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Creating a Schematic
The Schematic-to-Board Workflow
PCB design in KiCad follows a defined sequence: schematic capture, footprint assignment, board layout, Gerber export, and fabrication and assembly. Each stage has a distinct purpose, and skipping ahead creates problems that are painful to fix later. The schematic is always the starting point - it is the authoritative record of how your circuit is connected. The PCB layout is a consequence of the schematic, not the other way around.
Use net labels to decouple sections of the circuit rather than drawing wires all the way across the sheet. A net label is a named connection: any two pins carrying the same label are electrically connected regardless of their position on the schematic. This keeps complex schematics readable and makes functional block labelling practical. Organise your schematic into clear blocks - power supply, signal generation, output - so anyone reading it can follow the intent immediately.
Once the schematic is complete, run the electrical rules check (ERC) before moving on. Fix errors rather than suppressing them. Unconnected pins and missing power flags are the most common sources of ERC warnings, and both are quick to resolve.
Symbols vs. Footprints
A schematic symbol is an abstract representation of a component - it shows pins and their functions, nothing more. A footprint is the physical land pattern manufactured onto the PCB: copper pads, courtyard boundary, and silkscreen outline that correspond to a specific package.
One symbol can map to many footprints. A generic NPN transistor symbol can be assigned a through-hole TO-92 footprint for a prototype or an SOT-23 surface-mount footprint for a production board. This separation lets you finalise circuit topology in the schematic before committing to a physical package.
Footprint Assignment
Footprint Assignment
The footprint assignment step bridges schematic and board: you work through the component list and associate each symbol with a specific footprint from the library. For this course the component mix includes both through-hole and surface-mount parts - resistors, capacitors, the potentiometer, diodes, pin headers, screw terminals, and the voltage regulator. Each footprint reflects real package dimensions, so the manufactured board matches the physical parts you order.
Through-Hole vs. Surface-Mount Components
Through-hole (THT) components have leads that pass through drilled holes in the PCB and are soldered on the opposite side. They are mechanically robust and straightforward to hand-solder, which makes them a good choice for connectors, larger passives, and anything subject to mechanical stress.
Surface-mount (SMT) components sit on pads on the board surface with no through-holes. They are smaller, cheaper at volume, and can be machine-assembled automatically. Hand-soldering SMT requires more care, especially for small passive packages like 0402 or 0603, or fine-pitch ICs. The SMT components in this course are in common packages and are manageable with a standard soldering iron, fine-tipped or chisel, and flux.
Know the scale. A 0402 resistor is approximately 1 mm long and pretty horrible to assemble by hand; 0603 is about 1.6 mm and about the smallest to hand assemble for most people comfortably. Handling them with tweezers and soldering one pad at a time under good lighting is a learnable skill, but it is not the same as soldering a through-hole resistor. For more complex boards, consider applying solder paste using a stencil and hot-plate soldering instead - covered in the Advanced Manufacturing section.
Board Layout
Board Layout
The PCB editor receives the schematic's netlist via "Update PCB from Schematic". All footprints appear as an unplaced stack. The layout process from there:
- Board outline - define the board edge on the
Edge.Cutslayer. Add mounting holes if the board needs to be fastened to an enclosure or chassis. - Component placement - arrange footprints in functional blocks that reflect the schematic structure. Keeping related components close together shortens traces and makes the board easier to debug. Arrange your parts to minimise the number of overlapping ratsnest lines - every overlap saved here makes routing easier.
- Routing - draw copper traces to connect pads according to the ratsnest. Power traces carrying significant current should be wider than signal traces. KiCad's interactive router handles most routing efficiently;
Xstarts a trace andFflips the trace to the other copper layer by placing a via. - Ground and power planes - a copper pour tied to GND is standard practice. It reduces noise, simplifies routing, and provides a low-impedance return path. Fill the GND pour after all other routing is complete. For more complex designs, power/ground planes can really make or break your design and are worth studying in depth on their own.
- Text and labels - add silkscreen labels for test points, connector polarity, and functional callouts. A board that is easy to commission and debug in the field is worth the extra time during layout.
Use high-contrast mode (H) while routing to suppress layers you are not working on. Run the design rules check (DRC) before exporting. Clearance violations and unrouted connections should both be zero before the files leave your machine.
Export & Fabrication
Gerber Export and Fabrication
Gerber files are the industry-standard format for communicating a PCB design to a fabrication house. Each layer - top copper, bottom copper, top silkscreen, top soldermask, board outline - is exported as a separate Gerber file. Drill locations are exported separately as an Excellon drill file.
Before uploading to a fab, open the exported Gerbers in KiCad's built-in Gerber Viewer and check them visually. Verify that the copper, silkscreen, and soldermask layers look correct. This takes two minutes and catches export configuration mistakes before they become a scrapped board order.
If you can, print the board 1:1 on paper and place your physical components on top of their respective footprints. This is a quick sanity check on footprint sizes and board dimensions that costs nothing.
Soldering & Assembly
Soldering and Assembly Order
Solder surface-mount components first, through-hole components second. SMT parts sit flat against pads on the board surface. Soldering through-hole parts first can mean that the bulky packages can make accessing smaller SMT parts tricky. In general, this workflow is best: solder the smallest and lowest-profile parts first, followed by larger ones.
Test as you go. After soldering the power supply section, apply power and verify the output voltage with a multimeter before populating anything else. An unpopulated board is far easier to debug and rework than a fully stuffed one. Repeat staged testing after assembling the signal generation section, and again after the full output circuit is complete.