Essential Parts of a Printed Circuit Board

Understanding PCB Components: Traces, Layers, and Functionality

To have a thorough understanding of Printed Circuit Boards (PCBs), it is important to know the various parts that are used to make the boards.

The most obvious starting point is the board itself. It is plastic, reinforced with glass. The next most obvious parts are the lines and pads that connect together. These are made of copper, and are known as ‘traces’. They conduct electricity, allowing electrical charges to be carried through the board. They are similar to wires, but are much finer, and are used to carry the electricity to the end-point (one of the various types of components within the board).

Simple PCBs are single-sided, with one copper layer. These are structured with one side having all the components, while the other side had the traces. Holes are placed through the board for the circuit to be carried from the trace to the component. For many years, all boards were made in a single-sided design. By definition, double-sided PCBs have traces on both sides of the board.

To allow the boards to be more complex and control additional functions, multi-layer boards are used. Additional layers of board have their own set of traces and components. In developing multi-layer boards, a range of issues needed to be addressed. Firstly, it is essential that the copper connections do not cross each other, as this would compromise the path of the electrical circuit. Other factors that need to be considered are resonance and noise and capacitance.

The layer set in place above the copper is called the soldermask. This is a form of insulation, ensuring that the copper traces aren’t affected by any metal that may come into contact with it. It is traditionally colored green. It is designed to have gaps that expose the copper in specific places, providing points where components can be soldered to the board. The silkscreen is a layer that is printed onto the soldermask. It is a layer where text can be printed (letters and numbers) that provide instructions for the user.

A range of components can be incorporated into a PCB. Without components, the PCB is simply a conductor of electricity, with no function. Components can be grouped into two broad categories – passive (components that do not require direction) and active (components that only function when they receive current from one direction). Common components include:

  • Batteries: these provide the circuit with voltage.
  • Capacitators: The store electricity for later use. They are available as polarized or non-polarized.
  • Diodes: allows current to pass in one direction only, blocking the other.
  • Inductor: These coils store charge in a magnetic field.
  • Light emitting diodes (LEDs). These light up when current flows is applied. They only allow current to flow in one direction.
  • Resistors: These control the electric current as it passes through. The level of resistance provided varies based on the needs of the engineer. They are made in different color codes to show the level of resistance.
  • Switches: These can be open or closed, allowingor blocking current.
  • Transistors: These are a form of switch that performs changes function based on the voltage passing through.
  • Vias: small holes in the board that allow a signal to be passed from one side to the other