Saturn Solutions Ltd

Circuit Design

The Circuit Diagram or Schematic is a 'map' of the components and inter-connections in its most easily readable form. The diagram is constructed using one of many standard CADComputer Aided Design packages available and it must show exactly the construction of the printed circuit that is designed from it. Therefore the schematic CAD and printed circuit board CAD are linked through a Net ListA netlist describes the connectivity of an electronic design. and changes to one must always be carried out on the other. The circuit diagram will reference each component on the PCBPrinted Circuit Board. and will list pin numbers for each connection. A good circuit diagram will include as much information as possible to help the reader understand the circuit.

The designer will need to take various things into consideration when producing the circuit including:-

1. Component specifications.

2. Compatibility of components. (There may be interaction issues.)

3. Orientation of components to best suit pin outs.

4. Type of package being used i.e. Surface MountA PCB with tag leaded components soldered flush to solder pads. Holes are still required but not for component leads or ConventionalA rigid PCB with wire-leaded components mounted on only one side of the board with all the leads inserted through holes and soldered into position. (Some SM components can have slightly different characteristics to their conventional equivalents.)

5. Availability of components.

Printed Circuit Board Layout

The Printed Circuit Board (PCB) is the body of material to which components are soldered. Components are connected via one or more layers of metal tracks etched onto and passing through the board. The details for the PCB are taken directly from the circuit diagram and are positioned and placed by the designer for the best (and hopefully simplest) result. This layout represents how the circuit will actually look when produced and, although the connections on the PCB will be identical to the circuit diagram, the two may look completely different. This is because the circuit diagram is intended to be 'readable' whilst the PCB layout is intended to be 'functional'. There may be a lot of unfamiliar terms that you come across when talking about PCBs, so we've put them in a glossary of terms later on in this guide.

The finalised CAD layout file (or Gerber file) is sent to a specialist PCB manufacturer for a small batch to be produced and returned a few days later for a prototype assembly run.