Introduction to Printed Circuit Boards – PCB’s

It is abbreviated as PCB. An electrical circuit created by laying printing tracks of a conductor such as copper on one or both sides of an insulating board. This concept was invented in 1936 by  Austrian Scientist Pail Eishler.

PCB is the most essential element in the fabrication of electronic equipment. As it is necessary that all electronic components must connected in a proper manner to obtain the predetermined functions. The way of giving connection is called Networking. This networking to a given circuit can be done in two ways.

A general board by connecting components point to point
A general board by connecting components point to point

Hand Writing

The conducting path is provided using wires between component. It was used earlier, where valve components are in use. As these are obosoleted and semiconductor devices are came in to the picture, the hand writing process became impractical.

Printed Circuit Board Technology

The thin lines of copper foils supported on a rigid substrate as well as interconnections to the electronic components. The usage of PCB makes the circuit more uniform, compact and stable.

Advantages of PCB’s

The advantages of PCB’s compared to conventional electronic circuits.

  • These are in small size, efficient in performance.
  • Laborius wiring, taping is avoided
  • Uniformly in wiring, similar orientation of the components is possible.
  • Fault finding is easy.
  • Mass production is possible and it reduces it cost.
  • It has ability to provide physical support between different types of devices.

Types of PCB’s

A printed circuit board is a piece of an insulating material, generally made from epoxy, on which a copper foil is bonded. The required circuit pattern by drawing the circuit followed by a chemical process of eliminate and exposed carbon layer. The process is called Etching.

As the growth of electronics it composes variety of types, sizes, shapes, the concept of board making also faced number of modifications and in various forms.

Single Sided PCB’s

 

The circuit is present only one side of the insulate substrate. The other side is occupied by the components. This kind of PCB is used for simple circuits with wide tolerances.

Board_design2

The single sided PCB’s are mostly used in small electronics where manufacturing costs have to be kept at a minimum. To jump over conductor tracks.

Double Sided PCB’s

This type of PCB’s are preferred when the density of components are more and cannot be accomodated on one side. In this conductor tracks and connecting wires are present on both sides of copper clad. Two types of double sided PCB’s are commonly used such as

  1. Double sided board without inter layer connection
  2. Double sided board with inter layer connection

double_sided

The former type is simply and extended version over single sided PCB, means two side tracks and components are populated. The second variety is really a new revolution in making of PCB’s.

A question may arise that how an electric connection is given to both sides.. To do this drill holes at desirable positions, so that through the hole an electric flow is maintained from one side of PCB to another. After drilling holes the inner surface is plated by a conductive layer. There fore the dielectric barrel is converted intro a conducting barrel. These holes are not used for mounting the components.

Multilayer PCB

It is the extended version over double-sided PCB’s. In PCB fabrication two parameters are very important.. tracks and number of components, it can be solved by number of layers on which tracks are developed. Prepare number of layers with proper tracks in a dielectric material.

Where overall PCB dimensions no.of arrangement of inter connections are not feasible on double sided PCB.

The frequency requirements call for careful control and uniformity of conductor wave impedance with minimum distortion in single propagation.

Boards for Surface mounted Devices SMD’s

The advent of small, compact and light weight components, a technique called surface mounting., came into PCB world. However copper clad boards used for this same is same as used in double sided PCB’s. In surface mounting process, drilling holes for inserting components leads is eliminated. So that pad size can be reduced to a small area lead to high packaging density.

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Once the PCB is prepared, component leads are positioned on the board surface, than inserting through a hole in previous methods, are soldered properly. The solder joints needs to provide the mechanical attachment  of a surface mount component to its PCB in addition to the electrical connections.

Advantages of SMD’s

  • SMD’s increases in component density per unit area.
  • Reduced track width gives improvement of packaging density
  • Components becomes closer to PCB.
  • The leads reduces spurious electrical characteristics such as inductance and capacitance.