Etching the board.

Now we have our board cleaned up and touched up if necessary it’s time to etch the thing.

It’s important to do some test boards with your chemicals to ensure that you get the mix right and also to get a rough idea of the timing you need to allow.

I’m using a mixture of Sodium Perborate and Hydrochloric acid. I’m not sure what the proper name or formula is for this mix. It’s the standard mix for sale here in Barcelona.
I make the mix up in a large ABS plastic container in a well ventilated space with plenty of water handy just in case. We’re talking about the kitchen here…

Hydrochoric Acid & Sodium Perborate
My chemicals

Place the board ready in the same container as before (emptied out and dried of course) and pour the etchant over the top of the board. Careful not to splash any.

Plastic tweazers are handy for handling the board. Note this
etchant is green as I have used it before, fresh mix is clear.
The etchant bubbles a little when you first put it in. I think it’s the
paper that causes this as later on the bubbles stop even though
the etching continues.
After a couple of minutes the etching is really starting to show.
All I’ve done is to give it a bit of a gentle agitation, no heating or
anything special.
A minute of two later we’re nearly there. The remaining copper is
very thin and won’t take long to disappear

After about 5 minutes we should be well on our way. There are bound to be lots of fine traces remaining which we need to keep an eye on to ensure that they are all etched away properly. I like to etch using a clear tub that I can shine a light through underneath. It makes watching the etch progress much easier. The exact timing probably depends on temperature, time of day, phase of the moon etc.

Just a little over 7 minutes and all that remains is a couple of thin patches.
Dunk it for a few more seconds and we’re done.

When you think you are done take your board out and rinse it under the tap. Hold it up to the light or against a window (in the daytime) to inspect it for copper bridges that may remain. You’ll need to use you judgment as to how you fix the any bridges. If they are quite extensive then you probably need to drop your board back in the etch bath for a few another minute. If however your board use lots of ultra fine traces and is pretty well etched on the whole then you don’t want to risk over etching. In this case you might be best off removing any bridges the manual way with a scalpel or similar.

Once your etch is complete pour the solution safely back into your storage container. (assuming that you’re not etching any more boards)

Ok, I know. I should have done this in the kitchen really.
The light was good in here for taking the photos.

Now you need to clean your board up to be ready to move on to the next phase. You can use just about any method you like short of sandpaper to remove the toner. Some people just use a scouring pad and some elbow grease, others, like me, go for the easy route and splash a bit of universal solvent into the deal. Either way, we just need to remove the toner so we can solder easily solder our components.

Golden Cat Universal solvent. I’m not certain what this is made from.
I think I’d rather not know.

This is the stuff I use. We’ve had it around the house for ages. It’s horrible stuff and melts just about everything, but it’s great for removing toner. It’s so old that the price is actually in Pesetas as well as Euro which puts it at circa 2002 I think.

A dab of solvent works its magic.
Best done in the kitchen
The board etched and cleaned up ready for soldering.
Here’s the board along side its sister board. The one on the right is for
the LED display, the one on the left is for the rest of the components.

Now we are finished. Your timings may differ, there are probably lots of influences such as ambient temperature, exact mixture etc. But for me it takes around 5 – 10 minutes to etch boards of this size and surface area.

Next step. Construction : But that’s for a later date as I have things to do.

I found an Epson Stylus Colour 1520 on the street that I’m going to cannibalize for all the goodies like stepper motors and switches.

6 thoughts on “Etching the board.

  1. Nice work, on both the board and the illustrated procedure.
    Regarding the areas of copper that etch slower than others, I’ve used a cheap paint brush to increase etchant flow over slow areas like that to speed them up.∂

  2. Hi Gary, That’s a good idea I’ll give that a try on my next go. I’ll have to find a brush that isn’t eaten by the chemicals.

  3. I’ve found out that cleaning of toner after etching will be easier if you soak piece of paper towel/fabric first then apply solvent to the board. You will not get any smudges like on your photo.

  4. Hi, I’m interested in your etching solution using Sodium Perborate and Hydrochloric acid. The reason is that I can obtain both at my supermarket, sold as muratic acid and laundry bleacher at very low cost. I would be curious to know what the correct mixture between the two would be. For instance, how many grams of SPB christals in one Litre of Acid?

    By the way I’ve got a tip for you as well: If you want to develop photosensitive PCB’s you can use NAOH crystals sold as plumbing tool in your super market to de-block up stuffed-up pipes. A mixture that works for me is 25gr/Ltr

    • Dear Jan

      I used hardware store “spirits of salt” (31% HCl) in about 3x its volume of water and added a little “Vanish Oxi action” bleaching washing powder (containing some % of sodium percarbonate). It foamed a lot to begin with (presumably CO2 evolution). I threw in some copper wire and left it overnight. This morning the wire is gone and I am left with a blue solution that looks a bit like CuSO4, perhaps a little more greenish but not as green as the pictures above. (Does CuCl2 solution become more green with increasing concentration or is there some other reason for the blue colour? I don’t know.) There solution is not clear as there are bits of white precipitate and some other crud floating about that I presume derive from other ingredients in the washing powder. But I think this could be a viable combination for etching Cu.

  5. You’ve written a very excellent article.
    If it’s ok with you, I would like to request permission to use your article as it relates to my problem. I will be glad to negotiate to pay you or hire you for this.

    With Regards from
    Republic Polytechnic

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s