Printed Circuit Board Assembly
If you open up electronics products, you will most likely find printed circuit boards. These boards are used to connect internal electronic components by small electrical pathways. In essence, the board electrically and mechanically supports the electronic components through the use of conductive tracks or other features. These tracks are etched from one or several layers of copper. The layers are then laminated onto and/or between the sheet layers of the non-conductive substrate. The components are soldered onto the PCB so that they are electrically and mechanically attached.
Printed circuit boards are used in almost all electronic products and in some electrical products. PCBs can be single-layer for simple electronic devices or multi-layer for complex electronic hardware, such as computer motherboards or smartphones, which have as many as 20 layers. PCBs are usually green in color, but they may come in other colors as well.
PCBs may be manufactured as single-sided with a single copper layer, double-sided with two layers of copper on the two sides of the substrate layer, or multi-layer with both outer and inner copper layers and alternating substrate layers. The multi-layer PCBs have a higher component density to allow circuit traces on the inner layers that would otherwise take up surface space between components. The adoption of surface mount technology (SMT) gave rise to the popularity of multilayer PCBs with more than two or four copper planes. The drawback of multi-layer PCBs lies in the difficulty of making a repair, analysis, and field modification of circuits.
The common methods of printed circuit board assembly are through-hole and surface mount technology.
- Through-hole (or thru-hole) technology is the mounting scheme used for electronic components involving the use of leads on the components. These leads are inserted into the holes drilled in the PCB. They are then soldered to the pads on the opposite side by either manual assembly or hand placement or through the use of automated insertion-mount machines.
- Surface mount technology is the method that produces electronic circuits with components that are mounted directly onto the surface of the PCBs. Surface mount technology has eclipsed the popularity of through-hole technology as the favored method of circuit board assembly.
Both through-hole and surface mount technology can be used on the same circuit board. Though surface mount is more popular, through-hole is still preferable for certain components. For example, parts that need very strong physical connections, high heat tolerance, and high power-handling capacity still rely on through-hole technology.