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Printed Circuit Board
pcb DESIGN
Designing of a pcb is a major slip in the production of pcbs. It forms adistinct factor n electronic perfomance and reliability.The productivity of a pcb with assembly and servicability also depends on design.
The lay out should include all the relevant aspects and details of the pcb design while the network might be produced at 1:1 or 2:1 or even 4:1 scale.it is best prepared on a 1:1 scale.
Steps Involved
1. Prepare the required circuit diagram
2. List out the components, their sizes etc.
3. Draft it onto a graph sheet
4. Place all pads and finish thin tracks
5. Put it on the mylor sheet and then on the graph sheet
6. Place parts including screw holes with the help of knife.
7. Fix all the tracks.
8. Keep one component as the key.
Conversion of circuit diagram
1. Cutting lines , Mounting lines are done
2. List all the components their length diameter thickness code names etc.
3. Keep one component as key component
4. Keep key component first and their supporting tools
5. All tracks are straight lines
6. In between ICs no signal lines should be passed
7. Mark the pin number of IC on the lay out for avoiding dislocations
8. The length of the conductor should be as low as possible
9. Place all the components, resistors ,diodes etc. parallel to each other
PCB layout
Lay out approaches
First the board outlines and the connectors are marked on a sheet of paper followed by sketching of the component outlines with connecting point and conductor patterns. The layout as viewed from the component side first, so as to avoid any confusion. The layout is developed in the direction of signal flow as far as possible.
Among the components the larger ones are filled first and the space between is filled with smaller ones. Components, rewiring input, output connections came near the connectors.
All the components are placed in such a manner that desoldering of the component is not is not necessary, if they have to be re placed. While designing the conductors, the minimum spacing requirement for the final network should be known.
Transforming the lay out to copper
The lay out made on the graph sheet should be redrawn on the copper clad using paint or nail polish.
Etching
The final copper pattern is formed by the tray and dry out for in sunlight for an hour.
Etchants
Many factors have to be considered to choose the most suitable etchant system for a PCB process. Some commonly used etchants are FeCl3, Cupric chloride, Chromic acid etc. After etching FeCl3 is washed from the board and cleaned dry. Paint is removed using suitable from the component insertion. Holes are drilled into appropriate position and the components are soldered into PCB carefully
Etching using FeCl3
Practical implementation
Take a copper clad of the required dimensions. Transfer the circuit layout to the copper clad using cotton paper. The layout area should be marked with nail polish. Put the copper clad into FeCl3 solution and warm it. Stage by stage transformation of the copper clad occurs. Warm the solution Intermittently according to the requirement. After about 4 hours etching will be completed. Wash the board using soap solution to remove the remaining of FeCl3 solution. Scrap off the nail polish and drill holes wherever required using appropriate drill bits. PCB is fabricated.
