PCB DESIGNING

A printed circuit box is a sheet of insulating material usually Bakelite. On this sheet small holes are provided for accommodating the different components of the circuit to be assembled. The components are automatically connected with the each other through copper strips embedded within the sheet.

Each circuit has its own PCB but the method of manufacturing is more or less the same. The printed circuit boards consists of an insulating substrates metallic circuit photo chemically formed upon that substrate. Thus PCB provides sufficient mechanical support and necessary electrical connection for an electrical circuit. Inter-connection between components is achieved by means of conductivity paths running on or through the substrate called TRACK. Track meet components to which they are to be connected by means of larger conductor area called a LAND or PAD. The electrical connection between a land components terminal is achieved by means of a solder. So, it means PCB has two main parts:

(1)Track side(2)Components side

PCB has mainly two types (1)Single side PCB (2)Double side PCB

ADVANTAGES

1. Circuit characteristics’ can be maintained without introducing variation in inter-circuit capacitance.

2. Components wiring and assembly can be mechanized by ware soldering.

3. Mass production can be achieved at lower cast.4. The size components assembly can be reduced with corresponding

decreases in weight.5. Inspection time is reduced as probability of error is eliminated.

DISADVANTAGES

1. As the copper strips are very thin they can carry little hence PCB cannot be used For heavy currents, because in that case the strips will be heated and can cause problem.

2. Soldering need precautions as the risk of strips being over heated and destroyed is always there.

3. For big circuits, PCB cannot be used because it cannot carry heavy components the case and size of PCB in that case will be in tolerate.

CHARACTERSTICS OF PCB MATERIAL:-

Characteristics of copper lead laminated depend on the characteristics of resin and filter used in its manufacturing. Their various characteristics are described below:

ELECTRICAL CHARACTERISTICS: The impartial electrical characteristic are:-

Insulation resistance Dielectric strength Dielectric loss Dielectric constant

PHYSICAL CHARACTERSTICS: The impartial characteristics are:

Flexural strength Water absorption Wrap and theist Punchabilty Non inflammability or flame resistant.

SURFACE TREATMENT OF PCB

For protection from harsh environment, surface treatment of PCB is carried out. For the following is done.

1. GREEN MASKING: A mask of some green lacquer is provided on the whole copper tracts except the solder point. This has following advantages:

a) It is no hygroscopic and protects the PCB against moisture and dampness.

b) It is fire retardant.c) It has high working temperature and high insulation resistance.

2. In place of Bakelite, glass or epoxy may be used, it help in the protection of PCB against harsh environment.

3. The copper tract is dipped into the solution of Fe2, CI2, with few drops of HCL.

PRECAUTIONS WHILE SOLDERING A PCB

The copper strips of a PCB are very thin during soldering they may burn away due to over heating therefore the following precaution should be kept in the mind.

1. Erase out the layer of insulation if any from the PCB.2. For the wiring, use a soldering iron of lower voltage. Usually 35W

soldering iron is preferred.3. Do not keep iron on strip for a time more than required.

4. Use little solder so that the risk of short-circulating of the joints with each with tinned wire.

5. If a trip break out do not fill it with solder but joints its two ends with tinned wire

PCB FABRICATION

There are different type of processes are used to fabricate a PCB but in this project we use manual process. The step required for fabricating PCB as follow:-

1. Firstly a piece of copper clad is selected and cut in a size, which is

being required with the help of hacksaw.2. With the help of steel wool rub it on the PCB to avoid an oxidation,

which is due to temperature.3. Draw a PCB layout of circuit on a paper .The trace a layout on the

PCB with the help of carbon paper.4. Then before etching with the help of photo resist material is coated

on the printed layout for removing extra copper from the PCB instead of layout.

5. The etching process is performed by exposing the surface of board to an etch ant solution which dissolve away the exposed copper area there by leaving the desired conductor pattern on the board. By using a solution Ferric Chloride Cupric Chloride Chromatic Acid and Alkaline Ammonia.

6. To remove photo resists material from the PCB we will use Acetone and kerosene oil.

7. After that we check the continuity by using a by using a multi-meter (DIGITAL MULTI-METER)

8. After that continuity process drilling process is started after that we drill out the hole on PCB with the help of hand-drill.

9. After the drilling process, solder the components on PCB by using soldering iron , soldering wire and flux.

Precautions

1. Size of PCB must be accurate.2. Draw PCB layout correctly before tracing3. A layer of photo resist material should be accurate and fine so that

no short cut takes place.4. Be careful when dip the PCB into the etch ant solution.5. Check the continuity carefully.

SOLDERING AND DESOLDERING

For well over 50 years, using basically the some materials and essentially the same procedure, technician have employed soldering as the “TIME THAT KINDS”

In electronics circuits. For a secure electrical and mechanical joints between wires and components, nothing has replaced it, or is lightly to in the foreseeable future, as an electronic technician, you will need to know how to solder and do it well solder a liquid bond.

Solder is an alloy of tin and lead. The idea nature is 63% TIN & 37% dead with exact combination of tin and lead. Result is good. Any movement

of the components being soldered while the soldered while the solder is in the range will result in cold or bad solder joint. In electrical soldering the alloy mixture is usually 60% tin & 40% dead. With this mixture result will become accurate and solder is heated to 370 degree foraminate and molten upon solidifying the solder from rigid, condition bond with the metal to which it has been applying solder must be used with flux. Flux helps the solder alloy flow around the joint being soldered. It also acts as cleaning agent, decontaminating the components lead and oily film.

SOLDER CONNECTION: To solder in electronic project we need solder iron, flux, solder. The purpose of iron is to heat the joint to be fixed which melts the solder frequently and connection takes place. After cleaning the joint to be soldered, flux follows and then four steps complete soldering connections:-

1. With iron apply heat to the connections.2. Apply solder to the heated section.3. Remove the solder after heating the connection.4. Generally soldering is done on the printed circuit board.

DESOLDERING:

Some times components are incorrectly placed or no longer function, circuit changes are required. In such case, desoldering reheating the joint. When the solder reaches a molten state, it is withdrawn, leaving a solder free connection. The three most common ways to withdraw molten solder. Involve the use of desoldering bulb, pump, braid. The desoldering bulb can be used with any soldering iron. The bulb which has heat resistant Teflon tip, is squeezed and then applied directly to reheated solder connection. When the pressure is released, vaccum action sucks the solder up into the bulb. The bulb can be disassembled and emptied at any time.

The desoldering pump is operated with one hand. A spring-leaded piston creates a vacuum that removes molten solder, desoldering braid is loosely woven. Stranded braid of copper wire. A strip of braid of copper wire. A strip of braid is placed over the solder joint and soldering iron placed is also required to eliminate potential shorts caused by solder balls, blobs, bridges further more poor quality connection resulting from fractured overheated or contaminated solder a necessitate desoldering. Desoldering braid is widely employed for desoldering because it can be used in practically any type of equipment.

The techniques for removing solder from OC boards using desoldering braid are simple and straightfortyard .to remove a solder bridge, place the braid first on trace and heat, then on the opposite trace and heat again.

To desolder a connection from a terminal post. It is necessary to distribute heat from soldering iron throughout the connection. Rock the soldering iron back and forth over the braid to gain maximum solder absorption