PCB is used for permanent soldered circuits like small scale and large scale electronic accessories and gadgets production in different industries. The marketable circuits or gadgets ae always made with PCBs. An electronic component is an electrical or electronic device such as inductor, resistor, capacitor, and IC etc., that processes the input electrical signal. Each component has a unique symbol that is maintained throughout from schematic drawing to PCB layout. The symbols made for electrical drawing helps to understand and run the board for the team members. The component symbols made for PCB layout and finally printed over the PCB board are helpful during PCB assembly. The symbols made for PCB layout are called component footprints that define to-the-scale shape and soldering point of the component. The component symbols and component footprint may be of same or different shape.
The PCBs have conductive thin copper tracks on one side in single layer PCBs, or on both sides in double layer boards, and on multiple layers embedded within the outermost two layers of the board. The tracks which are generally covered with masked coating propagate signals from one end to the other. Generally, for a single layer, double layer and multilayer PCB, the through hole components are mounted on one side and soldered on the other side of the PCB. The SMT components are mounted and soldered on the same side of PCB. The component density over the multilayer PCBs is much higher as compared to the single and double layer PCBs.
Generally, the components are categorized but not only limited to, following types,
Resistor: general purpose fixed , single or multiturn variable, slider, temperature dependent etc
Switches: Push to ON, Push to off, rotary, toggle, limit etc
Inductor: power supply inductors, high frequency and RF inductors, filter inductors etc
Capacitor: polar and non-polar capacitors, high frequency, power supply etc
Diode: General purpose power supply rectifier type, Zener, schottky, transient voltage suppressor etc
Transistor: NPN and PNP BJT, N-channel and P-channel FETs, UJTs etc
ICs: Analog ICs like operational amplifiers and sensors, digital ICs like gates, microprocessors, comparators, memories, FPGAs and DSPs etc. By PCB perspective each has its unique symbol and pin names for drawing clarity.
Figure 1 shows the different resistor and capacitor footprints, figure 2 shows the 32-pin SMD IC schematic symbol and footprint and figure 3 shows placement of SMD package IC for soldering.
Figure 1: Different sizes and shapes of capacitor and resistor footprints.
Figure 2: IC footprint and schematic symbol
Figure 3: 8-pin SOIC footprint 3D PCB footprint model and soldering on PCB