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PCB's - Printed Circuit Boards
The NEHOC system can be used to make only small runs of PCB's, as this process involves harsh chemicals which are destructive to the RISO ScreenMaster screens. In most instances, the PCB is a one only production, making the NEHOC system perfect for the job.
A printed circuit board [PCB] is best made using the SP-275 ScreenFax and a ScreenMaster 135Mesh , however any RISO system using Print Lamps can also be used when B6 or B5 size Print Masters [i.e. NEHOC Screen Printing Kit]
Making your screen
Which ink to use
Talk to a screen printing ink manufacturer for advice about the correct ink to use. The ink must be able to resist the effects of the copper leaching chemical [Ferric Chloride, FeC13] for about half an hour.
In Australia, a suitable ink is Ultrasatin made by Colorpak Inks and Coatings (CIC) Pty Ltd.
Preparing & Printing the PCB
Before printing on the blank copper face of the PCB material, it must be washed thoroughly using methylated spirit. Be sure not to put your fingers on the copper area to be printed after washing.
Drying time will depend on the ink used and the weather, but inks are available which will be hard enough to resist the chemical after 15-30 minutes if the drying process is helped along briefly with a hairdryer.
Preparing the Ferric Chloride bath
Mix up a solution of Ferric Chloride with very hot water in the proportion 42% Ferric Chloride to 58% water. Ferric Chloride is available from chemical or pharmaceutical supply firms or [as a solution] from some electronic hobby shops.
Place the mixture in a suitable container, being aware that such a container should not be used again to contain food and that the solution is likely to stain the container.
If the weather is cold, put the container of hot Ferric Chloride into a larger container of plain hot water. This will help to speed up the process by keeping everything warm.
Carefully read and follow all warnings and safety instructions given by the packager of the chemical. Be sure that hot water will not melt or break the container and do not use a container made from copper or other metal.
It is a good idea to drill a small hole in the PCB material away from the design and attach a string so that the board can be pulled to the surface of the liquid and checked now and then.
With the printed design on the PCB material now dry, place it in the container of hot Ferric Chloride solution.
The container should be given a very slight movement ever few minutes to bring fresh solution into contact with the exposed copper surface of the PCB.
The whole process should take less than 30 minutes, but may take longer in cold weather or if a very large amount of copper needs to be leached away by the solution.
When you can see that all of the exposed copper surface has been removed from the backing board, take the board from the Ferric Chloride bath and rinse it well under a cold water tap.
Dry the board.
Removing the ink
With a cloth dipped in a suitable solvent [usually either turps or methylated spirit], remove the printed ink design from the board. The copper on which the ink was printed, having been protected from the leaching action of the chemical by the ink, will then be exposed and the printed circuit board is ready for use.
If the PCB item you have made is not to be used with electrical connections, it should be sprayed or painted with an art varnish or a clear lacquer to prevent the copper from tarnishing. Printed circuit boards for use as electronic components should be tinned with solder.
comments by Sebastian Hegarty - ZDL Computing
In addition on more complex circuit boards its impractical to 'tin' the whole board although not impossible [especially in RF circuits], you should either use a Circuit Board Lacquer which can be soldered through and still protect other areas or use a reversed filled layer 'mask' which will only expose the contacts, this is how and why circuit boards appear green, red or whatever colour, after this you can tin the contacts.
This process can also be used to produce the "silk screen" layer; this is the component layout map on top of the coloured mask.
Printing pictures onto PCB's
You can use this method to make logos, coats of arms, shields etc: from PCB blank material. Several colours are available in the PCB backing sheet to which the copper sheet is bonded, so that the copper design can be put onto material with a black or other coloured background.
If the PCB item you have made is not to be used with electrical connections, it should be sprayed or painted with an art varnish or a clear
lacquer to prevent the copper from tarnishing. Printed circuit boards for use as electronic components should be tinned with solder.