Salt Water Etching

[skeeterb]

I saw a post on the electronic labs board, a suggestion to use salt water to etch a PCB instead of the chemicals normally used to etch PCBs. The URL for that post is https://www.electronics-lab.com/forum/index.php?topic=11940.0

 

[ericgibbs]

I saw a post on the electronic labs board, a suggestion to use salt water to etch a PCB instead of the chemicals normally used to etch PCBs. The URL for that post is https://www.electronics-lab.com/forum/index.php?topic=11940.0

hi,
Have you misread the ferric chloride for sodium chloride.???

EDIT: or sodium persulphate.

**broken link removed**

 

[skeeterb]

I'm just posting what I saw in the post on the other board. Thanks for telling me man. I appreciate the correction. But more importantly, I'm wondering if salt water etching would work for making the circuit boards/

 

[Blueteeth]

Yeah it works...sort of.

Tried it a few days ago just out of curiosity. Its just plain old electrolysis, plating some metal by taking the copper of the board. It relies on the copper to be removed to be carrying current, so of course, once a copper area is 'disconnected' from the rest (which is on the +V side) it stops reacting. I did have quite a bit of success in removing a large area around my design, but of course isolated areas, and small traces were left untouched.

So just to say, it does work, but not very well. I used a 12V PSU with a salturated salt solution, it drew a current of 1A. Still took ages. And any immpurities in the solution/electrodes will be effected too, which can ruin the process. So I guess its a carbon electrode for the cathode, pure salt, and a half decent power source.

Addiditonally, this has been used to reduce the amount of ferric chloride needed when etching, also speeds it up. You 'pre-etch' with the salt water method, removing a fair bit of copper, then finish it off with ferric chloride to do the fine bits/isolated areas. Watch out for chlorine and hydrogen though..with a huge powersupply it'll bubble, and we all know what happens when H2 comes into contact with Chlorine. (HCL -> water = hydrochloric acid).

I say try it yourself. As long as you score lines in the board to electrically isolate areas, they should stay intact.

Blueteeth

 

[skeeterb]

hrmm, I wonder if replacing NaCL with NaOH would work, since Sodium Hydroxide is a kind of salt. That way instead of Chlorine gas coming off the one side of the cell, it would be Oxygen, but that may cause a problem in a way, since oxidation is the enemy when it comes to any electronic application. Tell me what y'all think

 

[Nigel Goodwin]

Tell me what y'all think

I think you should use proper etching solution, and stop reading rubbish from electronic-labs!

 

[mvs sarma]

hrmm, I wonder if replacing NaCL with NaOH would work, since Sodium Hydroxide is a kind of salt. That way instead of Chlorine gas coming off the one side of the cell, it would be Oxygen, but that may cause a problem in a way, since oxidation is the enemy when it comes to any electronic application. Tell me what y'all think

If you are desirous of newer methods than what industry uses, instead of "wondering if....", better try and etch a board as per guidelines given at the said post. if it worked, fine, otherwise , you learn a bit. As already replied by Blueteeth, it is nothing more than electrolysis.

 

[skeeterb]

I'm new to designing and building my own circuits, but I have got that one circuit design under my belt. It took a while and a lot of help, but I got it designed as I was seeing it in my head when I started working on it.

 

[jpanhalt]

Chemelec, an active menber of this forum, has a procedure for electroetching. See: **broken link removed**

As for chemical etching, the the chloride ion (or similar) is important in the non-peroxy methods. NaOH alone will not work. John

 

[Glyph]

hrmm, I wonder if replacing NaCL with NaOH would work, since Sodium Hydroxide is a kind of salt. That way instead of Chlorine gas coming off the one side of the cell, it would be Oxygen, but that may cause a problem in a way, since oxidation is the enemy when it comes to any electronic application. Tell me what y'all think

Good to see you're thinking, but sodium hydroxide is not a good idea. The hydroxide will raise the pH of the solution and this will cause copper hydroxide to precipitate out as you etch. The insoluble copper hydroxide will disrupt the flow of solvent to the copper surface and give you an uneven etch. If it adheres really hard it might even stop further etching (although i'm not 100% sure of that).

If you're really hell-bent on avoiding chlorine gas then use sulfuric acid solution instead of NaCl. Sulfuric acid (also known as battery acid) will keep the pH low avoiding the hydroxide problems. sulfuric acid itself though is corrosive so you might want to avoid getting it on your hands. Although now you've traded one problem for another: toxic gas vs. corrosive solution

 

[mvs sarma]

Perhaps non chemical solution is Computer aided milling machine to follow the artwork and produce a PCB within less than an hour.
Elektor magazine of UK, has published a design and they sell it as kit. No more chemicals.

 

[skeeterb]

Good to see you're thinking, but sodium hydroxide is not a good idea. The hydroxide will raise the pH of the solution and this will cause copper hydroxide to precipitate out as you etch. The insoluble copper hydroxide will disrupt the flow of solvent to the copper surface and give you an uneven etch. If it adheres really hard it might even stop further etching (although i'm not 100% sure of that).

If you're really hell-bent on avoiding chlorine gas then use sulfuric acid solution instead of NaCl. Sulfuric acid (also known as battery acid) will keep the pH low avoiding the hydroxide problems. sulfuric acid itself though is corrosive so you might want to avoid getting it on your hands. Although now you've traded one problem for another: toxic gas vs. corrosive solution

I live in a rural community, so its a little harder to get access to some of the chemicals that you use to etch PCBs. Also the three nearest towns doesn't have any places that sell those chemicals that I know of. I'm looking for the cheapest and easiest method of etching a PCB without using any of those chemicals. Since battery acid is plentiful wherever you have a bunch of batteries, so I could use sulfuric acid.

 

[Glyph]

If you want to just use household chemicals for etching then you can use the sulfuric acid electrolysis to get the bulk of the copper off the board.

Once that is gone and you need a further "scrubbing" etch you can then mix sulfuric acid and hydrogen peroxide to create a solution that will etch the rest directly without electrolysis. This solution only keeps for a few hours so you'll need to use it up soon after mixing, so only mix the amount you'll need. If you're mixing straight conentrated sulfuric acid with water the solution will get VERY hot, so do it slowly and carefully. If you're using battery acid that has already been diluted then heating wont be as a big a problem.

The peroxide/acid etch is very weak and i'm only reccomending it if you have NO other choices. its not good for a total etch because unless you can get your hands on 98% sulfuric acid and 30% hydrogen peroxide (drug stores only sell 3%) you won't be able to make a strong enough solution to etch the bulk copper in a reasonable amount of time (you'll be burning plenty of $$$ making baths to keep etching every few hours until its done). Thus the electrolytic etch is a cheaper primary etch and this solution is for scrubbing etch.

If you can get your hands on hydrochloric acid then you might be able to make yourself a cupric chloride etch etch solution. Nasty stuff that smells bad, corrosive, and stains but very easy to make once you have hydrochloric acid. You can find lots of information on it in google, look up "cupric chloride etch".

 

[3v0]

We have been down this road a number of times.

Unless you plan to do a lot of etching safer chemicals such as sodium persulphate are worth looking at.

 

[Glyph]

come to think of it. maybe someone should make a sticky on PCB etching, both commerical products and homemade.

 

[ericgibbs]

come to think of it. maybe someone should make a sticky on PCB etching, both commerical products and homemade.

hi,
Just Googling brought up a number of sites.

This first one looks OK.
http://www.instructables.com/id/Mostly-easy-PCB-manufacture/

**broken link removed**

http://www.youritronics.com/diy-printed-circuit-board-using-photo-etching-method/

 

[jpanhalt]

The peroxide/acid etch is very weak and i'm only reccomending it if you have NO other choices. its not good for a total etch because unless you can get your hands on 98% sulfuric acid and 30% hydrogen peroxide (drug stores only sell 3%) you won't be able to make a strong enough solution to etch the bulk copper in a reasonable amount of time (you'll be burning plenty of $$$ making baths to keep etching every few hours until its done). Thus the electrolytic etch is a cheaper primary etch and this solution is for scrubbing etch.

Just an FYI re: hydrogen peroxide. Clairol (Proctor and Gamble) has a hair "developer" called Clairoxide Clear Developer 40 volume. The beauty store said it was 40% (which sounded suspicious to me); the P&G MSDS implies it is 12%.

That is still a lot stronger than 3%. You have to read the bottle carefully, as there are two almost identically labeled products. One is plain developer and has a variety of waxes, surfactants, and "stabilizers" in it. The other, which is called Clear Developer, is just water and hydrogen peroxide as best as I can find out. It is water clear and odorless. I could not find the MSDS for the clear product on the P&G site. For the other version, it gives the concentration as 12%: https://www.electro-tech-online.com/custompdfs/2008/05/Clairoxide_Developers_30_and_40_Volumes.pdf

For those using peroxide, it might be worth a try, if yo need a higher concentration. I tried some and it certainly seems to be just water and peroxide.

John

 

[skeeterb]

What percentage of acid is the Sulfuric Acid that is found in batteries? If you get the acid out of batteries, you would have to somehow purify the acid removing all the impurities and such to use it. I know a little basic chemistry and know the formulas for calculating chemical compositions, cause I still have my chemistry book from back when I was in Community College.

 

[Glyph]

You'll need to get the acid out of Lead-acid batteries (car batteries and UPS devices) which is sulfuric acid. Household batteries (AA,C, etc.) don't use sulfuric acid.

The acid that comes out of a fully charged lead acid battery 33%. If the battery is dead its usually much lower and full of lead contaminants.

Lead is nasty stuff (liver damage, brain damage...) so it might be better if you can get your battery acid seperately. Auto-parts stores usually sell battery acid seperately for filling dry-charge batteries or replenishing used batteries.

Battery acid in this fashion is still at 33% but its much cleaner, no nasty contaminants, just 33% acid and 67% water.

I don't reccomend further concentrating the acid unless you know EXACTLY what you are doing. 33% acid is dangerous enough as is. When you mix the hydrogen peroxide with it there will be less heating because of the water already present. 98% acid will heat up alot when you add the peroxide, might even boil and splatter acid on you.

If you're just using the acid for electrolytic etching then there is no need to further concentrate. In fact you might even need to dilute it somewhat.

If you need to concentrate further, for some unknown reason, you just have to heat the acid until it boils. When you see the acid form white fumes instead of steam (the appearance is very distinctive, you'll know what i mean when you see it) then you'll have 98% pure acid remaining. further heating just evaporates it so you won't get above 98%.

It goes without saying that acid vapors does WONDERS to lungs and human flesh (think Indiana jones and raiders of the lost ark). You need to do this outside while standing upwind of your setup.

Although when you get down to it: that kind of danger just to etch a circuit board? Unless you're in antartica there has got to be a way to get PCB etching chemicals shipped to you. Might be expensive, but far less risky.

If an extra $20 keeps my flesh on my bones then i'm all for it.