How to Design a PCB, Step by Step

A PCB is easier to design than to redesign, so spend ten minutes on the boring list: what powers it (USB, battery, 12 V), what runs it (MCU or ICs), what it talks to (USB, I2C, SPI, UART, wireless), what connects to it (every connector and pinout), how big it can be, and where it lives (temperature, vibration, enclosure). This list decides the regulator, the layer count, and half the placement.

Draw the circuit as symbols and nets, and use real parts from the start: a symbol tied to a footprint tied to an orderable manufacturer part number. Generic symbols feel faster and cost you the time back later, twice. Use power symbols and net labels to keep sheets readable, give every IC its decoupling right there in the schematic, and add test points on the rails you will want to probe. When it is drawn, run the electrical rule check and actually resolve what it flags — unconnected pins and conflicting drivers are the classic first-board bugs.

This is the stage AI helps most. In ProtoFlow you can describe the board in plain English and get an editable schematic with real LCSC, DigiKey, or Mouser parts already attached, then edit it like any schematic; KiCad is the reference manual editor and the format ProtoFlow exports to.

Before layout, confirm each part is in stock at the distributor you will use, in the package you drew, at a price you accept, and that its footprint matches the datasheet land pattern — especially for anything you generated or downloaded. If you plan to have the fab assemble the board, prefer parts in their catalog (for JLCPCB, "basic" and stocked "extended" parts). This is also when you simulate the analog bits that matter — regulator behavior, filters, sensor front-ends — with the built-in SPICE in ProtoFlow or ngspice in KiCad.

Choose the layer count (two layers for simple boards; four when you have an MCU with many signals, any RF, or want a solid ground plane under everything), draw the outline with mounting holes, and enter your fabricator's design rules: minimum trace width and spacing, minimum via drill and annular ring, clearance to the board edge. Typical low-cost fabs publish something like 0.127 mm (5 mil) trace/space and 0.3 mm via holes for standard service — but read the fab's capability page and enter their numbers, not a guess. Rules entered now mean DRC will catch you throughout instead of on the last day.

Place by function: the MCU in the middle with its crystal and decoupling right at the pins, the power section together, connectors at the edges where the enclosure needs them, sensors where they must physically be. Keep switching regulators away from analog and RF. Leave room around the antenna if there is one (copper-free on all layers). A good placement routes itself; a bad one cannot be rescued by an autorouter — which is also why AI-assisted placement in ProtoFlow, or a careful hour by hand, pays for itself.

Route power first and wide (use a trace-width calculator for the current), then the sensitive nets short and direct (crystal, high-speed, analog), then everything else. Give the board a solid ground plane and do not cut it under signal traces; every signal needs a return path directly beneath it. Use vias freely on a two-layer board but keep them out of pads and away from the crystal. An autorouter — ProtoFlow has one built in — is fine for the bulk of ordinary signals once power and critical nets are hand-routed; check its work rather than trusting it.

Run design rule check with the fab's numbers and drive it to zero errors. Then finish the silkscreen: reference designators readable and not under parts, polarity marks on diodes and electrolytics, pin 1 on every IC and connector, and the board name and version somewhere visible. Open the 3D view: parts overlapping, connectors facing the wrong way, and a header under a heatsink are all obvious in 3D and invisible in 2D.

Export Gerbers (copper, mask, silk, outline) and the drill file, plus a BOM and pick-and-place file if the fab is assembling. Load the Gerbers into a Gerber viewer before uploading — what the viewer shows is exactly what the fab will make. Order a small quantity first. When boards arrive, power the rails with nothing else populated or connected, measure them, and only then bring up the rest. That order turns a mistake into a note instead of a smoking part.