Friday, December 17, 2010

Making PCBs: Ideas for improvement

As you might have seen in my videos about the Pill Reminder Project, my self-made PCBs look rather unprofessional and soldering is a mess. This is due to the method I currently use. It's cheap, fast and easy, but also limited:
  1. Print the layout on glossy paper using a laser printer.
  2. Place the printed side on the copper surface of the board, fix with (non-plastic) tape.
  3. Use a regular iron on maximum heat to transfer the toner to the copper surface. (Don't remove the paper yet!)
  4. Place the whole thing into warm water, add some soap. Wait.
  5. Carefully(!) remove the paper using your fingers, without damaging the toner layer. If the toner comes off, you didn't press hard enough when ironing.
  6. Etch using your favorite etchant. I use sodium persulfate.
  7. Remove the toner with a circular brush tool.
The main problems are:
  • High clearance needed because tracks increase in witdh due to squeezing.
  • Lots of corrections needed because toner tends to flake off during etching.
  • Due to the high number of repairs that need to be done manually, a solder resist mask cannot be used.
I used this method because it could be done without buying extra equipment. I will continue using it for prototypes because it is fast. Also it allows for corrections everywhere, such as adding parts, because there is no solder resist mask. However, I plan to make a second version of the pill reminder where the PCB, due to the use of SMD parts, fits entirely under the pill box. Squeezing and lack of solder resist are inaccaptable for SMDs, though.

That's why I am going to implement the standard photoresist process plus cemical tin coating and solder resist through laminating. However, I need to buy or make some equipment to do so:
  • UV Lamp
  • Laminating machine
  • Inkjet transparencies
  • Solder resist lamination stuff (e.g. Dynamask)
  • Various chemicals (for developing, etching and tin-coating)
So stay tuned for some videos and posts about how I make all the stuff I need. (The laminating machine probably needs to be modiefied to eat PCBs). When I got everything in place I will make a tutorial on how to make PCBs using my new process. (Note that most of my viedeos aren't meant to be instructional videos. They just show how I solved the problems that I had. However I may make real instructional videos from time to time)

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