Manufacturing process of PCB (Printed Circuit Board)

©2010 Ganti sree rajiv



Have you ever wondered how this Board is Manufactured??????
• A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conducive pathways or tracks. The PCB can also be referred as Printed Wiring Board.
• PCB was invented by Austrian scientist Paul Eisler.
• PCB is highly reliable, inexpensive (but require higher initial cost)
• The standards of the PCB design, assembly and quality control are set by the IPC organization(Institute for interconnecting and packaging electronic circuits)

There are different types of PCB’s:

• Single-sided PCB
• Double-sided PCB
• Multi layered PCB
• Flexible PCB

Step-1: Raw Material
2 raw materials can be used:

Glass epoxy: white color, hard, made from glass powder, acts as insulator

Bakelite: it is decolum material, not that much hard and cannot carry more weight or voltage

Bakelite can be used when manufacturing cheap materials like TV, Radio,etc.

Step-2: Copper Deposition

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  First the raw material is selected(usually glass epoxy) and on it copper is deposited.
• 
  
  Copper is deposited on the insulator(raw material) for conduction.
• 
  
  For double-sided PCB, copper is deposied on both the sides.

 Step-3: Drilling

• After copper is deposited, the sheet is then drilled.
• Drilling is done to place the components

• Usually all components are placed only on one side of PCB.
• If the PCB is used as double-sided, i.e., if the components are placed two sides, then metallization is done on the epoxy, so as to have interconnection from one side to the other.

Step-4: Image processing

• Depending on the application of the board, first the circuit is designed using the PCB editor software.

• After the circuit is designed in the editor, the design is printed on a ‘negative’.

Step-5: Dry film coating

• A dry film(violet color) is now deposited on the PCB copper layer.
• This dry film is sensitive to UV radiation.

Step-6: Exposure to UV
The negative film is now kept on this dry film deposited on PCB and then exposed to UV rays.

 
The UV rays pass through the white lines but not from the black lines from negative. Hence the circuit design is printed on the dry film.
 
 
Step-7: Etching

• Etching is the process of removing unwanted copper.
• Huge tanks are used and in it etchants are poured. Ex: ferric chloride, ammonium etchant, etc.
• The PCB is placed on the convener belt, and the etchant solution is sprayed on the PCB through nozzles.
• These etchants dissolve the copper.
• After this process, only the dry film lines are seen because the remaining copper is completely dissolved by the etchants.
• The dry film lines are now cleaned using some chemicals. Hence the whole design of circuit is available in copper lines.

• In order to protect the lines to get short circuited, a green film layer is deposited according to our design.
• This film acts as an isolator, hence there will be no connection between the copper lines.

step-8: Placing the components

• To place the components on the board, points are required on the board. These are referred to as Pads.
• Another negative is designed and on it pads(component points) are printed.
• Same process from step 5-7 is repeated on the same PCB.

step-9: Solder Coating

• Solder coating is nothing but coating the PCB with soldering flux so as to have conductivity.
• The PCB board is dipped into the soldering flux at 240degrees and then high air pressure is applied to get uniform coating of 13um.
• Thus all the component points(for placing components) and all connections are made with the solder flux for conductivity.
• Flux: It is a mixture of tin:lead in ratio of 60:40

Step-10: Screen Printing

• It is a method of applying text(such as company logo, part numbers or instructions) to the outer surface of the circuit board.
• It is to have easy access to survey during testing.

MULTI-LAYER PCB’s:

• These PCB’s have one layer over other.
• If the component density is more, then we go for multilayer PCB’s to distribute the components.
• PCB universal thickness sizes:1.6mm(98%used), 2.4mm, 3.2mm

Even in multi-layered PCB’s, irrespective of the number of layers, the final thickness of the board should be one of the above mentioned thickness.

Identification of multi-layer PCB:

• To differentiate between the multilayered PCB and ordinary PCB, on one corner of the board, there will be small square boxes printed.
• The number of boxes indicate number of layers.
• For any board, the soldering side is mentioned as “S”, and the components placing side is mentioned as “C”.

Testing of PCB:

• Each circuit board after manufactured, are subjected to Bare Board Test(BBT), where each circuit connection as defined in the netlist is verified as correct on the finished circuit board.
• Computers are used to control the electrical testing by sending small current through each contact point and verify the current detected.
• After testing, if there are no errors, then a BBT logo is sealed on the board.
• Some common errors which occur in manufacturing PCB’s are:

Dry solder(solder between components wasn’t good, or it gets disturbed while it’s
turning solid).

1. Lines cut
2. Lines short

©2010 Ganti sree rajiv