy laminate of printed circuit boards |
| Tg | Glass transition temperature, above which the laminate softens; see FR4 and Tg |
| IMS | Insulated metal substrate: an aluminium board with one copper layer; see aluminium boards |
| Dielectric | The insulating material between copper layers |
Copper and holes
| Term | Meaning |
|---|---|
| Trace | A copper conductor on the board; see trace width and current |
| Pad | The copper area to which a component lead is soldered |
| Via | A plated hole that connects copper layers |
| Plated hole | A hole with copper in the barrel, which connects the layers |
| Non-plated hole | A hole without copper, for example a mounting hole |
| Annular ring | The copper that remains around a drilled hole |
| Thermal via | A via that carries heat from a pad to a plane; see thermal management |
| Castellated hole | A plated hole cut in half at the board edge; see castellated holes |
Surface and marking
| Term | Meaning |
|---|---|
| Solder mask | The coloured protective layer that leaves only the pads open |
| Silkscreen | The printed text and symbols on the board |
| HASL | Hot air solder levelling: a tin coating on the pads; ours is lead-free |
| RoHS | The EU directive restricting hazardous substances; see RoHS compliance |
Processes and testing
| Term | Meaning |
|---|---|
| Panel | Several boards produced and delivered together; see panelization |
| V-cut | A V-shaped groove that lets boards be broken apart along a line |
| AOI | Automated optical inspection of the copper pattern |
| Flying probe | An electrical test with movable probes; see electrical test and AOI |
| IPC | The industry association whose standards define acceptance classes; see IPC classes |
Missing a term? Write to us, and we will add it. To price a board, use the price calculator.
Frequently asked questions
What is the difference between a via and a plated hole?
A via connects copper layers and carries a signal or current. A plated hole with a component lead soldered into it also connects the layers, but its purpose is mounting the component.
What does Tg stand for?
Glass transition temperature: the temperature above which the laminate softens. We offer 135, 150 and 170 °C.
What is a Gerber file?
The standard exchange format for PCB layers: one file for each copper layer, the solder mask, the silkscreen and the board outline, plus a drill file.
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