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1
- #1
nbucska
Electrical
- Jun 1, 2000
- 2,191
The basic process : The copper-clad board is covered with
a photosensitive layer (solution or dry film ) which upon
illumination changes the solubility. Developed with a
solvent either the illuminated or the un-illuminated sections remain on the surface and act later as an etching mask.
The copper is usually etched with ferricloride (FeCl2) or sodium persulphate.
The plating the through holes:
After drilling the board is sensitized with Palladium cloride solution. This, when drying, partially dissociates and leaves some metallic palladium on the surface. This acts
initially as catalyser to precipitate copper from a solution
of CuSO4-NaOH-tartaric acid. After the Pd is covered by Cu,
the later catalizes the process.
For amateurs obviously the plated-through holes are too difficult( the process is VERY critical for cleanliness ).
For simple PC boards:
1.) You can buy sensitized copper clad PC boards. You need
a black-white ( hi contrast) negative. It is usual to hold
the negative with vacuum to the PC board but pressing it
-- and the board to a glass plate with a foam works, too.
Use UV or even sunlite for exposition. Follow recipe on package.
You can buy developer, too.
2.) You can buy special paper on which you can XEROX the schematics and you can transfer the picture to the bare board with a hot iron. The resolution of the process is limited, some experimentaion is needed.
3.) Very cheap, low resolution but FAST process:
Beat up the white of one egg ( NO YOLK !!! ) into a hard foam- mix this into one quart of water, shake, let it settle. Filter it through a cellulose sponge or filter paper, add 3 to 6 gram potassium dichromate.
You can store it in the refrigerator for weeks.
Before use, add ammonium hydroxide -- ammonia -- by drops
-- constantly mixing-- until the color changes from orange
to lemonade yellow.
Clean the board from oil, wash with detergent, water. Dip into the solution -- it has to wet the surface uniformly -- and dry it in dark place. The layer is invisibly thin.
Expose with UV or sunlight. The exposed surface will darken.
To develop: With a rubber roller coat the surface uniformly
with a thin layer of OFFSET-ink ( black, sticky, oily stuff..)Soak in cold water -- when the coating starts to lift, wash it off under running water. After drying, spread some powdered Syrian asphalt on it and shake/tilt it until all of the offset ink is covered with it. Pour off the surplus.
Now spread some talcum powder on the surface and wipe it off with a cotton-ball dipped into talcum. The surface is uniformly gray.
In oven, heat the board until the asphalt melts to shiny black.
4.) Special offset printing press can print the board directly -- Coat it with asphalt, etc...
<nbucska@pcperipherals.com>
a photosensitive layer (solution or dry film ) which upon
illumination changes the solubility. Developed with a
solvent either the illuminated or the un-illuminated sections remain on the surface and act later as an etching mask.
The copper is usually etched with ferricloride (FeCl2) or sodium persulphate.
The plating the through holes:
After drilling the board is sensitized with Palladium cloride solution. This, when drying, partially dissociates and leaves some metallic palladium on the surface. This acts
initially as catalyser to precipitate copper from a solution
of CuSO4-NaOH-tartaric acid. After the Pd is covered by Cu,
the later catalizes the process.
For amateurs obviously the plated-through holes are too difficult( the process is VERY critical for cleanliness ).
For simple PC boards:
1.) You can buy sensitized copper clad PC boards. You need
a black-white ( hi contrast) negative. It is usual to hold
the negative with vacuum to the PC board but pressing it
-- and the board to a glass plate with a foam works, too.
Use UV or even sunlite for exposition. Follow recipe on package.
You can buy developer, too.
2.) You can buy special paper on which you can XEROX the schematics and you can transfer the picture to the bare board with a hot iron. The resolution of the process is limited, some experimentaion is needed.
3.) Very cheap, low resolution but FAST process:
Beat up the white of one egg ( NO YOLK !!! ) into a hard foam- mix this into one quart of water, shake, let it settle. Filter it through a cellulose sponge or filter paper, add 3 to 6 gram potassium dichromate.
You can store it in the refrigerator for weeks.
Before use, add ammonium hydroxide -- ammonia -- by drops
-- constantly mixing-- until the color changes from orange
to lemonade yellow.
Clean the board from oil, wash with detergent, water. Dip into the solution -- it has to wet the surface uniformly -- and dry it in dark place. The layer is invisibly thin.
Expose with UV or sunlight. The exposed surface will darken.
To develop: With a rubber roller coat the surface uniformly
with a thin layer of OFFSET-ink ( black, sticky, oily stuff..)Soak in cold water -- when the coating starts to lift, wash it off under running water. After drying, spread some powdered Syrian asphalt on it and shake/tilt it until all of the offset ink is covered with it. Pour off the surplus.
Now spread some talcum powder on the surface and wipe it off with a cotton-ball dipped into talcum. The surface is uniformly gray.
In oven, heat the board until the asphalt melts to shiny black.
4.) Special offset printing press can print the board directly -- Coat it with asphalt, etc...
<nbucska@pcperipherals.com>
