Notes on Circuit Board Construction and Anatomy

  • First consider the base material
    • Single Layer:
A Single Layer PCB Base Material
A Single Layer PCB Base Material
  • Double Layer:
    • Just add a layer of copper to the single layer
A Two Layer PCB Base Material
A Two Layer PCB Base Material
  • Mutli Layer:
    • Layers are usually in multiples of two, because of the manufacturing method
      • "Core Layer"
        • Much like the double layer board, except it utilizes thinner epoxy glass
        • Double layer boards only have thick epoxy glass for rigidity
      • Core Stackup
A Four Layer PCB containing a PCB Core
A Four Layer PCB containing a PCB Core
  • Dimensions:
    • Manufacturers will specify normal layer thicknesses, but engineers can specify for special cases
    • Thickness is controlled by adding or subtracting epoxy glass layers, or using thinner or thicker copper
      • Note: Reducing epoxy glass thickness will make the board less rigid, and will decrease "volt spacing"

Note: Circuit boards are not limited to 1-4 layers. In fact, some very advanced boards can be up to 100 layers!

  • Traces
    • What is a trace?
      • Essentially, a wire, cut into the copper part of the circuit board
A magnified look of what makes a trace
A magnified look of what makes a trace
  • How are traces made?
    • Based on a design, copper is removed from areas around traces, to make the trace electrically separate (no continuity) from the rest of the copper.
    • Two methods for manufacturing:
      • Milling
        • Using a tiny endmill and a CNC controlled mill, material is cut out according to a sed of G-Code instructions generated from the board design file
      • Chemical Etching
        • A transparent sheet has an image of the board layout printed on it
          • black means: keep material
          • clear means: remove material
        • A reaction with light, the chemical, and the copper trace take place, dissolving the copper in specified regions
A PCB in the process of getting Photo-etched
A PCB in the process of getting Photo-etched
  • Vias and Through-Holes
    • Vias are for connecting traces from layer to layer
A four layer board with a via connection the first and third layer
A four layer board with a via connection the first and third layer
  • Through-holes are very similar to vias, except they end on the bottom layer with "solder pads"
Solder Pads
Solder Pads
  • Electroplating:
    • Using high precision placement and head, copper is plated on the edge of the holes drilled for vias and through-holes
  • Solder Resist:
    • Using a similar method to chemical etching, a photo sensitive reaction adds solder resist where specified
    • Solder resist will not allow molten solder to bond with it
    • It serves two purposes:
      • Preventing Solder Bridges
      • Insulating Traces from the rest of the world
A board with a component lead soldered into a through-hole
A board with a component lead soldered into a through-hole