Sponge method for etching PCBs?

Thread Starter

spinnaker

Joined Oct 29, 2009
7,830
When I make PCBs I place the PCB in an etchant bath and agitate the bath.

I saw a video on line for making PCBs and in the video they poured just a small amount of etchant over the PCB and rubbed the board with a sponge.

Has anyone used this method? Does it work?

Seems there would be a lot less waste using this method.
 

thatoneguy

Joined Feb 19, 2009
6,359
If you don't mind a rather large mess form the spray when sponge 'flicks' the edge of the board, it's not bad. Don't use in a sink, etc. Basically do outside.

The Friction + Agitation does go a bit faster, at the same time, when working on larger projects, areas/shorts can be overlooked easily. The latter is why I still soak mine with Ferric Chloride. The Peroxide based etchants just aren't as good, or when they are, it is only for a small time window before it needs diluting again.

Fastest: Friction + Agitation in a spray etchant tank, the professional level stuff costs quite a bit though, but it works very fast by heating up the etchant, then sprays it against the board at a high pressure in a fan shape (like a car wash).
 

nerdegutta

Joined Dec 15, 2009
2,684
I'm using Natriumpersufalt. I have it in a plastic container, and the container in a pot/souce pan on the stove, under the ventilation fan, in the kitchen. So I heat it up to around 40-50 degrees Celsius. The time it takes to etch, is depending on how many times I've used the etchant, and the heat.

(BTW: My girlfriend is very patient with me, when I turn the kitchen into a etching laboratory.)
 

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jpanhalt

Joined Jan 18, 2008
11,087
I use mainly full immersion too. A sponge is helpful if you have a stubborn spot that is etching more slowly than the rest of the board, and you don't want to risk over etching the whole board. Remember, the etching process actually involves oxidation of the copper. Thus, agitation and rubbing a thin layer in air increases the speed.

Some people swear by the sponge method. You can get fine detail, and it is used by artists doing copper etching for that reason.

John
 

Wendy

Joined Mar 24, 2008
23,415
Never done it, might try it sometime. The problem I perceive is most of my etch resist is fairly fragile, it isn't meant to stay after all.
 

jpanhalt

Joined Jan 18, 2008
11,087
I use the photoresist method. It is quite tough. John

Edit: There is also what is called the Edinburgh etching recipe. It contains citric acid, which apparently complexes with the metal oxides, reduces sludge formation, and speeds up the process. See: http://www.nontoxicprint.com/etchcopperandbrass.htm

I tried it for a few boards, but switched to cupric chloride before I had formed any strong opinions about it. If you are into experimentation, though, it is worth a try.
 
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shortbus

Joined Sep 30, 2009
10,045
I've only etched one board but I used ferric chloride and while board was in the bath I slowly wiped it with a disposable foam paint brush. It worked great!
 

bertus

Joined Apr 5, 2008
22,270
Hello,

A soft brush or a soft sponge can be used for speeding up the etching.
I have used some tissue paper instread of the sponge.
It is cheap and disposable.
Always use protective gloves when using the sponge.
Also take good care of the correct disposal of the used etchant and the used sponge or brush.

Bertus
 

MrChips

Joined Oct 2, 2009
30,720
I'm using Natriumpersufalt. I have it in a plastic container, and the container in a pot/souce pan on the stove, under the ventilation fan, in the kitchen. So I heat it up to around 40-50 degrees Celsius. The time it takes to etch, is depending on how many times I've used the etchant, and the heat.

(BTW: My girlfriend is very patient with me, when I turn the kitchen into a etching laboratory.)
In english, that would be sodium persulphate (or persulfate). Do you add sulfuric or sulphuric acid (H2SO4) or hydrochloric acid (HCl) ? What do you do with the used solution? Have you tried rejuvenating it with more acid and hydrogen peroxide (H2O2)?
 

nerdegutta

Joined Dec 15, 2009
2,684
In english, that would be sodium persulphate (or persulfate). Do you add sulfuric or sulphuric acid (H2SO4) or hydrochloric acid (HCl) ? What do you do with the used solution? Have you tried rejuvenating it with more acid and hydrogen peroxide (H2O2)?
I'm only dissolving it in water. When it's used a few times, I store it in plastic bottles. After awhile it crystallize on the bottom. When I have a few bottles, I deliver them to a disposal center, and say what it is. The guys working there don't have a clue of what I'm talking about, so they tell me to put it near the lead acid car batteries.

I have occasionally mixed in more, but most often I make a new solution.
 

MrChips

Joined Oct 2, 2009
30,720
I use ammonium persulfate with hydrochloric acid added, heated to about 80C. When the solution starts to slow down, I add more HCL and H2O2. I just keep on getting more and more etchant.

 
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nerdegutta

Joined Dec 15, 2009
2,684
I'm expanding my horizon, and have started to use Ferric Chloride. I recon that it works even thou it's not heated to 40-50°C.

The construction of an agitating device is starting to form in my head...

How do you get rid of your etchant?
 

Wendy

Joined Mar 24, 2008
23,415
I use around a cup and a half, total, sometimes less. I use a sponge to wipe the board while etching to move it along, it is quite fast (about 3 minutes), but the board is lightly immersed. I throw the sponge part (I cut it off a larger mass) away in the trash, and and dispose of the etchant in the grass.

The receipt is very cheap, 1 part muriatic acid and 2 parts hydrogen peroxide. Both are both very inexpensive chemicals. I'm still using the 1st gallon of muriatic acid I bought after 10 boards, with the 1 gallon container less than ½ used. The mixture self heats quite warm when you mix them, always pour acid into the H2O2, it can splash around otherwise.

I'm still tweaking my process, next batch of boards I make is going to have baking soda in the rinse to neutralize the acid. I'm going to try acrylic clear Krylon spray paint as a non conformal coating to see how well it works, someone recommended it on another site.

I'm also trying baking soda to see if I can keep the fumes under control while storing it.
 
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