1. Circuit diagram
2. Components to be mounted
3. Tracing paper and sketch pen
4. Piece of thermocole
5. Copper clad board and carbon paper
6. Hacksaw
7. File
8. Emery paper
9. Hard pencil
10. Hand drill machines
11. Drill bits (1/32)”, (l/8)”
12. Drawing brush –
13. White paint
14. Razor
15. Tray or dish
16. Ferric chloride as etchant
17. Hydrochloric acid as activator
18. Turpentine oil.

Steps to make PCB

Preparing Layout

With the circuit diagram and all the components in hand, draw a complete layout plan on a tracing paper in the same way as an assembled PCB should look like. For this fix the tracing paper on a piece of thermocole and mount the components on the thermocole through the tracing paper. Show position of the components on the tracing paper showing symbol, and then mark the connecting wire (track) with the help of a sketch pen. Now remove components from the thermocole and give a finishing touch to the markings in such a way that all the connecting wires are shown in equal width with their terminals rounded oIE Case should be taken regarding location, shape and size of the components. Avoid overcrowding utilize the available space fully. Keep the supply line on one side and ground line on the other side.

Printing of PCB

The drawing so prepared is to be transferred onto the copper clad laminate. Keep in mind that the components are to be inserted from under side (non-clad side) of the board. for this proceed as follows:

1. Take a PCB laminate sheet and cut a piece of required size by using a hacksaw. Now file the edges of the board carefully.
2. Put the board on a table keeping copper side on the top. Clean the surface from dust, dirt, grease, oil, etc., using an emery paper.
3. Now put a carbon paper on the board with its side lacing copper surface. Over it. put the drawing with its marked side facing the carbon paper and other side on the top. Since the tracing paper is transparent, you can now transfer a carbon print of the drawing (layout) over the copper surface of the board by rolling a hard pencil over the drawing on the transparent side.
4. When a carbon print has been obtained on the board, drill holes in the board at required places using a hand drill machine. A bit 1/32” may be used for components’ leads and 1/8” bit for fastening screws. Sec that no part of the carbon print is erased or wiped out.
5. Now paint the connecting lines (track) with the help of a drawing brush and white paint and allow the board to dry in the open. After the paint has dried, observe the board carefully. Make required touching for any missing connections. Any excess paint should be scratched off with the edge of a razor.

Etching

For etching (removing) copper from unwanted part of the board, proceed as follows: Remember copper is needed on the track and other circuitry (connections) required for the operation of the circuit. All the other copper from the surface of the board is to be removed or etched off:

1. In a dish or tray, take fresh water and mix a few tea spoons of Ferric chloride (or cupric chloride). Now add few drops of Hydrochloric acid in the solution. The Hydrochloric acid is used as a catalyst (activator) to expedite the etching process. How keep the board dipped completely in this solution. Keep it infor about 15 – 25 min. The solution should be regularly stirred. The stirring also increases the etching speed and reduces the etching time.
2. Observe the change of colour of the naked copper surface of the board. The copper except for the painted portion of the board will be completely dissolved in the solution. This can be seen by change of colour of the board as well as of the solution.
3. Wash the board in running tap water.
4. After the PCB has been thoroughly washed in water remove the paint by a soft piece of cloth dipped in a thinner or turpentine oil.

Finishing

After the above processes are carried out, the components can be assembled (mounted) on the board by soldering. A solder mask can also be provided prior to varnish for protection. The PCB in now ready for use, see Figure 1.

Fig. 1: PCB

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Although each circuit has its own PCB, the method of manufacturing is more or less the same. First of all an insulating sheet of proper size is taken. The whole sheet is covered with copper foil. On this foil the circuit lines are drawn and covered with an enamel layer. After the enamel paint is dried up. the sheet is dipped into the solution of Ferric Chloride (Fe₂Cl₃) with few drops of Hydrocliloric acid (HCI). The copper (except the painted portion) is dissolved in the solution. Later on, this paint is cleaned off by petrol, etc. On this copper strip (track), holes are now drilled to accommodate components. Though each circuit has its own PCB, same PCB can be used for different circuits with slight modifications. But generally this is not done and a separate PCB is prepared for individual circuit.

Fig. 1 A Printed Circuit Board

The exact manufacturing technique of PCB is described in the subsequent chapters.

Note: The PCB is also known as Printed Wiring Board. (PWB) or bprinted Board’ or simply  Hence forth, the term “Board” will mean a PCB/PWB. Figure 1. shows a simple PCB.

Surface Treatment of Printed Circuit Board (PCB)

For protection against harsh environment, surface treatment of PCB is carried out as follows:

(1) A mask (covering layer) of sonic green lacquer is provided on the whole path of the current flow (copper track) except the solder points. This is called green masking. This has the following advantages:

• It is non-hygroscopic and protects against moisture and dampness.
• It is fire retardant
• It has high working temperature
• It has high insulating resistance
• By virtue of its use, stray capacitance is reduced
• Voltage handling capacity of the copper track is improved

(2) A superior insulating material (like epoxy) may be used for making a PCB. It also helps in protection of PCB against harsh environment.

(3) Copper for making tracks should be tinned (the process of mixing tin in proper percentage in copper is known as tinning). This prevents formation of copper oxide and provides protection against harsh environment.

(4) The copper track is dipped into solution of ferric chloride (Fe₂Cl₃) with few drops of hydrochloric acid (HCI). It also helps ¡n protecting the PCB against harsh environment.

(5) It is desirable to provide protection for PCB against dish, dust, contamination, humidity and mechanical troubles. The important insulating creatings are epoxy, polyurethanes, silicones, acrylics. Polystyrenes and varnishes. In selecting a coating material, its following characteristics should be considered:

• Efficiency to protect printed wiring insulation
• The effect of humidity and temperature on insulation resistance
• Electrical properties like dielectric constant, Q-Factor, etc.
• Flexibility
• Resistance against cracking
• Ease of application
• Transparency
• The ease by which it can be removed for repair of the boards.

Advantages of Printed Circuit Board (PCB)

Today PCB is the heart of every electronic instrument in entertainment as well as sophisticated fields. The reasons for popularity of PCBs are:

1. PCB provides support for circuit components and interconnects the components electrically.
2. It avoids bulk wiring and reduces weight of interconnection wiring.
3. It is neat way of routing conductors.
4. Location of parts is fixed allowing easy identification and as a result colour coding is climinated.
5. Assembly errors are minimized due to accurate component mounting.
6. It provides high design tiexibility.
7. Complexity, time and cost of testing. checking process and maintenance of electronic equipment are reduced and simplified.
8. The copper strips over the PCB serve the purpose of wires, hence use of lengthy wires is saved.
9. Copper strips tightly fixed over the PCB and components are soldered with these strips. It gives tight connections which otherwise is not possible.
10. Much time is saved in assembling the circuit over PCB as compared to the conventional method.
11. As components are tightly fixed, risk of sort circuiting is minimzed.
12. Use of PCB saves space unlike in a conventional assembly.

Disadvantages of Printed Circuit Board (PCB)

1. Good amount of skill is required for designing and fabrication of PCBs
2. As copper strips are very thin, PCBs cannot be used in circuits requiring heavy currents because in the case the strips will be heated and can cause problems.
3. Soldering needs precaution as there is a risk of strips being overheated and destroyed.
4. PCB cannot be used for very large circuits as it cannot carry heavy components. and also the cost and size of PCB in that case will be unbearable. Now the integrated circuits (I.C.s) are fast replacing the PCBs.

Precautions While Soldering A Printed Circuit Board (PCB)

As discussed above the copper strips of PCB are very thin. During soldering they may burn away due to overheating. Therefore while soldering a PCB, following precautions should be kept in mind:

1. Erase out the layer of insulation if any, from the PCB.
2. For the wiring, use a soldering ¡ron of lower wattage. For PCB soldering do not use an iron of more than 35 W.
3. Do not keep soldering iron on a strip for more than the time required.
4. Use small solder so that risk of short circuiting ofjoints with each other is minimum.
5. If a strip breaks out, do not fill it with solder but join its two ends with a tinned wire.

The post What is Printed Circuit Board (PCB)? Surface Treatment, Advantages & Disadvantages appeared first on ElectricalWorkbook.

The DFM is a new design technique. Actually, it consists of a set of techniques to design a product in such a way that the cost and time to manufacture the product reduces to minimum. For this, interaction between designer and manufacturer at all the stages (starting from the beginning) is essential.

Proper feedback from the manufacturer to the designer about the problems faced by him during manufacturing is also important for a ‘cost effective’ designing.

Block Diagram of Design for Manufacturing (DFM) 

Figure 1 shows the block diagram of the DFM technique.

Advantages of Design for Manufacturing (DFM) Technique

The DFM technology has following advantages:

1. Improved quality and better reliability of the product
2. Reduced time to fabricate the product
3. Few errors
4. Reduced production costs
5. A long life with trouble free service
6. Reduced maintenance costs.

Guidelines For Design for Manufacturing (DFM)

1. The DFM technique is a new approach to PCB designing; and while adopting this technique, the following guidelines will be helpful.
2. PCB layout should be done keeping in mind the size of the laminate sheet available in the concerned industry, so that maximum utilization of the laminate sheet may be possible.
3. Any plated through hole under a surface mounted component should be ‘solder masked’ to avoid any short circuits.
4. Size of pad should be made just equal to the required size, as a bigger size results in ‘bridging, and a smaller size results in the problem of dry solders. The pad size should also match with the leads of the components.
5. Hole diameter for thru’ hole components should also be just sufficient to allow capillary action of the solder. A larger diameter of the hole will increase consumption of the solder and small diameter results in dry solder joints.
6. The variety of components should be minimum, e.g.. an ASIC can replace several small I.Cs which naturally will minimize the cost. Moreover. uniform orientation of all the components on the board also simplifies assembly and testing of the product.
7. Sufficient margin on all sides of the PCB and sufficient spacing between the components also simplify automatic insertion of the components and their soldering.
8. Proper component spacing and their uniform orientation help in minimizing exposure to the ‘wave’ during wave soldering. Moreover, if nitrogen wave soldering is used, problem of excess solder ¡s eliminated.

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