Circuit boards and schematics

KiCad kicad_pcb kicad_sch, Altium PcbDoc SchDoc PcbLib SchLib PrjPcb, OrCAD dsnolb, Allegro brd dra, Eagle brd sch, CADSTAR cpa csa, PADS, EasyEDA, DipTrace, Fritzing fzz, gEDA, LTspice asc raw, and the files a board travels in: Gerber, Excellon drill, ODB++, IPC-2581, IPC-D-356, IDF and Specctra

A board opens as the board, and a schematic as its sheet: drawn flat, fitted to the pane, the moment you open it. No design program is needed, and nothing is converted first.

Which tool wrote a file, its bytes decide, not its name: a .brd is Eagle's or Allegro's, a .sch Eagle's or gEDA's, a .asc an LTspice schematic, a PADS or a DipTrace export, and each opens as what it is.

What opens

Tool	Files	What is drawn
KiCad	kicad_pcb, kicad_sch	the board, KiCad 4 to 10; the schematic, KiCad 6 on
Altium Designer	PcbDoc SchDoc PcbLib SchLib, PrjPcb	the board, the schematic, the footprints and symbols of a library
OrCAD Capture	dsn, olb, and their backups dbk obk	the design's pages, the library's symbols
Allegro	brd dra, and its text extracts alg fab	the board: tracks, vias, pads, shapes, outline, silkscreen and assembly
Eagle and Fusion 360	brd, sch	the board; the schematic's first sheet
CADSTAR	cpa, csa, the archives its Export > Archive writes	the board; the schematic's first sheet
PADS	the ASCII exports of PADS Layout and PADS Logic (asc, txt)	the board, the schematic
EasyEDA	Standard's json, Pro's epro	the board or the schematic
DipTrace	its ASCII exports (asc)	the board, the schematic
Fritzing	fzz, fz	its breadboard, schematic and board views side by side
gEDA	PCB's pcb, gschem's sch	the board, the schematic
LTspice	a schematic asc; a simulation's results raw	the schematic; the results as signals

What a board travels in	Files	What is drawn
Gerber	gbr ger gtl gbl gto gbo gts gbs gtp gbp gko gm1 pho	one layer, in the colour of what it is (copper, mask, silkscreen)
Excellon drill files	drl xln drd	the holes
ODB++	the job's .tgz or .zip, or its matrix/matrix in the job's folder	the first step, its copper, drill and silkscreen layers stacked
IPC-2581	an .xml whose root is IPC-2581, cvg	the first step
IPC-D-356 netlists	ipc356 d356 356	the test points
IDF	emn (the board), emp (its library, read beside it)	the outline, the holes, each part's outline
Specctra	dsn (a design), ses (a routed session)	the board

ODB++ and IPC-2581 are the two formats a board factory takes in place of a set of Gerbers: one file, or one folder, with every layer, the parts and the nets. IPC-D-356 is the netlist a bare board tester reads. IDF (the Intermediate Data Format) carries a board's outline and its parts' outlines to a mechanical CAD program. Specctra is the autorouter's format, which KiCad and others write for it.

Moving around

The board or sheet opens fitted to the pane. Scroll to pan, and use the zoom bar at the bottom left: − and + step from 25% to 400%, and the percentage between them fits the pane again. + and - zoom from the keyboard, 0 fits.

On a board, the ruler in the toolbar — or M — measures: click a pad, a via, a track or the board's edge, and Shift-click a second for the pitch or the clearance between them; D measures from point to point — see measuring. A schematic has nothing to measure.

Parts, nets and pins

The table mode beside the drawing lists a board's or a schematic's parts, and its parts, nets and pins can be queried with SQL:

Table	A row for	Columns
parts	each part	reference, value, footprint, symbol, side, x, y, rotation, fitted
nets	each net	net, and how many pads, tracks, vias and labels it has
pins	each pin	net, reference, pin

'amp.kicad_pcb' is its parts; 'amp.kicad_pcb!/nets' and 'amp.kicad_pcb!/pins' name the other two:

SELECT net, count(*) AS pins
FROM 'amp.kicad_pcb!/pins'
GROUP BY net
ORDER BY pins DESC

An IDF board adds each part's height. An IPC-D-356 netlist's first table is its test points — net, part, pin, side, position and hole. An Altium project (PrjPcb) opens as the documents it lists, each beside it on disk and opening as itself. Gerber and drill files are drawn only: they hold no parts.

Simulation results

A SPICE results file (raw) — LTspice's, ngspice's, Xyce's or QSPICE's, binary or text — opens as its signals over time, a table for each plot it holds. A camera's .raw is told apart by its bytes.

What is not read

• A KiCad 5 schematic (.sch) and the binary files of Eagle 5 and before are another format: an Eagle file from version 6 on is read, and the app says so by name for the older ones.
• An Allegro board from before 16.0, PADS Layout's own binary .pcb, and DipTrace's binary .dip and .dch are not read; the ASCII exports are.
• A Zuken CR-8000 or CR-5000 design is closed: it says so, and asks for its ODB++ or IPC-2581 export instead.
• ODB++ masks, paste and documents layers are not drawn; an LTspice schematic draws the common symbols built in (resistors, capacitors, coils, sources, diodes, transistors) and any other as a box with its name, since the library is not in the file; a gschem symbol that lives in a library is not drawn, nor a Fritzing part's own picture, which is drawn as the box around its connectors.
• KiCad's footprint and symbol libraries (kicad_mod kicad_sym) open as their text.

Next: 3D models.