Choosing etchant for bubble tanks

[camerart]

Hi,

I've just made a bubble tank for etching circuits, including heating element.

I am about to etch a double sided PCB with tracks that pass between DIP Chip pins.

In the past I've used Ferric chloride and Sodium Persulphate/sodium Bisulphate. I found the Ferric Chloride a bit dark and stains my old tank, making it difficult to monitor the etching results. The sodium Persulphate mix is clean, and from memory I didn't get good results, but I'm willing to try again. Is anyone who uses bubble tanks got their favourite etchant? or are there any suggestions for a good etchant please?

Camerart.

 

[jpanhalt]

I had poor luck with sodium persulfate too. I use either ferric chloride or cupric chloride (aka copper(II) chloride). Either works fine with a bubbler; although, I usually use the bubbler to rejuvenate the copper chloride, not for etching.

John

 

[mvs sarma]

Some people also use HCl and H2O2 mixture in the industry. they use bubble tank while etching.

 

[camerart]

I had poor luck with sodium persulfate too. I use either ferric chloride or cupric chloride (aka copper(II) chloride). Either works fine with a bubbler; although, I usually use the bubbler to rejuvenate the copper chloride, not for etching.

John

Hi John,

Can you explain the sentence "I usually use the bubbler to rejuvenate the copper chloride, not for etching." please.

C

 

[camerart]

Hi,

I only etch a small amounts of boards. Some of the more industrial mixtures tend to have a flow through, so might not suit me.

I have been looking at the many chemicals and recipes, and notice that some of the chemicals get clouded/exhausted by copper. I wonder if the copper could be removed by putting a charge though it, and copper coating something. Would this work to remove the copper and replenish it? (I doubt it, but the thought appeared)

C

 

[jpanhalt]

@#4 See this discussion: https://jimlaurwilliams.org/projects/seychellePaper/ Also check out the pdf attached. Cupric chloride is very good and completely reusable. Ferric chloride is also reusable, as the iron is not consumed, but in time and after a LOT of etching, the ferric chloride bath becomes a cupric chloride bath. You need to reoxidize the iron or copper, and there are various ways to do that. Bubbling air is the easiest. Ozone or chlorine are faster, and chlorine bleach ends up adding additional alkali and sodium. Chlorine is not really practical for home use. I thought of using an ozone generator, then decided I didn't etch enough plates for that to be necessary. The cupric chloride batch can do plenty of plates between rejuvenation.

@#5 I believe chemelec has a post somewhere describing his pre-etching electrolysis method. The answer is that so long as the tracts are connected together or in some other way other to the electrode, you can plate away the copper and end up having only a very small amount to remove by etching.

John

 

[camerart]

@#4 See this discussion: https://jimlaurwilliams.org/projects/seychellePaper/ Also check out the pdf attached. Cupric chloride is very good and completely reusable. Ferric chloride is also reusable, as the iron is not consumed, but in time and after a LOT of etching, the ferric chloride bath becomes a cupric chloride bath. You need to reoxidize the iron or copper, and there are various ways to do that. Bubbling air is the easiest. Ozone or chlorine are faster, and chlorine bleach ends up adding additional alkali and sodium. Chlorine is not really practical for home use. I thought of using an ozone generator, then decided I didn't etch enough plates for that to be necessary. The cupric chloride batch can do plenty of plates between rejuvenation.

@#5 I believe chemelec has a post somewhere describing his pre-etching electrolysis method. The answer is that so long as the tracts are connected together or in some other way other to the electrode, you can plate away the copper and end up having only a very small amount to remove by etching.

John

Hi John,

Quite complicated! thanks. Chemistry is quite a big field, and so many choices.

Re the @#5 question: That is a more interesting answer than I expected! I was mainly thinking about regenerating the spent Ferric chloride only, no board in the circuit. (hopefully I understood your answer ok)

Going back to the Sodium persulphate/sodium bisulphate mix. I've read that the bisulphate lowers the PH, I'm wondering if our poor results where because the mix wasn't correct? I have found some left over from the last time I used it, so, I'll try this first and report back. My tank is transparent, and this chemical is fairly clear, for watching the results, and I prefer a clear chemical to Ferric Chloride.

C.

 

[jpanhalt]

The bisulfate etchant would probably work better at a lower pH than at a higher one. I lost interest in the "peroxy" methods, because: 1) The photoresist I was using was attacked; and 2) Ferric chloride or cupric chloride worked well. Chemcut also has a monograph on the quality of etching. Ferric chloride ranks very high and gives the least undercutting as I recall.

The cupric chloride method is not at all complicated. One advantage over ferric chloride is that you have the color with which to judge the need for re-oxidation. Ferric chloride also changes color and becomes muddy, but that change is not as distinct as with cupric chloride. I did find ferric chloride a little easier to use in that it was a little slower (heated to 60°C) and the end-point seemed less critical. That is, I needed to watch the cupric chloride method closer to prevent over etching. The difference is slight.

John

 

[camerart]

The bisulfate etchant would probably work better at a lower pH than at a higher one. I lost interest in the "peroxy" methods, because: 1) The photoresist I was using was attacked; and 2) Ferric chloride or cupric chloride worked well. Chemcut also has a monograph on the quality of etching. Ferric chloride ranks very high and gives the least undercutting as I recall.

The cupric chloride method is not at all complicated. One advantage over ferric chloride is that you have the color with which to judge the need for re-oxidation. Ferric chloride also changes color and becomes muddy, but that change is not as distinct as with cupric chloride. I did find ferric chloride a little easier to use in that it was a little slower (heated to 60°C) and the end-point seemed less critical. That is, I needed to watch the cupric chloride method closer to prevent over etching. The difference is slight.

John

Hi John,

The new tank is to replace my old one, both made of perspex. I used Ferric Chloride in the old one, but it stained, the tank, making it hard to watch the process. This is why I'm trying to find a cleaner alternative. I know other people, simply time the process, and get good results, but I don't think they used as fine tracks as I'm using. I like to watch it to make sure.

C.

 

[jpanhalt]

How fine are the traces you need?

The date and name equate to about 4.5 mil. The trace on the PCB is 24 mil.I used ferric chloride and just pulled it out of the tank at various times. It seems like what you want is something that is clear (e.g., one of the peroxide methods) but has the resolution of ferric chloride.

John

 

[camerart]

Hi John,

That's plenty fine enough, I use mm, so 0.4mm track between the chip pins.

I think it's my lack of skill that makes me want to watch the process, so I can stop it when I want.

So yes, if there is a chemical that acts like Ferric Chloride but cleaner, this would suit me.

First I will use the Sodium persulphate/sodium bisulphate mix, that I dug up, with some old sensitised boards, I also found (I understand they are out of date really) then when I order more chemicals, I'll re-think.

Thanks, Camerart.

 

[Pommie]

I used to use Ferric Chloride but after moving to Australia, I could no longer get it. I now use Ammonium Persulphate and get excellent results. I use nearly boiling water and boards etch in less than 10 minutes. If I let it cool then it takes forever.

Mike.

 

[camerart]

I used to use Ferric Chloride but after moving to Australia, I could no longer get it. I now use Ammonium Persulphate and get excellent results. I use nearly boiling water and boards etch in less than 10 minutes. If I let it cool then it takes forever.

Mike.

Hi Mike,

Is there a sensible reason you can't get it in Australia?

What's the difference between Ammonium and Sodium Persulphate?

As mentioned before, perhaps the Sodium Bisulphate in my mix (with Sodium Persulphate) speeds up the process?

My heater is for fish, so I doubt I can get boiling out of it

C.

 

[mvs sarma]

please help to clarify, I was not into chemistry part as I never studied. But for domestic and hobby use, can we filter and remove the copper residue from the ferric chloride . I find lot of sediment after a few etches . I specifically use lab grade anhydrous powder.

 

[camerart]

please help to clarify, I was not into chemistry part as I never studied. But for domestic and hobby use, can we filter and remove the copper residue from the ferric chloride . I find lot of sediment after a few etches . I specifically use lab grade anhydrous powder.

I think it can be filtered easily, by cloth or perhaps a coffer filter (Not sure if it's too fine, but I carefully stop at the residue when pouring it into the tank.

I was asking earlier if it could be electrolised out by using a charge of electricity and late something.

A friend of mine has a large tank that he hasn't cleaned or replenished for years. He has small numbers of boards.

C

 

[camerart]

I used to use Ferric Chloride but after moving to Australia, I could no longer get it. I now use Ammonium Persulphate and get excellent results. I use nearly boiling water and boards etch in less than 10 minutes. If I let it cool then it takes forever.

Mike.

On my Sodium persulphate/Sodium Bisulphate mix instructions, it says 'Normal etching time 20-30mins @40Degrees Do not exceed 50 DegreesC or the solution will break down'.

I noticed my fish tank heater only goes up to 32Degrees, and I've just broken the test tube trying to change the internals to go higher

C

 

[mvs sarma]

I think it can be filtered easily, by cloth or perhaps a coffer filter (Not sure if it's too fine, but I carefully stop at the residue when pouring it into the tank.

I was asking earlier if it could be electrolised out by using a charge of electricity and late something.

A friend of mine has a large tank that he hasn't cleaned or replenished for years. He has small numbers of boards.

C

thanks.

 

[camerart]

I use a long winded method for my PCB stencils, ending with Lith film. There are easier methods

Expose (On my light box) 10 seconds.
Develop in Sodium Hydroxide (Caustic Soda crystals) 1 min+. While in the chemical watch it till it goes dark red all over. I brush it with a soft brush, till the tracks are clear, then wash while brushing gently.
Etch in Sodium Persulphate/Sodium Bisulphate for approx 20+ mins at <40 >50 Degrees C.

It took many tests to get the last one.

Camerart