Layout is where schematic intent becomes geometry. The compulsion to route immediately wastes hours; ninety percent of a good board is placement. Place deliberately, route in the right order, and let copper flow where physics wants it.
At a glance: 8 minute guide · part 3 of 10 in the PCB design complete guide track · includes a worked example and a quick-reference table.
Placement before routing
Here is the working theory in one pass. Group by function, place connectors and mechanical parts first, then ICs with their decoupling caps, then passives nearest their ICs. Route length drops automatically; signal paths become traceable; the board "reads".
| Rule | 2-layer hobby | Typical fab limit |
|---|---|---|
| Min track | 0.25 mm | 0.127 mm |
| Min clearance | 0.25 mm | 0.127 mm |
| Via drill | 0.4 mm | 0.2 mm |
| Plane to edge | ≥ 0.3 mm | 0.3 mm |
| Silk over pads | Avoid | Can be printed anyway |
Routing order and layers
Ground planes stay unbroken. Route critical nets first clocks, differential pairs, feedback dividers then power, then everything else. On two layers: signal top, ground bottom as solid as possible; each cut plane adds an antenna.
DRC and manufacturing checks
Design rules encode the fab's limits (track width, clearance, drill). Run DRC continuously, not at the end. Before export, walk the board: every via, every plane connection, every unconnected net. Gerber preview catches what layout view hides.
How to apply this in your build
Work through the sequence below each step assumes the previous one passed. For numbers that need calculating, the linked tools at the end of this guide do the arithmetic instantly.
- Place connectors and controls to the enclosure first
- Group ICs with decoupling caps adjacent
- Route critical nets before power and fill
- Keep one unbroken ground plane
Worked example
Moving a buck regulator's feedback divider two centimetres closer to its controller dropped output ripple visibly the trace had been sampling switching noise from the inductor loop. Run the numbers yourself with the PCB Trace Width and the result should agree to within rounding.
Practical note from the bench. Before any board ships to fab, we run the "finger trace": follow the signal path with a finger across the layout hesitation marks where the schematic and geometry disagree.
Pitfalls that cost real hardware
- Routing before placement settles
- Splitting ground planes under fast signals
- Letting auto-route finish a board no human then reviews
Key takeaways
- Placement before routing the foundation of this guide; revisit it if any measurement here surprises you.
- Routing order and layers the foundation of this guide; revisit it if any measurement here surprises you.
- DRC and manufacturing checks the foundation of this guide; revisit it if any measurement here surprises you.
Who this guide is for
Beginners get a single focused topic instead of a whole textbook chapter. It works as an early stop in the PCB design complete guide path. Intermediate readers use it as a reference the table, the worked example and the mistake list answer the questions that come up mid-build. If you teach, the structure (theory, application, example, failure modes) maps cleanly onto a lab session.
What you need before starting
Nothing exotic: the parts or tools named in the guide, a multimeter. The PCB Trace Width open in a tab. Place connectors and controls to the enclosure first before you begin the guide assumes it and keep the quick-reference table above within sight while you work through the steps.
Quick reference card
| Aspect | Where to find it in this guide |
|---|---|
| Core theory | Placement before routing |
| Application steps | How to apply this in your build |
| Worked numbers | Worked example |
| Failure modes | Pitfalls that cost real hardware |
How this fits the PCB design complete guide track
This guide is one stop in the structured learning path. Start from the PCB design complete guide complete guide for the full map, or continue with ground planes and return paths and KiCad schematic capture. For the arithmetic, open the PCB Trace Width.
Frequently asked questions
How large should decoupling loops be? As small as physically possible cap within a few millimetres of the pin, direct plane via.
Do I need a 4-layer board? When ground integrity, dense signals, or controlled impedance appear the cost gap has narrowed dramatically.
Is there a calculator for this? Yes the PCB Trace Width tool runs the formulas from this guide instantly, client-side, with no signup.
Keep going with this track
- The complete pcb design guide: PCB Design complete guide
- Read next: rf pcb layout: rules for wifi, lora and beyond
- Also in this track: [what is vlsi design?
- Continue with: kicad schematic capture: clean beginnings
- Calculate as you go: PCB trace width calculator · resistor value decoder · SMD code decoder
- Bookmark this page against the day a measurement surprises you. Most readers return to the table and the mistake list first, and that is the correct order.
Working method notes
When a result here disagrees with your expectation, write down both numbers before changing anything. The gap between predicted and measured is where the real engineering lives. It is usually a tolerance, a parasitic or an assumption that was never checked.
Keep a lab notebook entry for every build in this track. The measured values, the deviations from the guide and the reason for each. Six months from now, those notes are worth more than any tutorial. They describe your bench and your components rather than a general case.
Formulas and checks from this guide
Verification checklist for this track: run DRC early and often, verify footprints against the datasheet drawing. Walk the return path of every fast signal before ordering. A five-minute Gerber preview has saved more fab cycles than any other habit.
Bookmark this page against your next build in the track. The checklist above is the same one used across 15 guides in this series.
What the bench taught us
Run DRC continuously, then once more after every final edit. The last small change breaks the most boards.
Two for hobby density, four the moment ground integrity or impedance matters. The cost gap has collapsed.
Extended Application Notes
This section expands the practical application of pcb layout best practices: placement to routing beyond the worked example, into the situations builders actually meet. Component substitution: when the exact specified part is unavailable, the substitution logic follows the governing parameter of this design, not the nominal value, and the verification step after any substitution is to re-measure the one quantity this guide identified as critical. Batch variation: components vary, and the design margins recommended in the sections above absorb that variation; if a second build behaves differently, the difference itself is diagnostic and points to the tolerance that dominated. Environmental limits: temperature, supply variation and ageing each push a real circuit away from its bench behaviour, and the recommended practice is to test the extremes deliberately rather than discover them in the field. These notes exist because the bench taught them, repeatedly, and each one was once a real troubleshooting session that ended in understanding.
Failure Analysis in Depth
The mistakes section above lists the traps; this section explains why each trap exists and how to recognize it early. Routing before placement settles Splitting ground planes under fast signals Letting auto-route finish a board no human then reviews. Each of these failures has a signature that appears in measurement before it appears in smoke: a reading that drifts, a waveform that differs from the prediction, a temperature that climbs faster than the calculation. The discipline this guide teaches is to measure at the first sign, not at the last, and the sections above give the specific instrument and setting for each check. Failure analysis is not pessimism; it is the fastest curriculum in electronics, because a fault understood once is a fault prevented forever.
Pre-Build Checklist
Before powering any build of this design, run the list: every component value verified against the specification above, the critical measurement points identified and accessible, the instrument modes and ranges chosen in advance, the expected values written down beside the bench, and the power source current-limited for first application. The checklist takes two minutes and replaces the most expensive class of beginner error, which is not ignorance but confidence outrunning verification. Builders who adopt the checklist across the guides in this track report first-apply success rates that feel like cheating, but it is not cheating, it is engineering.
What Comes Next
Having worked through this guide, the natural next steps are the adjacent guides in the track index above, each of which assumes exactly the vocabulary this page built. The calculators linked in the tools section verify every number in seconds, and the complete guide at the head of this track maps the entire curriculum. Read once, build once, measure always: that is the method this site teaches and the method every section above followed before publication.
Theory in Practice, Extended
The theory section of pcb layout best practices: placement to routing deserves one more pass with the bench in mind, because knowing a relationship and applying it under constraint are different skills. In application, the relationship is never isolated: it interacts with tolerances, with temperature, with the behaviour of adjacent stages, and with the measurement itself. The extended practice is to take the governing formula from the sections above and stress it, deliberately. Push the input to the edge of its specified range and watch the output follow the prediction, then push past it and watch the prediction break, because the edge of the specification is exactly where the formula stops being the whole story. That boundary, found on the bench rather than in the datasheet, is the real knowledge this guide offers beyond the mathematics.
Component Sourcing and Substitution Notes
Real builds meet real supply chains, and this section addresses the practical reality. The specified components in this guide were chosen for the reasons stated in the design sections, but equivalent parts from reputable manufacturers almost always serve, provided the governing parameters match, not merely the nominal ones. The substitution checklist: match the parameter this guide identified as critical, verify the package and pinout against the physical part before layout, check the datasheet revision for silent changes, and re-run the verification measurement after installation. Avoid unbranded surplus and marketplace components for anything this guide treats as safety-relevant; the failure mode of a counterfeit is not degradation, it is unpredictability, and unpredictability defeats every other design decision in the chain.
Instrumentation for This Design
Every measurement recommended in this guide maps to a specific instrument configuration, and this section consolidates them. Voltage checks: DC range selected before probing, leads verified against a known source, meter burden considered when the node is high impedance. Current checks: circuit broken at the defined point, meter inserted with the correct range and fuse status confirmed first. Waveform checks: probe compensated against the reference before any amplitude claim, ground lead kept short, bandwidth sufficient for the edge rather than the repetition rate. The instrumentation discipline matters more than the instrument class, and a modest instrument used correctly outperforms an expensive one used casually, a claim this site demonstrates throughout its measurement guides.
Documentation Template for This Build
Close the loop the way professional builds do: record the design values from this guide, the as-built values including every substitution, the measured results beside the predicted ones, and the deviation notes that explain every gap. The template is short, a single page, and it converts a successful build into a reference that survives component changes, firmware updates and the passage of months. Every guide on this site was built and documented exactly this way before publication, and the discipline is offered here as part of the curriculum rather than an afterthought. A build that is documented is twice built, once in copper and once in confidence.
The Layout Review That Catches What DRC Cannot
Design rule checks catch geometry; they cannot catch intent. Before sending any board to fab, do this ten-minute self-review with fresh eyes. Trace every switching regulator's current loop with a highlighter on a printout: input cap to switch to inductor to output cap and back, and if that loop is long or crosses layers twice, shrink it before anything else. Highlight every ground return path under sensitive traces: a SPI line routed over a gap in the ground pour is a future EMC failure that no amount of firmware fixes. Look at connector pin 1 markers, mounting hole clearances, and whether the silk says what each connector actually is ("J3" tells the future you nothing; "FAN 12V" tells the truth). Check that every IC has its decoupling capacitor within 2mm of its power pins, not "somewhere nearby." None of these checks exist in the DRC, and together they are the difference between a board that works first spin and a board that becomes a debugging story. If you remember only one layout rule, make it this: current flows in loops, and every loop is an antenna. Short loops are quiet loops, and every placement decision on the board is really a loop-area decision in disguise.
Last updated 23 August 2026