Discussion in "Electronics" started by    Ûž TPS Ûž    Dec 10, 2007.
Mon Dec 10 2007, 10:40 pm
#1
PCB Fabrication Process Details

The first step is to transfer the schematic into layout by using PCB designing software such as circuit maker, EAGLE PCB etc. When the layout is done, the board layers are printed onto special toner transfer paper with a laser printer. This board "image" is transferred to the bare copper board with a laminating machine, or a hot clothes iron after laminating, the board with the paper stuck to it is soaked to remove the paper, leaving only the toner behind. The PCB must be cut according to the size of the circuit to make.
Also, it is mainly related with the size of the equipment to incorporate the PCB into. The raw copper board with toner remaining, after the transfer paper has been soaked off. Inside the etch tank, two aquarium pumps circulate etchan (ferric chloride Fe2Cl3) over the copper boards while two aquarium heaters keep the solution at 60 degree temperature. This process can take anywhere from 10-30 minutes depending on the freshness of the solution and thickness of the copper After etching, the toner is removed with solvent and the board is tinned using a soldering iron and a small piece of tinned solder wick. Tinning isn't absolutely necessary but it improves the appearance of the board, and prevents the copper from oxidizing before it's time to solder the parts to the board. At this point, holes are drilled for any leaded components and mounting holes.

Other Process

It uses the mask pattern to prevent that the copper foil in the wiring part of the PCB dissolves in the etchant.The mask pattern can be pictured in the oily dry ink and so on, too. In the introduction this time, we use printed mask pattern for the transparent film

Fixation of the mask pattern
Make the sensitizer surface of the positive exposure printed board the upward and pile the film of the mask pattern on it. Adjust the position of the mask pattern carefully and fix it with the glass of the clamp equipment while careful so as not for the mask to shift
Print of the mask pattern
Print the mask pattern using the fluorescence light.Set the clamp equipment which set the printed board, the mask under the fluorescence light. The ultraviolet rays in the sun are very strong and in the case in the daytime, the exposure completes as much as the 2 minutes. The ultraviolet rays of the fluorescence light are weak. About 20 minutes are necessary to expose. When the exposing time is short, the long development time is necessary.

Development of the sensitizer

Put the board that the print of the mask pattern was ended in the developer of the sensitizer and it removes the unnecessary sensitizer. The part which the ultraviolet rays lashed dissolves in the developer and the copper foil appears. The part which the ultraviolet rays didn't lash doesn't dissolve in the developer and is left as the mask pattern. This mask pattern doesn't dissolve in the etchant .This time, in the development time, it was to be in the about 3 minutes. In the development time, it changes with the size of the printed board, the area which dissolves the sensitizer.
Check the mask pattern carefully at this point.When the mask pattern is broken,repair in resist pen.When the pattern contacts next, shave with the cutter knife.

Etching

It dissolves the unnecessary copper foil part with the etchant. The way of my introducing is the way of using the jet stream style etching device. It is OK even if it puts the etchant in the receptacle to use for the development of the photograph. Put the etchant in the etching equipment and set the temperature.
As for the etchant, 40-43 degC are the suitable temperature. Don’t raise more than 45 degC. Measure the temperature with the stick thermometer. Send the air to the liquid tank and stir the etchant To hang the printed board in the etchant, make a 1-mm hole in the one of the corners of the printed board. Pass the titanium wire through the hole and hang it from the top of the liquid tank. The small hole is open to the lid of the liquid tank, too. Adjust in the length of the titanium wire to become the middle of the liquid tank. Hang the printed board into the etchant .Because the etching time depends on the size of the printed board, the quantity of the copper to dissolve, draw up the printed board sometimes and confirm it. The area of the copper to dissolve becomes long in the time when wide. This time, it was to be in the about 8 minutes. Because the copper in the part of the mask has melted when doing the long time etching, it is necessary to confirm briskly. Be careful so as not for there to be an etchant in the others when drawing up the printed board to confirm the etching condition immediately wash the printed board which the etching completed with the water.

Make the holes

Make the holes which pass the lead line of the parts through the printed board.
In case of the electronic parts of the resistors, the capacitors and so on, it uses the drill bit of the 0.6-mm.For the lead line of the case of the high frequency transformer, it uses the 1-mm drill bit.It is easily opened when using the electric mini drill to make a hole of 0.6 mm, 1.0 mm.As for the hole to fasten the printed board to the case and so on, it uses the 3.2-mm drill bit.Make the hole with the appropriate size in the size of each part, the screw kind.The hole to have opened with the drill becomes the condition that the perimeter is sharp(the burr). Use the bit of the a little big drill to remove this.
In case of 0.6 mm, it is 2.5 mm.
In case of 1.0 mm, it is 2.5 mm.
In case of 3.2 mm, it is 6.0 mm.
It is possible to remove if having the bit of the drill with the hand and doing it the 1-twice lightly

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