What is PCB - How many Types of PCB?

The printed circuit board is also called as printed wiring board (PWB) or printed wiring card. Before the advent of printed circuit board (PCB), the electronic circuits were assembled through a labourious proces of point to point wiring. This used to led to frequent failures at wire junction and short circuits when the wire began to age and crack. Then the wire wrapping method was brought in where a wire is comparatively durable and easily changeable over a period of time, electronics moved from vaccum tubes to transistors and integrated circuits. Due to miniaturisation, the size and cost of electronics components come down and the demand of electronics gadgets increased. This drove electronic manufacturers to look for better solution and the printed circuit board are brought in.

The printed circuit board is a platform for placing electronic and electromechanical components and interconnecting them without discrete wires. The PCB consists of printed conducting wire called PCB tracks and component layouts attached to an insulator sheet. This insulator sheet is referred to as substrate. Substrate is usually made up of glass epoxy (fibre glass reinforced epoxy) or pertinax. The normal thickness of substrate is about 1.6mm. However it can be 0.005 in some cases. PCB allows signals and power to be routed between physical devices.

Also read - How to Design PCB Layout? - Guidelines, Advantages and Disadvantages

Types of PCB

Depending on the complexity of connections involved and component density, the PCB tracks may be routed through a single layer or multiple layers. Similarly, the components placement may be either one side (top or bottom) and or on both sides (top and bottom of PCB. According PCB are classified into the following categories.

Single sided PCB :

For simple, less complicated circuits, only one layer, either top or bottom, is used for routing the connections. Such PCBs are known as single sided PCBs. Here all the connections and tracks are present on one side. If the surface mount device (SMDs) are used in circuit assembly the component placement as well as the track creation is done on one side same side. If some components are 'through hole' components and the track routing is done only on one layer, then the 'through hole' components should be placed on apposite side of the PCB layers holding tracks.

Double sided PCB :

A double layer PCB has two layers of copper foil, one on top and the other on bottom. The component placement can also be done on both the sides. Such PCBs are called double side mounting PCB. In case of such PCBs the connection required from one side to the other side for circuit connectivity is obtained through 'plate through hole' (PTH). The PTH are also called via. The PTH/via is a drilled hole which is either electroplated or reveted with small revets. The via may be buried via if the hole is totally filled with conducting material. The other type of via is visible via with a cylindrical hole and plating on both PCB sides. It is advisable to use less via in a board. The cost of getting double sided PCB is more but the assembled circuit will be compact.

Multilayer PCB :

If the circuit connection complexity is very high, the routing of connections is performed using multiple layers. The additional layers called 'inner layers' are added between the top and bottom layers. The number of inner layers may vary from one to 32 depending on circuit comolexity. It is a common practice to allocate seperate layers for ground and power supply. The seperate ground and supply layer reduces the effect the antena loop formation in circuit. All layers of multiplayers PCB are fabricated separately and finally they are stacked and glued together. Hence the final PCB looks like single PCB.