PCB stands for printed circuit board. It is a thin insulator plate like FR-4 coated with a very good conductor material such as copper that is used to connect different components placed on this board. A component is basic electrical or electronic device such as resistor, capacitor, inductor IC etc., that performs a particular function when supplied an input signal. A device or component is made of some processed natural material and for physical connections the metallic leads are jointed. These leads are soldered over the PCB on copper side. The metallic leads are soldered and connected to each other through thin copper tracks. Solder is an alloy of different metals that is used to make hard connections between the track of the PCB and the component lead. Because this is an alloy it makes possible a strong mechanical as well as electrical connection between PCB and component.
The FR-4 laminated sheet with thin layer of copper makes a skeleton for components placement and soldering. The components which are placed over the PCB are:
Switches: Allows current flow when in ON position otherwise stops current flow
Resistor: controls the current flow when applied the voltage across it
Capacitor: Stores the electric charge with an existence of a potential difference across it
Inductor: Stores magnetic field and opposes flow of current
Diode: Allows passing current in forward direction but stops in the other direction
Transistor: A signal amplifying or switching component
The above mentioned components are very basic building blocks of electronic components. There are many complex devices which are used in thousands of billions every year in different electronics products.
In a circuit board application the components are modeled first for schematics and then for PCB layout. The models for schematics are known as component symbols which show the type of components, number and type of pins and their values. They are made for circuit functionality understanding and easy readability of the drawings. The component models used for PCB layout are the shape and size exactly what the component looks like in the real world. The PCB model of a component s is called a footprint. In the early times the electronic components were modeled what they look in x and y direction i.e. the size in terms of length and width of the component along with their pins position. But now-a-days electronic products are becoming more and more complex the footprint s are made in 3D shape i.e. modelling the length, width and height aspects of a component that show the components’ length, width and height feature on the PCB.
Figure 1 shows the different resistor sizes, figure 2 shows the transistor schematic symbols and different packages and figure 3 shows the 3D footprint of an 8-pin SOIC package IC and its soldering on PCB.
Figure 1: Different sizes and shapes of resistor packages.
Figure 2: Transistor schematic symbol and different packages
Figure 3: 8-pin SOIC footprint 3D PCB footprint model and soldering on PCB