I finally made the PCB for the QuadroCopter drone me and my friend are making. Today I produced about 5 PCBs, 3 of which didn’t turn out. So in this tutorial I’ll go through what I did so if you’re Googling around and come here for tips, you’ll get to know what works and what doesn’t. One out of the 5 PCBs came out right the first time, this was for another project however. For the Quadrocopter mainboard, the pcb needed to be smaller. The UV method vs iron on transfer method needs presensitized copper clad boards vs standard copper clad boards.
Giving the PCB a Developer Bath
The basic process goes like this. UV light is exposed to the presensitized copper clad boards. The transparency blocks traces that you want to leave on the board. When the board is immersed in the developer solution, the green enamel is dissolved away wherever light was exposed. Then, wherever there is no enamel and just copper, the copper can then be eaten away with the etchant solution (usually Ferric Chloride) leaving only the green traces left. The pads and vias can then get their green enamel removed manually using acetone.
Work area, plexiglass on top of the UV light which is turned off. Red LED for visibility without exposing the PCB to UV light. And PCB shown under the light sandwitched in the transparencies. Power supply on the left powers the LED.
When you buy presensitized boards, they come in a black plastic sleeve and have stickers on both sides to protect from UV light. The board can be taken out of the black sleeve and cut using a Dremel or Exacto knive. Next in a dark room you can pull the sticker off. However do this without exposing UV light yet. A red LED is perfect for lighting up the area you want to see similar to producing film photography. Your Eagle CAD drawing should be printed on transparency paper. The side with the toner should be facing the PCB. So make sure its printed correctly. If its a double sided PCB the transparencies should be taped together and the PCB sandwiched in the middle and the board should not be allowed to move around. Place a piece of plexiglass on top of the transparency so that the transparency is nice and evenly flat against the PCB. Then turn on the UV light. I set a timer for 8 minutes on my blackberry. When thats done, flip it over without the PCB moving around inside the transparency sleeve and let it sit for another 8 minutes.
Aligning the PCB within the transparency sandwich.
Things can go wrong. If you make your cuts on the PCB using the Dremel, the edges may be jagged giving the board some extra height on one end making the transparency not so flat. This blurs the exposure of the UV light rendering many PCB traces unusable. This happened twice. The first time I thought it was because I left it in the developer solution for too long, so I did it again to find out that the edges were jagged. PCB may show defects. Make sure the transparency, board and everything is entirely clean. Dust and particles can block exposure to the UV light. Scratches in the transparency where the print is may over expose some areas and make traces broken. The PCB can still be used if this happens, except you have to make repairs to the traces. Make sure the plexiglass rests flat on the PCB!
This board didn't turn out well. The bottom and right edges were cut and left jagged instead of grinded smooth. This caused the plexiglass to not have a flat surface across the transparency. Notice towards the bottom right corner of this pcb their is a shadow. This is wrong.
After the exposure is done, dip it in the developer solution. Agitate the liquid a bit, and use a foam brush to go along it. Flip the board frequently if it is a double sided board. Once it comes out clean, rinse it and dip it in the etchant solution. Vibration/Agitation, air bubbles and heat speeds up the etchant process. Do not heat Ferric Chloride any more than 55 degrees Celsius. I heated my ferric chloride in a plastic bottle for 30 seconds. Wear all safety things, gloves, mask, protective glasses. I used nitrite gloves as they are better at handling chemicals then regular latex gloves. Plus the nitrite gloves were cheap. Be very patient with the etchant process. Its not going to be done instantly or as fast as the developer process.
PCB in developer solution.
PCB after developer bath, before etchant bath.
Finally use acetone to wipe away the green enamel around the vias and pads or everything if you wanted. Drill the holes and mount the comments. I would do the SMD stuff first, especially the ones that need the reflow process done to get them soldered.
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Good article, however you didn’t list the chemical(s) you used to develop the board after the UV exposure. This is the piece of critical information i am searching for.
So far I’ve read one article which said NaOH works good but another that said its too error prone, so im still searching for a consensus.
I used a PCB “Developer” solution. I was also wondering what the proper name for the chemical was, but it was just labeled Developer. You’ll find it wherever presensitized boards are sold.