The first printed circuit board was made-up by Paul Eisler in 1936 as a component of a radio set. In 1943, the United States government started to use the technology on a massive scale to create proximity fuses (bomb detonators) in World War II. Today, PCBs are important components of almost all equipment such as cars, computers, mobile phones, and many more.
In creating a custom printed circuit board, the electronic diagram of the needed circuit is prepared using either computer-aided software or through manual layout using a stencil. Then, the prototype circuit board will be developed using conventional etching methods or through computer aided manufacturing software.
The common materials used today to manufacture circuit boards are Alumina, Bakelite, CEM5, Arlon, Polyimide, Rogers, Ceramic, GeTek, CEM1, Nelco, FR4 and FR4 High-Temperate. The thickness and the size of the board depend on the requirements of the circuit board. Copper is the widely used material to coat the substrate. With photosensitive coating, the diagram of the printed circuit board will be printed. The unnecessary copper is etched out from the board to form traces. This process is referred to as photoengraving.
There are two common techniques used to develop connecting traces. Silk-screen printing employs a special ink that is resistant to etching and used as a covering for areas where the copper traces have to be developed. Meanwhile, PCB milling is a mechanical system where the unnecessary copper is washed away using CNC machining.
When the circuit board is ready with copper traces, the holes will be drilled into the board to mount the electrical parts using lead. In the drilling process, specialized laser drill or Tungsten Carbide could be used. Usually, the holes created are filled with depressed rivets or coated through electroplating, hence forming an electrical connection among the different layers.
The entire board will be coated except the pads and holes with masking materials. The commonly used materials to mask the board are lead solder, immersion gold, lead free solder, wire bondable gold, immersion silver, immersion tin, flash gold, carbon ink, nickel and copper.
The last step in manufacturing a circuit board is screen printing where the text and legend will be printed on the PCB.
Testing the Printed Circuit Board
Before assembling the parts or delivering the PCBs, it is a standard operating procedure to test the board to determine if there are shorts and opens that could affect its function. A PCB is termed as short if there are unnecessary connections, and a PCB is referred as “open” if there are unconnected points that are supposed to be connected. These errors must be rectified before assembling the circuit board. It is crucial to take note that not all PCB manufacturers test the boards before delivery. This is often referred to as an added expense but an integral one to provide a 100% functional PCB before adding the parts.
Assembling the Printed Circuit Board
When the board is ready, parts will be assembled and mounted on the surface according to the circuit diagram. The most common assembly methods used are through-hole construction and surface-mount construction. There are instances when a combination of these two methods is used in assembling the PCB.
Types of PCB
There are three major types of PCBs – single sided board, double sided board, and multi-layered board.
A single sided PCB is the simplest type because there is only one layer of substrate. All electrical components and parts are mounted on one side and the copper substrates on the reverse side. A double sided board, on the other hand, is the most common type of PCB, where the components are mounted to either side of the substrate. Double sided boards with connecting traces on both sides are often used. Finally, multi-layered boards are composed of several layers of substrate divided by insulation.