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Contents

• Prerequisites
• What is a PCB?
  • Terminology
  • Layers
  • Issues with Imports
  • Tips

Prerequisites

KiCad Schematic Design

KiCad PCB Design

PCB intro

PCBs (printed circuit boards) are a printed out board where components are soldered into and on them. They help create circuits more reliable and smaller owing to how the connections occur with printed copper on a substrate instead of a series of wires that can become entangled and take up considerably more space. They can be thought of as a permanent breadboard.

Basic terminology:

Traces: The copper traces connect various pads in a PCB. They are analogous to wires, connecting the various components and serve the same purpose.

Vias: The holes in a board where through hole components are mounted.

Pads: The copper (and sometimes silver or gold) pads used with Vias and surface mount components. These pads are what the external components touches to make the electrical connection with the rest of the circuit.

Substrate: The layer of nonconductive material that separates the various conductive parts.

Through Hole Components: Components that do need to have holes drilled for them to be used for a PCB, going into the vias.

Surface mount components: Components that do not need to have holes drilled for them to be used for a PCB, just resting on Pads.

Layers

PCBs cannot have direct overlap, which makes most PCBs impossible to design when crossing wires are present in a schematic, at least on a one layer schematic. What this means is that the substrate has two sides, so an additional layer can be used on the other side of the substrate. If more than two layers are needed, additional two layer substrates can be stacked on top of the existing PCB. This is why PCBs are almost always have even numbers of layers. It should be noted that each additional pair of layers added requires an exponentially greater sophisticated manufacturing process, which dramatically increases cost. Whenever possible, the number of layers should be kept as low as possible.

There are several common nodes that can cover an entire layer, with that layer being just a sheet:

1. Ground is almost always given a whole layer just to itself (even in many 2 layer designs).

2. Power is often given a whole layer itself (for 4+ layer designs especially).

3. Analog ground is often given itself it's own layer just for itself (if many analog components are used).

4. All remaining layers are used for signals.

Imports

There are times when your imported files will not be perfect, having pins incorrectly assigned from schematic to footprint or simply missing. In these cases, you will need to modify the symbol (more rarely the footprint) to add the additional needed pins. This can be done by selecting the symbol, right clicking and selecting edit with symbol editor. From there you just need to add the pins with the correct labels and above all else the right pin numbers (essential for communicating to the footprint).

Tips

1. Many "layers"/planes are not true layers. They often just hold information that is not sent to the actual board. For instance, they could be writing describing what component goes where, dimensions etc.
2. It is advisable that you have built in circuit protection on larger PCBs. This circuit protection could include TVS diodes, fuses (or more rarely circuit breakers), bypass capacitors, or for higher voltages a purpose built chip.
3. Try to have a 0.1uF bypass capacitor (between power and ground) near each chip for every ground & power pin pair. This is to filter out the high frequency noise that chips may attract. For instance, an Op-Amp with 1 +5 V power supply pin, 1 -5 V power supply pin and the noninverting pin connected to ground should have 2 bypass capacitors. Have this capacitor be as close to the power pin on that chip as possible.
4. Add Test points at the most important nodes
5. Try to make the PCB realistically small, to save both space and cost.