There are several ways on how to build and develop an input-output isa card. This tutorial merely focus on the steps on how to develop an electronic circuit layout into the presensitized printed circuit board (a factory prepared PCB surface coated with a photo sensitive emulsion). Assuming that the circuit schematic and pcb layout is already available. If for instance you don’t have the knowledge and the basics of building a circuit, please take some time to know the steps on how to build a circuit for an input-output isa card.

top artwork transparency

bottom artwork transparency

Here are some steps for pcb development:

1. Make a good preparation for all materials needed. This step is the most important among all. Take some time to prepare all materials needed for the development. May it be for pcb developing, etching or drilling, it is better to have all that are needed which makes your work uninterruptedly, rather than working for a moment then spend more time looking for what’s missing and resume to work over time. Good thing for preparation is to have a check list. Here are some things that mostly needed fro circuit development.

For presensitized pcb development:

• Presensitized PCB (cut to size larger than the artwork)
• Circuit’s PCB Layout/Artwork (printed in transparencies/acetate)
• UV light (ultraviolet light) or Fluorescent light
• Coastic Soda (developing solution)
• Foam (cut to size smaller than the pcb)
• Plastic container (fit enough to contain pcb)
• Flat wooden support (old pcb)
• Soft drink cap (plastic)
• Rubber bands
• Paper tape

foam and support

developing powder

Important to note:

Examine the layout/artwork carefully. Check the lines for cracks and dark spots as it may result to open or short the circuit which may result to damage your project. It is advisable to use a laser printer to produce a crisp, solid, fine black prints on the artwork. Inkjets may produce crack, blurred lines which may result to open or short the circuit.

While in preparation, do not attempt to strip off the protective shield (gray film/sticker) of the presensitized pcb as it may unintentionally expose to sunlight.

2. Exposing the presensitize pcb. Slowly strip-off the protected film in a low light environment. Carefully place the artwork transparency above the pcb (make a good alignment by referencing to the straight edge of the pcb). Alignment is very important when developing a double sided pcb. Flatten the artwork with the use of thin clear glass.

stripping off pcb film

placement and distances

Using a rectangular shaped foam, supported with an old pcb or hard flex, compress the pcb and bind it with a rubber band (rubber band is good for holding and binding because of its elastic characteristic)

Let it be exposed in an ultraviolet light (uv light) for about 5 to 8 minutes depending on the type of light. If uv light is not available, you may use a clear 20 to 40 watts of fluorescent light in about 15 to 20 minutes of exposure.

If developing a double sided printed circuit board, repeat steps above. Always take a good look at the alignment of the artwork in all of the edges. Make the layout/artwork of the top aligned to the bottom artwork.

3. Developing the pcb using the developing solution. Prepare the developing solution by pouring 1 cap of developing powder and a 30 cap of water in a plastic container (do not use metal containers as it may produce a chemical reaction with your developing solution). Dissolve the powder by rocking the container. Carefully examine the solution, if white particles exist (there must be none), continue rocking.

Gently remove the rubber bands and the supporting thin glass. Avoid touching the surface of the pcb as it may scratch and ruin the layout on the pcb. If developing a double sided pcb, use a standoffs (can be made of a pvc folder clips) along the edges. This standoffs may be a good help to prevent scratches while developing is on progress.

materials placement and spacing

developing presensitized pcb

Submerged the pcb into the pcb developing solution. Make sure that the solution is enough to wash all uv exposed areas of the pcb. Carefully wash the pcb in the container by rocking it. The developing progresses as you may seen the green photo resist slowly washed away. Continue rocking until all unnecessary green photo resist disappears revealing the layout of the circuit. This may take 30 seconds to 15 mins depending on the amount of developing powder in the developing solution.

bottom pcb output developed

If still with no progress, carefully remove the pcb from the container, washed it with water and add a little more of developing powder in the developing solution. Dissolve the powder and again, soak the pcb into the container.

Rinse the pcb with running water to remove the developing solutions (this is very important as it will continue to remove the green photo resist and ruin the layout of the circuit). Continue washing for 30 to 60 seconds. Pcb is now ready for etching process.