How repeatedly make good PCB? Many hobbyists faces this issue every time they are prototyping their ideas. Designing the PCB layout (doesn’t matter is it a through hole or surface mount) may be tricky task especially when dealing with dimensions like 0.2mm tracks or 0.5mm surface mount pitches. Laser printer, plotting or other similar transfer technologies can’t deal with such dimensions.

After I have tried photographic method of PCB artwork transfer, I don’t even want to touch Iron and laser printer. Using photosensitive laminate and single transparent media I can repeatedly make any number of PCB’s. Benefits of using photographic methods are as follows:

• Transferred artwork is very clear, edges are smooth;
• Track thickness may be up to 0.2mm or even less with good mask quality, which can be made with good laser printer (usually new one). After printer cartridge refill – printing quality drops down;
• With one artwork mask I can clone many PCB’s;

Pay the biggest attention to artwork fabrication. Without good artwork you won’t be able to make good PCB. From My experience I can say, that I always do small mistakes with PCB artworks and I spot them usually after PCB is etched. Devote more time for PCB artwork tracing and you will save much more time while soldering.

The artwork should be:

• Clear;
• Sharp;
• Solid black when printed.
• Printed side should be in contact with PCB, so don’t put opposite as then you get blurred picture.

For Artwork transfer it is not necessary to use transparent media. Paper (UV translucent) can be good too. It may require longer exposure. Why I saying this? Because laser printers likes paper more than acetate film. The toner stays flatter on paper and black is smoother than on film. Especially using printers with refilled cartridges I would recommend use paper instead of film. I used to use film but results is rather disappointing than promising.

The printer itself should have following:

• Resolution at least 600 dpi;
• Should print good solid black with no toner holes;
• Pint accuracy should be good especially when printing double sided PCB artwork;

The next important thing in PCB development is Photoresist PCB laminate. It has to be good quality especially when dealing with small tracks. If you use pre-coated PCB, then inspect if there is no scratches in covering, check the PCB age. When handling just avoid direct sunlight and unnecessary light exposure. And develop just after exposure. If you decide to spray photoresist by yourself, remember that area should be clean from dust. It works for low resolution boards, but for higher resolution, I would recommend buying pre-coated boards.

Exposing of photoresistive boards are done under Ultraviolet lamps. This is not very critical issue, but still:

• Don’t use shortwave lamps;
• Use more tubes than one – this makes light more even;
• Use timer to make exact exposure timing.

For developing boards I don’t recommend to use sodium hydroxide. This is dreadful stuff. It is sensitive to temperature and concentration and it is aggressive chemical. It may easily strip all photoresist. Solution doesn’t last long. Better use silicate based products. This isn’t sensitive to temperature or concentration. It is hard to overdevelop. Solution lasts much longer and you can make stronger solution for faster developing. As this would be your PCB killing by using sodium hydroxide.

Fro etching I would not recommend to use ferric chloride. This is really messy stuff. But if so, then avoid any contact with metal as it attack almost any metal. Use plastic or glass tank. As better alternative use Ammonium persuphate. As this is transparent solution, doesn’t mess, it is not aggressive as ferric chloride. But it gives even better result in etching. It usually doesn’t etch under the track what is important when board is high resolution.

This is only generic guidelines of making PCB. Further I would recommend reading following sources:

AVR controlled signal generator-1 layer PCB prototype

Ultraviolet light source UV-80 for PCB exposure

PCB Etcher

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This entry was posted on Tuesday, June 13th, 2006 at 11:51 am and is filed under UV PCB Making. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.