PCB Manufacture
A major stumbling block for me was PCBs. I did a little hunting on the WWW and decided to make my own using positive resist board and PC artwork. Main points:
- Use a bubble-jet or ink printer, not a laser. Lasers will leave gaps in the solid track lines when printing onto overhead transparency material.
- Buy purpose bubble-jet overhead film. It is quite expensive relative to standard OHT film, but the results are miles superior. Given the effort involved, $1 for a sheet of film is nothing.
- Check the printed PCB positive against a strong light before using it for exposure, in case there has been a line missed by a blocked jet. Use a permanent OHT pen if required.
- For my Aleph4 I used commercial positive resist board from Farnell, along with their developer and etching solution (granules). This comes with a black plastic peel-away covering on the treated side. For the Aleph5 I found a much cheaper source of good quality PCB manufacture materials.
- Buy a couple of cheap plastic "lunch boxes" for the solutions.
- Get some thin (1-2mm) plastic sheet (not glass) to place over the film on the board so it lies flat and does not move. Obviously you don't want refraction around the edges and a fuzzy result.
- For exposure I used midday sunlight. Now, living in Australia this is easy. Make a small test film. I used a simple text message "Testing" at 12 point and trial exposed at various times on small pieces of PCB prior to doing the main boards.
- For the Farnell PCBs it turned-out 5 minutes in the sun was perfect, but then it was a 38°C day (around 100°F!). On another day for the FET boards it took 8 mins.
- For the Kinsten product exposure requirements were much less and 2 mins in mild winter sun was sufficient. I would recommend using this product if you are in Oz.
- NB: Do not mix systems - I tried to use the developer from Farnell with the Kinsten PCB and this didn't work so well :-(
- Place in the developer solution for as long as it takes to clear the unwanted protective film. This is quite quick and is aided by rocking the solution slowly.
- Make your etching solution as per the pack instructions. Please don't ignore the safety instructions re eyes etc !!!!! Place the boards in and rock the solution gently. I found using a cheap plastic disposable paintbrush helpful.
- If you use FR4 based board, standard drills will blunt quickly. I bought a cheap set of tungsten tipped drills for the purpose.
- Try to find a drill press, it makes the task a lot neater and easier.
Having never done this before I was very pleased with the end quality of the boards and I would encourage any would-be-builder to try this if they don't have access to proper facilities. In fact, it was the success with the main boards which prompted me to make the custom mounting PCBs for the FET sets.
|
