ProcirelPCB Layout Best Practices: Placement to Routing
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.
1. Place connectors and controls to the enclosure first
2. Cluster ICs with decoupling caps adjacent
3. Route critical nets before power and fill
4. 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](/tutorial/pcb-design-complete-guide) pillar page for the full map, or continue with [ground planes and return paths](/tutorial/ground-planes-return-paths) and [KiCad schematic capture](/tutorial/kicad-schematic-tutorial). For the arithmetic, open the [PCB Trace Width](/tools/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](/tools/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](/tutorial/pcb-design-complete-guide)
– Read next: [rf pcb layout: rules for wifi, lora and beyond](/tutorial/rf-pcb-layout-guide)
– Also in this track: [what is vlsi design?
– Continue with: [kicad schematic capture: clean beginnings](/tutorial/kicad-schematic-tutorial)
– Calculate as you go: [PCB trace width calculator](/tools/pcb-trace-width) · [resistor value decoder](/tools/resistor-color-code) · [SMD code decoder](/tools/smd-resistor-code)
– 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.