Printed Circuit Boards
A printed circuit board (PCB) has all of its wiring 'printed' onto a board. It does away with most of the hard wiring. The board is made of insulating materials and the wiring is made of a conductive material known as tracks or traces. Suitable slots are made to fit processors, oscillators and other small electronic components. Extremely complex circuits can be printed into a PCB. Printed circuit boards can prove to be very cost effective in mass production because the process is fully automated and the number of defects is quite low. Printed circuit boards are also known as printed wiring boards (PWB) and etched wiring boards.
Copper plating is done on the insulating board and the required wiring is obtained by removing the unwanted copper. Some PCBs are made by adding traces to the bare substrate usually by a complex method of multiple electroplating. Some PCBs have trace layers inside of the the PCB. These devices are called multi layer PCBs. These units are made by bonding together separately etched thin boards. After the circuit board has been manufactured, components are connected to the traces by soldering them to the board.
The three common methods used in PCB manufacture are:
- Silk screen printing, in which etch-resistant inks are used to protect the copper foil. Further etching will remove any unwanted copper. Another method is where the ink may be conductive and printed on a blank (non-conductive) circuit board. This method is also used in the manufacture of hybrid circuits.
- Photoengraving, in which the use of a photomask and chemical etching is used to remove the copper foil from the substrate. The photomask is generally prepared with a photoplotter from data that is produced by a technician using computer-aided PCB design software. Laser-printed transparencies can sometimes be used for low-resolution photoplots.
- PCB milling, in which the use of a 2 or 3 axis mechanical milling system is used to mill away the copper foil from the substrate. A PCB milling machine is often referred to as a 'PCB prototyper'. This machine works quite the same as a plotter as it receives commands from the host software which controls the position of the milling head in the x, y, and (if relevant) z axis. The data which drives the prototyper is taken from files generated in PCB design software and stored in HPGL or Gerber file format.
PCBs are very dependable and inexpensive and even though they need more layout effort and have a higher initial cost than wire-wrapped or point-to-point constructed equipment, they are cheaper, faster, and more consistent in high volume production. PCBs are commonly used around the world in electrical and electronic circuits for computers, consumer and white goods, electrical machinery and automobiles, etc.