Circuit Boards Manufactured
A printed circuit board (PCB) provides the structural support and electrical connections for a circuit’s components. Its construction involves dozens of steps with specialized equipment. Understanding the process helps designers optimize the design for manufacturing and collaborate effectively with fabrication partners.
The design for a PCB starts as a schematic diagram, which is a symbolic representation of the circuit’s components and how they are connected. The schematic is then converted into a layout, which is a physical representation of the circuit board exact size and shape. The layout also indicates where the components are placed on the board and the conductive pathways, or traces, that connect them.
Once the layout is ready, it’s sent to a fabrication shop for translation into a physical board. The fabricator creates the copper layers and the substrate, a dielectric material that forms the base of the circuit. The conductive paths are then added using a stencil and chemicals.
How Are Circuit Boards Manufactured and What Materials Are Used?
The first layer added is the copper foil, which serves as the conductive pathway for signals to travel. It’s applied to the copper-clad substrate and bonded with heat under pressure. The thickness of this layer can vary, depending on the design specifications. The substrate is then etched to form the desired circuit pattern. The etching process exposes the copper to a chemical solution that can be selectively dissolved. This removes the unneeded copper from the surface. Once the copper is exposed, it’s plated with gold to resist corrosion and ensure good conductivity.
Several different materials are used for the substrates, which are called laminates in the industry. The most common is FR-4, which is glass-reinforced epoxy laminate sheet stock. This is commonly referred to as green FR-4, although it comes in a wide range of colors. Other popular choices include polytetrafluoroethylene (PTFE, or Teflon), phenolic cotton paper, FR-2, FR-3, CEM-1, and CEM-3. The choice of material impacts the insulating characteristics and price of the final product.
After the etching and plating processes are complete, the copper layer is patterned into a series of tracks, pads, and other features that will later receive solder. The copper is then tinned to prevent it from corroding when exposed to high temperatures. The tin coating also helps the solder bond to the copper. Various coatings can be applied to the substrates as well, including organic solderability preservative, immersion silver, immersion tin, electroless nickel electroless palladium immersion gold (ENIG), and direct gold plating.
Once the copper patterns are finished, the laminate is drilled and plated with holes for component interconnections. The layers are then bonded together under heat and pressure to form the finished circuit board.
Once the boards are fabricated, they’re typically broken into individual units called panels. Panels are then soldered to the components that make up the circuit. Depending on the design, the components may be mounted via through-hole or surface-mount technology. Once the solder has cooled and solidified, it holds the components in place permanently and carries the electrical signals.