PCB Design and Layout

A printed circuit board (PCB) holds the parts of a circuit and joins them with copper traces. Designing one is a mixture of electrical rules (how much current, how fast an edge, how much noise), manufacturing rules (what a fabricator can make for a fair price) and judgment (where each part should go so that the whole thing works the first time). This guide takes the subject in ten pages, from the design workflow and layer stack-up through traces, placement, routing, power and decoupling, signal integrity, heat and manufacturing files, ending with three layouts worked through with numbers. Every worked number is computed so that you can check your own board. The circuit design is in Electronics Fundamentals; making and ordering boards is in PCB Prototyping; and putting parts on them is in Soldering.

Start here: what do you need?

I need to…	Go to
plan a board from idea to files, or estimate its size	Design Workflow: Schematic to Board
choose 2, 4 or 6 layers, or hit 50 Ω or 90 Ω impedance	Layer Stack-up and Impedance
size a trace for current, or choose spacing for a voltage	Traces, Current, Spacing and Clearance
decide where each part goes	Component Placement and Floorplanning
route a board, place vias, or avoid split planes	Routing, Vias and Return Paths
distribute power and place decoupling capacitors	Power, Ground and Decoupling
make a fast signal behave, or pass emissions tests	Signal Integrity and EMC
keep a regulator or driver cool	Thermal Design on the Board
send the right files, set rules or review a board	Manufacturing Rules, Files and Design Review
see complete layouts with the numbers	Worked Layouts

A suggested order

Read Design Workflow: Schematic to Board and Layer Stack-up and Impedance first, because they decide everything that follows. Then Traces, Current, Spacing and Clearance, Component Placement and Floorplanning and Routing, Vias and Return Paths are the daily work; Power, Ground and Decoupling and Signal Integrity and EMC make the board work; Thermal Design on the Board and Manufacturing Rules, Files and Design Review make it last and make it buildable; and Worked Layouts pulls it together.

1. Design Workflow: Schematic to Board: The steps from requirements to files, schematic practice, footprints, rules, versions and how big the board will be.
2. Layer Stack-up and Impedance: Two, four and six layer boards, dielectrics, microstrip and stripline impedance, differential pairs and what to ask the fabricator.
3. Traces, Current, Spacing and Clearance: Trace width for current, resistance and voltage drop, fusing, spacing for voltage, creepage and the rules to set.
4. Component Placement and Floorplanning: Zones, connectors, decoupling and crystals, heat, mechanical limits, courtyards and assembly.
5. Routing, Vias and Return Paths: Routing order, vias and their inductance, return current, split planes, stubs and corners.
6. Power, Ground and Decoupling: Power distribution, plane resistance, target impedance, capacitor choice and placement, switching loops and grounding.
7. Signal Integrity and EMC: When a trace is a transmission line, termination, crosstalk, high-speed rules, radiated emissions and ESD.
8. Thermal Design on the Board: Copper area and thermal vias, how hot a part gets, and keeping heat from the parts that dislike it.
9. Manufacturing Rules, Files and Design Review: Fabricator limits, annular rings, mask dams, panels, output files, testing and a design-review checklist.
10. Worked Layouts: Three layouts worked through with numbers: a two-layer sensor board, a buck converter and a four-layer USB board.

Rules of thumb that cover most boards

• Plan the stack-up first. A solid ground plane directly under the signal layer solves half of all noise problems (see Layer Stack-up and Impedance).
• Place before you route. Group by function, put the connectors on the edges and decoupling capacitors beside the pins (see Component Placement and Floorplanning).
• Keep return paths short and unbroken: never route a fast signal over a slot in the plane (see Routing, Vias and Return Paths).
• Size traces for current and temperature rise with IPC-2221, and add margin (see Traces, Current, Spacing and Clearance).
• Design to your fabricator’s rules, not to the minimum a data sheet claims (see Manufacturing Rules, Files and Design Review).
• Review with a checklist before you send the files: a mistake costs a week and a new run of boards.

Quick reference numbers

Topic	Number	Page
Trace width, 2 A, 1 oz external, +10 °C	0.78 mm	Traces, Current, Spacing and Clearance
Copper sheet resistance	0.49 mΩ per square (1 oz)	Traces, Current, Spacing and Clearance
50 Ω microstrip width	2.99 mm on 1.6 mm; 0.35 mm on a 0.21 mm prepreg	Layer Stack-up and Impedance
Spacing at 50 V	0.60 mm external uncoated; 0.10 mm internal	Traces, Current, Spacing and Clearance
Via inductance (1.6 mm board)	1.3 nH	Routing, Vias and Return Paths
Trace inductance	about 1 nH per mm	Power, Ground and Decoupling
Transmission-line length (1 ns edge)	about 25 mm	Signal Integrity and EMC
Thermal via, 0.3 mm in 1.6 mm board	163 K/W each	Thermal Design on the Board
Typical fabricator minimum	0.15 mm trace/space, 0.3 mm drill, 0.15 mm annular ring	Manufacturing Rules, Files and Design Review

Related guides and tools

• PCB Trace Width Calculator: the IPC-2221 width and resistance for your current.
• Electronics Fundamentals and the Design, Testing and Troubleshooting guide: schematic practice and bring-up.
• PCB Prototyping: ordering, cost, lead times and home methods.
• Soldering: pad sizes, stencils and reflow.
• Embedded Systems: the software side of the microcontroller boards you lay out.

FAQ

How many layers do I need?

Two layers suffice for simple, slow boards if you pour ground. Four layers (signal, ground, power, signal) are the sensible choice for microcontrollers with fast peripherals, USB or a lot of pins. See Layer Stack-up and Impedance.

How wide should a trace be?

For signals 0.15 to 0.25 mm; for power size it for current with IPC-2221 (about 0.8 mm for 2 A on an outer layer at a 10 °C rise). See Traces, Current, Spacing and Clearance.

Where do decoupling capacitors go?

As close as possible to each supply pin, with the short, wide connection to the pin and a via directly to the ground plane. See Power, Ground and Decoupling.

What files do I send to the fabricator?

Gerber files for each layer, an Excellon drill file and often an IPC-356 netlist; for assembly add a bill of materials and a pick-and-place file. See Manufacturing Rules, Files and Design Review.

Where did the old PCB Design and Layout sections go?

All of them are in this guide with much more depth: the workflow, trace width and current, spacing and vias, fast signals and impedance, layout practice, files to send, first power-up and troubleshooting each have pages of their own.

References

• IPC-2221B, Generic Standard on Printed Board Design; IPC-2152, Standard for Determining Current-Carrying Capacity in Printed Board Design; IPC-2141A, Design Guide for High-Speed Controlled Impedance Circuit Boards.
• Ott, H. W., Electromagnetic Compatibility Engineering, Wiley; Johnson, H. and Graham, M., High-Speed Digital Design: A Handbook of Black Magic, Prentice Hall.
• Bogatin, E., Signal and Power Integrity: Simplified, Prentice Hall; Montrose, M. I., Printed Circuit Board Design Techniques for EMC Compliance, IEEE Press.
• IPC-7351B, Generic Requirements for Surface Mount Design and Land Pattern Standard; IPC-A-600 (acceptability of printed boards).

Last reviewed: November 2026. Formulas are estimates: confirm impedance, current and spacing with your fabricator and the standards that apply to your product.