The equipment used to make a PCB includes machine-driven tools that help a circuit board technician create the board’s structure. These machines line up, heat and bond the inner and outer layers, with insulating material between them. The accuracy of the alignment and bonding between the layers is crucial for proper sturdiness and electrical performance.
The first step in making a PCB is to design it with computer-aided design (CAD) software. These programs allow the PCB designer to use schematics that show how each component is placed and where the traces go. The designer also uses design grids to arrange components and traces in an efficient manner.
After the design process is complete, a printed circuit board must undergo several tests before it is ready to be soldered and assembled. These tests are performed to ensure that the circuit will operate as it is intended and will not short circuit or produce unwanted electrical contact with other stray wires.
Next, the PCB’s copper traces are etched. This chemical process divides the copper into separate conducting lines called tracks or circuit traces, pads for connecting components, and vias to pass connections between layers of copper. The copper traces are then coated with a solder mask to protect them from accidental electrical contact.
Once the etching is complete, a printed circuit board must be cleaned and aligned before it can be drilled. X-rays are used to ensure that the holes are accurately placed and in proper size and location in relation to other layers of the board.
Drilling is performed with solid-coated tungsten carbide drill bits because the materials on the board are abrasive and can damage the metal. The drill bit is then drilled into the board by computer-controlled drilling machines using a drill file or Excellon file that describes the location and size of each hole.
During this step, the designer also adds any other features that are necessary for the PCB to function properly. This could include extra pads for in-circuit testing, a layer of copper that is not etched, or an electromagnetic shielding.
The board is then laid up on a multilayer PCB fabrication machine that helps to line up, heat and bond the layers together with a copper foil layer and insulating material between them. This process is governed by computer-guided machines because the alignment and bonding between the layers must be exact for the board to function as it is designed.
Another important step is to place conductive or through-hole components. These components are then inserted through the holes, sometimes through metal eyelets that make them conductive or through through-hole component leads. The insertion of through-hole components is one of the most common assembly methods, but it can be difficult to do on a multilayer PCB because the connections between layers must be accurate.
After the conductive and through-hole components are placed, the next step is to route all of the circuit traces between the components. The routes are called circuit traces and can be as simple as a line to connect a single pin pad to the next pad. Or they can be as complex as a line that passes through multiple pin pads and other traces to connect them all to an external circuit.