There are various methods to create PCBs, and using dry photoresist film offers a convenient and cost-effective solution.
The step-by-step process of making a PCB using dry photoresist film.
Materials Needed:
- Copper-clad PCB board
- Dry photoresist film
- UV exposure unit
- PCB layout design (printed or digital)
- Chemical etchant (e.g., ferric chloride)
- Developer solution (Sodium carbonate, sodium hydroxide etc)
- Etching tank or tray
- Protective gloves and eyewear
- Fine-grit sandpaper
Step 1: Design and Print the PCB Layout
In the image below you can see the PCB. I first designed the layout and then i printed the layout on a transparent OHP sheet using a black laser printer.
Step 2: Prepare the Copper-Clad PCB Board
Then I cut a piece of Copper Clad board.
Then I cleaned the Copper Clad board first by scrubbing using a kitchen utensil scrubber which has a small grit size. I also applied utensil cleaning powder as a compound. Which is basically calcium carbonate(CaCO3).
Clean the copper-clad board with fine-grit sandpaper to remove any dirt or oxidation. Ensure a smooth and clean surface for optimal adhesion of the dry photoresist film.
Step 3: Apply the Dry Photoresist Film
After that, I cut the photoresist film. Then I peeled the protective plastic from it. And placed it on the PCB. I then used a visiting card to squeeze out any air. I ensured it is as smooth as possible.
Then I place it on a wooden plank and covered it with a piece of cotton cloth. And I applied Hot cloth iron (Set the temperature setting for Cotton). While I applied it I also put some pressure so that it get stuck to the PCB.
NOTE: it is a very delicate process. Only by trial and error, you will find the right temperature setting and duration of heat application.
Step 4: Expose the PCB to UV Light
After that, I placed the OHP sheet cutout which has the layout printed on it. Then I put this sandwich of PCB and OHP under a homemade UV box.
The UV box is made from a shoebox that has a Phillips UV tube light strapped on the side using two zip ties. I do not remember the exact timings now, but it is somewhere between 1 minute to 2 minutes.
Step 5: Developing Photoresist Film
After that, the Copper clad board with photoresist is put into a solution made of water and sodium carbonate.
Why sodium carbonate?
Because at that time there was a lockdown so that’s why.
Sodium carbonate was the only chemical available at that time for the development of the photoresist.
NOTE: You need to develop the photoresist in a completely dark room or under red light(zero-watt bulb).
Step 6: Etching the PCB
After the developing process, you can put it into the etching solution made of water and ferric chloride. Make sure to vibrate the solution. As it will fasten the etching process.
Note: you can set up a double boiler for faster results.
I place a stainless steel vessel filled with water on an induction stove. and placed another plastic bowl filled with the etching solution and the PCB, inside the stainless steel vessel. Remember to heat it slowly as you want the etching solution to heat up every so slightly and not vapourize.
Step 7: Removing Photoresist
After the etching process is complete. You need to remove the photoresist film.
You can remove the photoresist by various methods :
- Sanding the photoresist using sandpaper (abrasive paper).
you use a high grit for better results. - Use Lye or sodium hydroxide solution
Make a solution of sodium hydroxide and water in a container and dip the PCB in it. The solution will dissolve the photoresist. And then you can wash it in running water under a ceramic wash basin.
I did not have sodium hydroxide as Lye available. So I improvised and used the “HARPIC bathroom cleaner” which has a small percentage of sodium hydroxide in it.
Step 8: Drill Holes and Solder Components
Using a drill with PCB drill bits, create holes at the designated locations on the PCB for component mounting. Ensure the hole sizes match the component leads or pads. Once drilled, solder the components onto the PCB following standard soldering techniques.
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