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Etching your own copper panels #6: Etch and Finish

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Blog entry by splintergroup posted 11-02-2016 06:57 PM 773 reads 0 times favorited 7 comments Add to Favorites Watch
« Part 5: Exposing and Developing Part 6 of Etching your own copper panels series no next part

Here we are with a etching acid resist applied to the PCB:

Next step…..

Etching
Simply stated, the etching process needs to remove any copper that is not protected by the resist applied during the previous steps. Copper is very reactive to acids. Traditionally the primary chemical used for PCB manufacturing was Ferric Chloride (FeCl3). I have a “stash” of this stuff from the 1980’s. It works well, but I’ve noticed that it is fairly expensive now ($8/pint, powder or liquid). A pint will etch about 200 square inches of standard (1 ounce) copper. I Have it so that is what I’ll use.

The down side to Ferric Chloride is that in reacting with copper, it turns into Cupric Chloride which is somewhat nasty (i.e. don’t dump out down the drain!)

I take my leftovers to a place that deals with them. I strongly suggest that you look into using muriatic acid as a cleaner alternative (see “Alternatives” at the bottom). I plan to do this when my stash runs out. It should actually be cheaper as well.

To neutralize the FeCl3 (from a manufacturers website)

The solution must not be put down the drain because of residual copper ions left in it. To make it safe for disposal, you can add sodium carbonate (washing soda) or sodium hydroxide to it to neutralize it, until the pH value goes up to between 7.0 and 8.0, testing it with indicator paper. Copper will be deposited as a sludge. Allow the sludge to settle, pour off the liquid, further dilute it with water and then it can be poured down the drain. Collect the sludge in plastic bags and dispose of it as required by your local waste authority.

Any etchant will work faster when warm versus cold. You don’t need boiling hot, but room temperature should be a lower limit. Manufactures suggest 135 F degrees as a good upper temp limit.
Use all precautions when etching (eye protection and gloves are the biggies). Ferric Chloride stains everything.
I keep a 5 gallon bucket of water handy for rinsing.

I pour about an inch of etchant into a plastic/glass pan and carefully (no splashing) slide my panel into the mix:

It is very opaque, so you need a way to retrieve the panel periodically to check progress. A pointy wood stick works well. I have two panels in this pan and for some reason the panels like to drift around and settle on top of one another. This keeps the panel on the bottom from being exposed to the etchant and delaying the process.
It is best to either do one panel at a time or be vigilant about keeping them apart. Be careful when you manipulate the panes to check or move them, you do not want to scratch the resist!

My etchant solution is almost worn out so it took about 5 hours to complete. Fresh, warm solution can work in a little as 20-30 minutes. Note that 2 ounce copper will take about double the time of 1 ounce.

I carefully lifted the panel with a stick to check on the progress. Here it is as it approached completion:

Notice the black fiberglass beginning to show through. At this point I’ll check every few minutes until it looks complete.

At that point, i’ll remove the panel and rinse it off in the water bucket. I’ll then inspect the edges and check fine details. Often after the large areas are stripped of copper, the small areas will still need further time. This was the case with my panels, the “A”s were a bit stubborn.
If you leave a board in the etchant for too long, the acid will begin to eat under the resist from the sides. You can lose fine/narrow details if this happens.

Finally Done!

At last the board is fully etched. A cleanup with water and….

Viola!

Remove the Resist

Now to remove that acid impermeable paint. Lacquer thinner will not touch this stuff once it is exposed to UV. The “remover” for this is a strong alkaline, household Lye (drain cleaner) works very well.

I buy the 100% stuff since I don’t want any foaming or other unexpected reactions (from the hardware or big box stores).

I shouldn’t need to tell you that Lye is nasty stuff. Eye protection, gloves, and please, do this outside!

The mix is 1 quart water to several TBSPs of Lye (basically the same mix as the washing soda developer).
Room temperature water is fine (and safer than heated water).

Slide the board into the solution. A fresh solution will look like this:

After a few minutes, the resist will rather suddenly start to peel away from the copper

Give it a minute or two from this point and then transfer the panel to your bucket of water for rinsing.

I had four panels and stripped each one individually. The first panel took only 3 minutes, the last panel took closer to 10 due to the weakening of the solution.

Here are the panels, completely free of resist:

The copper will begin to slightly oxidize from all the chemicals. I give the finished panel a scrubbing with #0000 steel wool to brighten things up and give an even matte finish to the now exposed fiberglass.

The panel will need protection if I intend to keep the copper bright. A spray of polyurethane or lacquer does the trick.

That’s All Folks!
I haven’t decided if I’ll create a patina, if so I’ll detail it in the project writeup for these panels.

Alternatives

As stated, the Ferric Chloride I use is rather expensive (still easy to find however). An alternative is pool cleaner (muriatic acid) and hydrogen peroxide. Way cheaper, but you still need good skin/eye protection. I’ve never tried this so no opinion, but when I run out of FeCl3, I’ll give it a go!

Thanks for following along!

A quick note on patinas

CaptainSkully was interested in the color shifting that appears on some copper pieces. I have seen this on copper plumbing when soldering (i.e. applying heat). I have also used heat as part of the patina process while experimenting.

The copper panels used in this project have a thin layer of copper bonded to a fiberglass core. They are designed for limited heat application during their use in electronics, but I’ve never tested those limits.

So, what to do?

I took a previously etched spare panel and applied some indirect heat with a propane torch:

(Taken with a handheld macro lens so a bit blurry, sorry!)

You can indeed see bands of color. This was done by very carefully waving the flame across the copper. It is very thin and will heat up very quickly. You may get a cool color on one swipe, then it will disappear on the next pass, very fickle!

Anyway, do this too much and the copper to fiberglass bond fails and basically the panel is destroyed, but when successful, I like the look!



7 comments so far

View AandCstyle's profile

AandCstyle

2885 posts in 2072 days


#1 posted 11-02-2016 10:24 PM

Splint, thanks for the very educational blog. I will watch for your patina lessons. :)

I hope that you aren’t intending to gamble with Fertility. :D

-- Art

View Redoak49's profile

Redoak49

2853 posts in 1803 days


#2 posted 11-02-2016 10:24 PM

Very well done blog series…...Thanks

View Mean_Dean's profile

Mean_Dean

5624 posts in 2962 days


#3 posted 11-03-2016 01:25 AM

Thank you very much—this is a great blog series!

The clock faces I’m considering etching would be the reverse of your results here. I’d want to keep the copper on the face, and etch the numerals and A&C details, similar to this clock face (by fellow LJ, pashley):

Thanks again for posting this—I’ve favorited it, and will refer back to it, when I try a copper clock face!

-- Dean -- "Don't give up the ship -- fight her 'till she sinks!" Capt James Lawrence USN

View splintergroup's profile

splintergroup

1638 posts in 1037 days


#4 posted 11-03-2016 02:39 PM

Dean, that clock sure is purdy!

Yep, that is how I would do it, the numbers and artwork are etched out.
The numbers and ‘tick’ marks would be easy enough, I’d use a drafting program like I mentioned previously. Heck, I’d bet that Sketch-up would do fine if the font could be installed (and I could get over that initial learning hump)

The circle shape would be done on my router table. I’ve done this before by bandsawing the circle shape close to the final diameter, drilling the hole for the clock motor shaft (typically 5/16” or 3/8”), then using this hole and the pin on my circle cutting jig. I’d double-sided tap on some grab blocks to keep the disk under control while routing, that PCB material is slippery stuff!

View CaptainSkully's profile

CaptainSkully

1517 posts in 3373 days


#5 posted 11-03-2016 03:23 PM

Awesome! Thanks for doing this. This is one of the best tutorials ever!

Bleach (from grocery store), muriatic (from Home Depot), oxalic (from marine store) are all different strengths of hydrochloric acid (HCl). I used muriatic to artistically etch some galvanized corrugated roofing for an outdoor piece, which worked well.

I’ll be doing a square face with one of the several free Arts & Crafts fonts I have (e.g. Glasgow, etc.). At some point, when I’m actually a homeowner instead of a renter, I’ll be tackling a tall case clock like they did on New Yankee Workshop years ago and The Wood Whisperer did more recently. This option really adds that custom touch.

One thing I’d like to know in addition to the material covered here is how to do that really pretty, multi-colored patina I’ve seen at craft fairs. Copper can go from green to blue to red given the right treatment. I’ve also seen copper treated with open flame to bring out colors. Any advice on these?

-- You can't control the wind, but you can trim your sails

View splintergroup's profile

splintergroup

1638 posts in 1037 days


#6 posted 11-03-2016 04:29 PM

Thanks Cap’n!

One thing I d like to know in addition to the material covered here is how to do that really pretty, multi-colored patina I ve seen at craft fairs. Copper can go from green to blue to red given the right treatment. I ve also seen copper treated with open flame to bring out colors. Any advice on these?

- CaptainSkully

This site has a good mix of patinas and is well organized. Plenty of other sites with more specific and home-brewed techniques.

My mission floor lamp used a mix of ammonia/heat/vinegar/heat to get a fairly robust patina. (difficult to see)


Mainly I just played around with heat and stuff I had handy. The ammonia did a fantastic deep blue with the heat.

Heat seems to be the key to getting the color shifts without any ‘chemicals’. The copper plating in PBC material is tough and can withstand a fair amount of heat. I’ll try some scraps and see what can be done (heat source is a propane torch).

The downside to chemical patinas with PCB material is the patina tends to propagate off of the copper and onto the exposed fiberglass. I’d love to get a nice verde, rough texture that is easy to do with vinegar, salt, and sawdust, but the crusties tend to stick well to the fiberglass making it impossible to clean up the background.

View splintergroup's profile

splintergroup

1638 posts in 1037 days


#7 posted 11-03-2016 09:15 PM



Splint, thanks for the very educational blog. I will watch for your patina lessons. :)

simple enough, just let it sit in some dank shop corner until it looks absolutely funky 8^)


I hope that you aren t intending to gamble with Fertility. :D

- AandCstyle

The message is purely subliminal, based on my email spam bucket, the technique is obviously very popular!

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