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[Tutorial] UV PCB Transfer & Chemical Etching

PostPosted: 12 Apr 2010, 15:35
by lolbou
Hi ya all. Here's a detailed method of etching that I use. In this How To, I'll explain what's going on from a chemistry point of view, and what are the dangers that you might need to protect from. There are many different ones already all over the internet, but I hope this one would be clear and helpful to many of us... (edit: you can find some similarities with bajaman's thread here, though the etchant is not the same... :wink: )

So here we go.

You need:
- Your circuit laser-printed on a transparency (reversed so that the printed side is in contact with the copper).
- UV light (I use an adapted facial sun lamp mounted as an UV box).
- Presensitized copper clad.
- A 7g/L sodium hydroxide solution (made from a more concentrated solution that's quickly available in DIY stores).
- Hydrogen peroxide (I use a 110vol (=33%) solution) (10€/L)
- Chlorhydric acid (23%) from the DIY store (1€/L)
- A bucket of water (you never know).
- Some acetone and cold tinning solution if you want your PCB to be cold tinned.
- Gloves and glasses in a open area...

Nota bene: you may use a less concentrated peroxide solution (like in the video above). I have to try it myself to tell, but it may be less harmful and provide a more gentle etching...

1) Preparing the PCB:

Cut the PCB to size, and file the edges with sandpaper or a file...
img_2828.jpg


Then peel off the protective film.
img_2829.jpg


Place the resin-side onto the transparency.
img_2831.jpg


Close the box an turn the UV light on for the appropriate time (For me it's 1'45", but it depends on your equipement).

What's happening: well, the UV light will degrade the exposed resin. Since your printed image blocks the UV light, then it will remain intact, which will be useful afterwards.

You can now put your gloves and glasses.


2) Removing the exposed resin:

When the exposure is done, you have to dip your PCB into the sodium hydroxide solution to get rid of the degraded resin. This step takes up to 30 seconds.

From the start:
img_2836.jpg


And then the circuit lightly appears:
img_2837.jpg


And it's over now:
img_2838.jpg


You rinse it nicely, and you can see now the copper sheet with your circuit in resin up above. This resin will protect the future tracks from being etched...
img_2841.jpg


3) Etching the copper:

I use a 50/50 of acid and peroxyde mix. Recipes may change, affecting mostly the speed of the etching, but the chemistry is the same.

For this How To, I used 25mL of each reactant. No more is needed. You can even lower the quantities provided your etching tank is deep enough...

Open the window or go outside. Dip your PCB in the mix. It bubbles instantly and the solution turns green-blue.
img_2842.jpg


Very soon (10" in my case) it's all done. I did it at 15°C/60°F, but it was slower this winter...
img_2844.jpg


Dispose of your etchant by pouring it in the bucket of water. This turns your etchant in a harmless solution.

You have it now. You can solder on the resin if you like. I'd rather tin the PCB, but I'll detail it after the chemistry part...

Re: How to etch a board with peroxide (UV method).

PostPosted: 12 Apr 2010, 15:49
by lolbou
Now the etching chemistry...

When you mix your peroxide and acid, a reaction takes place instantly. Even if there's no copper. When you will put your copper PCB in this mix, two reactions will compete.

Here are the semi-équations for each element:

H2O2 + 2H+ + 2e- => 2H2O (E1=1.77V)

Cl2 + 2e- => 2Cl- (E2 = 1.396V)

Cu2+ + 2e- => Cu (E3 = 0.340V)

The bold elements are those present in the mix. From these equations, we can say two things:

- peroxide will react with chloride ions to give chlorine and water. Considering the low difference between their potentials E1-E2 = 0.374V, this reactions is not very efficient, though it is happening.

- peroxide reacts with copper to give copper(II) ions and water. Since the potential difference is way bigger here (E1-E3=1.43V), this reaction will be way more efficient.

Chlorine is a green and very toxic gas. Breathing large quantities can really be harmful. But with this low volumes and short time of reaction, you can safely etch, provided you open the window or work outside. And if you use less concentrated peroxide solutions, then the gas production is spread over a longer time, making it even more safe.

Re: How to etch a board with peroxide (UV method).

PostPosted: 12 Apr 2010, 15:57
by lolbou
Now back to the cold tinning. I use a readily available cold-tinning solution. A bottle lasts quite long since you put the liquid back in the bottle after tinning.

Here's the method I use (still with gloves and glasses)

- Remove the resin with acetone. I dip it entirely so that no traces are left on the copper. If you remove the resin by spreading it with a cloth, you get bad results afterwards.
img_2845.jpg


The resin dissolves instantly.
img_2846.jpg


And you get the naked copper...
img_2847.jpg


Rinse nicely. And then dip your PCB in the solution for 1 minute.
img_2848.jpg


Rinse again and put the solution back in the bottle. It is tinned!
img_2849.jpg


Now, look at that happy DIYer...
img_2851.jpg


ps: ensure some clear space and work quietly, especially if you're not confident about the harmful stuff. The clearer the space, the safer the experiment. My garage is a mess at the moment, my bad. But do yourself a favor and be safe!

Re: How to etch a board with peroxide (UV method).

PostPosted: 14 Apr 2010, 04:42
by ramaneek.gill
All i have to say is...
WOW!!

An amazing tutorial, I've never tried that method before, this pic by pic tutorial really helps us n00bz out there
thanks :)

Re: How to etch a board with peroxide (UV method).

PostPosted: 14 Apr 2010, 14:42
by lolbou
ramaneek.gill wrote:All i have to say is...
WOW!!


Thanks!! :D

ramaneek.gill wrote:An amazing tutorial, I've never tried that method before, this pic by pic tutorial really helps us n00bz out there


Yeah, you don't have to be fearful about the chemicals and stuff, as long as you use the adapted protection. By the way, a box of 100 gloves costs 10€ euros at the chemist's here in France... This method can be less strong if you use low concentrated peroxide, but still with good results, and no bad stains or disposal problems as for the iron perchloride...

Maybe I should post about the making of the UV-light box... :scratch:

Re: How to etch a board with peroxide (UV method).

PostPosted: 14 Apr 2010, 23:15
by ramaneek.gill
lolbou wrote:
ramaneek.gill wrote:All i have to say is...
WOW!!


Thanks!! :D

ramaneek.gill wrote:An amazing tutorial, I've never tried that method before, this pic by pic tutorial really helps us n00bz out there


Yeah, you don't have to be fearful about the chemicals and stuff, as long as you use the adapted protection. By the way, a box of 100 gloves costs 10€ euros at the chemist's here in France... This method can be less strong if you use low concentrated peroxide, but still with good results, and no bad stains or disposal problems as for the iron perchloride...

Maybe I should post about the making of the UV-light box... :scratch:


You definitely should! :wink:

Re: How to etch a board with peroxide (UV method).

PostPosted: 16 Apr 2010, 05:08
by Grendahl
I agree, I'd definitely love to see the how-to on the lightbox as well.
:secret:

Re: How to etch a board with peroxide (UV method).

PostPosted: 16 Apr 2010, 22:36
by lolbou
Grendahl wrote:I agree, I'd definitely love to see the how-to on the lightbox as well.


Done! :wink:

Re: How to: etch a board with peroxide (UV method).

PostPosted: 17 Apr 2010, 07:17
by RnFR
i've got to get me one of those jackets!

Re: How to: etch a board with peroxide (UV method).

PostPosted: 17 Apr 2010, 07:32
by lolbou
RnFR wrote:i've got to get me one of those jackets!


You won't be able to live without it... :mrgreen:

Re: How to: etch a board with peroxide (UV method).

PostPosted: 21 Apr 2010, 19:36
by chicago_mike
I think I can.. :P

Re: How to: etch a board with peroxide (UV method).

PostPosted: 21 Apr 2010, 22:08
by lolbou
chicago_mike wrote:I think I can.. :P


You BELIEVE you can... :secret:

Did you find the info useful here Mike? I remember you've been wondering a lot about PCB making in past...

Re: How to: etch a board with peroxide (UV method).

PostPosted: 21 Apr 2010, 22:16
by Duckman
lolbou wrote:I use a readily available cold-tinning solution.


What do you use? (If it's not a secret! :D ) I can't found Tinnit any more! :cry:

Re: How to: etch a board with peroxide (UV method).

PostPosted: 21 Apr 2010, 22:23
by lolbou
This from www.cif.fr . I found these at any local electronic shop.