PCBs 101

Anatomy of a PCB

Before we get started, lets review what a PCB is. PCB stands for Printed Circuit Board, which is a bit of a misnomer, as the layers of modern PCBs are produced through subtractive processes. Only the silkscreen layers are ever printed - more on that in a second. The term “printed” has its origins in the first PCBs, which were produced by drawing “wires” with conductive ink on an insulating substrate.

PCB Layers

Although the Layer Count, of a board typically refers to the number of copper layers present,

copper layers - used to conduct electric currents. Confusingly, PCBs use ounces as units of thickness for copper layers. This is the thickness of copper achieved if you flatten out an ounce of copper over a square foot of area.
dielectric/prepreg layers - insulating layers which prevent shorts between the copper
solder mask layers - deposited on the top and bottom copper layers, this protects the copper from corrosion and environmental damage, and lends PCBs their color (typically green by default)
silkscreen layers (“silks”) - to call this a “layer” might seem odd, since this is just the text and decals printed on the top and bottom of the board, typically in white ink. Another anachronistic term, most PCB silkscreens are now produced with a direct printing or photoimaging process, rather than true screen printing.

Key PCB Features

Traces (or Tracks) - “wires” etched into the copper layers. Because the copper layers are a predetermined thickness, the width of copper traces is often increased for traces which carry more current. See Step 4 - Route Components for more details.
Vias - holes that go all or partway through a PCB, and which are plated in copper. These allow for signals to travel between copper layers.
Pads - If you’ve made it through the component creation guide, you’ll know that a pad is used to allow a component to be soldered onto the PCB. Pads may be surface mount (flat piece of copper) or through-hole (think an extra wide via).
Copper Pours - wide areas of copper that belong to a single net, so called because it looks like someone “poured” copper over part of the board. These are often used in areas of high current, or when many adjacent components share a common net.

If you’re interested in learning about how PCBs are manufactured, I highly recommend checking out this tour of the JLCPCB factory. Many of the boards on our car likely originated in that very factory!