Question about Sodium Presulphate to etch PCB

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Andres Rodriguez

New Member
I have used, with some success, Ferric Chloride but I'm tired of ruining shirts with brown spots. Therefore, I will be trying the Sodium Persulphate. I will appreciate any comments, warnings, suggestions, etc. regarding that chemical.
 
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Andrew Cowan

Senior Member
It really needs to be hot to work well (about 40 degrees C).

Stick a the glass of a light bulb (low voltage?) in it if you don't have a heated tank.
 
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kevrus

New Member
I use it with good success. As Andrew says, it needs to be heated, I did read somewhere that it's effect is reduced over 45 deg C. I use a fish tank heater set to 40 deg C with a small air pump for bubble agitation. It turns a very nice blue once the copper starts to dissolve but still remains transparent so the etching progress can be easily monitored.
 
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Dippy

Moderator
I use it in a Mega Bubble etcher at 40oC.

Works fine though not as fast as Ferric Chloride by a long way - takes perhaps 50% longer.
Etch results are very good.
And not as stainy or smelly as ferric chloride.


I don't know of any issues that make it any nastier than Ferric Chloride. You will obviously treat all this sort of stuff with care. Ditto disposal.

Where appropriate, oxalic acid will remove most ferric chloride stains - though obviously it is to be used with great care.
 
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womai

Senior Member
As for warnings, you should never store it in a completely sealed container - since it has a tendency to dissolve and release oxygen over time the container can explode because of rising pressure.

On the good side, it causes less underetching than Ferric Chloride, thus can produce cleaner structures and finer detail.
 
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ylp88

Senior Member
Marmitas said:
I have used, with some success, Ferric Chloride but I'm tired of ruining shirts with brown spots. Therefore, I will be trying the Sodium Persulphate. I will appreciate any comments, warnings, suggestions, etc. regarding that chemical.
Click to expand...
I've come to suspect the etchant for some bleaching stains (odd light-coloured spots) I have on a couple of couple of coloured jumpers, possibly due to it being an oxidising agent. But otherwise quite easy and simple to use.

ylp88
 
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Dippy

Moderator
I'll be interested to see how many of the 'etch warriors' here dispose of the chemicals properly after reading the safety data sheets.
I suspect we'll be bouncing around 0% :)

I find that if you weaken it down Ferric makes great moss killer.
 
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Andres Rodriguez

New Member
Thanks everyone for the info.
kevrus said:
I use it with good success. As Andrew says, it needs to be heated, I did read somewhere that it's effect is reduced over 45 deg C. I use a fish tank heater set to 40 deg C with a small air pump for bubble agitation. It turns a very nice blue once the copper starts to dissolve but still remains transparent so the etching progress can be easily monitored.
Click to expand...
All the aquarim heaters (that I found) have an adjustable thermostat up to 30C. What source of heat do you use?
 
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Dippy

Moderator
Ah, so for a while it'll improve the flow :)

I think all my waste pipes are plastic. PVC or PVCu or something like that.
But anyway, I think it makes a good mixer with Gin.
 
slimplynth

slimplynth

Senior Member
1) Take a photo of your nearest and dearest.

2) Using generic Photo Editing software, make a black and white negative of the pic.

3) Take a piece of metal, roughly the same size of your pic and polish it to as close as possible but not a perfect mirror finish (P1200 SiC grit and 9um Diamond spray or a mechanical method for buffing)

4) Print out the negative image, then photocopy (has to be photocopied as the ink melts when heated)

5) Use an hot plate or some other safe method and get your polished metal hot.

6) Using protective gloves, carefully and firmly apply the photocopy to the metal surface, avoiding any movement that will distort the image. Pressing down will transfer the plastic photocopy ink to the metal surface.

7) Remove paper, allow metal and transferred image to cool.

8) Dip metal in Ferric Chloride, depending on base metal, for a short while (Jethete took literally seconds - try different metals for different effect - Brass looked quite nice but not as much contrast)

9) Rinse after removing and pat dry or use a compressed air line.

10) Wash the metal with a decent solvent to remove the photocopy ink - I used MEK.

11) Voilla - a lovely image to give to your loved ones; a metallic xmas/birthday card.
 
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kevrus

New Member
All the aquarium heaters (that I found) have an adjustable thermostat up to 30C. What source of heat do you use?
Click to expand...
the rubber top on my aquarium heater was fixed with a cable tie so I was able to remove the top and rotate the adjustment screw to the other side of the 'stop', giving me a higher temp range. I then used a thermometer to set up the temperature.

Maybe a picaxe controlled etch tank is in order??
 
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nbw

Senior Member
Hmm, the Sod Pers I use recommends 50-60 deg C, on the side of the container. Wonder if I've been overcooking a few. I've been experimenting with the blue Press n Peel film - someone gave me a pack as a present a while ago so I thought I should use it. It's kind of varied. The results can be a little smudged. I clean the copper really well, have the iron as hot as it will go, no steam, a piece of paper between the film and iron, and sit the iron - applying a bit of pressure - for 2 or 3 minutes. The results aren't as crisp as I'd like. Mycroft suggested glossy paper to reverse-laser print on so I'll give that a go.

For those that also iron-on, I'd be keen to know your thoughts on downward pressure, iron temp, etc and whether any of you do anything radical like clamp between metal plates and bake in the oven.
 
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Dippy

Moderator
I just saw this on Maplin's (and a couple of other) sites re: Sodium Persulphate (persulfate).

"N.B To prevent premature breakdown of the solution, do not operate in excess of 50°C."

I must admit I always thought it was 40; ah well, I can turn my Bubble etcher up a bit now.


Aside:
I also read (MG Chemicals) that Ammonium Chloride can affect some etch resist pen inks, so that's something to keep in the cerebral filing cabinet for the future.


nbw: I've never used press-n-peel but I do know that getting etching good can take a lot of experimentation with the equipment you have. Example: does your iron run hotter than my 50 pence Ebay iron? What do the instructions say about temperature? I have seen many good results with Press n Peel.
 
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nbw

Senior Member
Hi BB: the PnP instructions say 275-325F in the old money. My (ahem, wife's) iron doesn't have a proper temp scale - only off, 1 dot, 2 dots, 3 dots. I've tried it on 2.5 and 3 dots with a bit of annoying smearing, despite various tricks and tips I've found such as pre-heating the board for 15seconds, ironing through a piece of tissue paper with wood under the board, pressing firm but not too firm....
 
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Andrew Cowan

Senior Member
I'm a great fan of the sponge method (with Ferric Chloride). I can etc a board evenly in about 30 seconds. I can't see why it wouldn't work with the sodium stuff, unless it was too hot to hold.

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Dippy

Moderator
You can etch (remove copper) evenly from a board in 30 seconds???
That's fantastic!.
That's quicker than a power drill and sanding disk!
How do I go about this?
 
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Andrew Cowan

Senior Member
Assuming it's a false alarm from my sarcasm detector:

I use warmish ferric chloride, latex gloves and a small piece of sponge (as in the instrucables link in post 20). I then submerge the board in the ferric chloride, and rub the board with a bit of sponge soaked in more ferric chloride. This etches the board very quickly - mixing physical and chemical 'errosion'.

A bit like roto-spray tanks which can do a PCB in around 90 seconds.

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Dippy

Moderator
No, I wasn't being sarcastic.
Just truly amazed. And rubbing doesn't damage thin tracks of resist?
And just warm (not hot) ferric?
Spray and Bubble etchers are pretty warm.
30 seconds? Fantastic.

Well then, a new etcher machine is on the cards.
One that looks like a mini car wash, rotating sponges with FC reservoir.
Bob's yer Uncle - 30 seconds.
Double-sided too.
 
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Andrew Cowan

Senior Member
Dippy - i've never tried it on SMD or small track boards, but I imagine it wouldn't be great.

You need to rub quite hard in order to do it in 30 seconds. Good luck with your mini car wash - have you considered making a PICAXE brushless speed controller and running it at 35000rpm? I'm sure you can get down to the sub-second mark!

A
 
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Mycroft2152

Senior Member
The "sponge" method works best on 0.5 oz copper. That is actually pretty thin, you do have to watch your currents in the traces.

In production, the 0.5 oz copper is actually increased to 1 oz during the plating process for creating vias.

I unknowingly tried the sponge method on 2 oz copper and it took forever. My hand hadn't gotten that tired,..... well in a long time.

Myc
 
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kevrus

New Member
posted by Mycroft2152:
My hand hadn't gotten that tired,..... well in a long time.
Click to expand...
There's always the other hand to take over, but not simultneously as not many have enough room for two hands at the same time :)
 
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nbw

Senior Member
Shucks you guys LOL. I guess the ammonium pers rub might work. You could try a couple of vinyl gloves on top of each other, and if you have the amm pers at 40-50 it wouldn't be so hot you couldn't hold it.
 
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Dippy

Moderator
Sadly, I haven't got a plating process at home :)

I just love the idea of breathing in the etchant vapour as I'm rubbing...

Maybe get an old record player, immerse it in etchant and stick the sponge on the stylus :)

Maybe get a decorating painting roller sponge and stick it on a motor.

or just 99 change hands ;)
 
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mikie_121

Member
Why do people persist with heating etch baths, horrible chemicals and the like. Why not use hydrogen peroxide and hydrochloric acid. It's the cleanest way to make a board. These chemicals are cheap, reasonably safe, clean and EASY. I only wear eye protection to etch.
 
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manie

Senior Member
And if you bubble air through it for a (longish) while, it looses the colour and is rejuvinated, voila.... use again and no disposal problems. You could use an aquarium air pump, but not the dispersing stone, it will probably react with the acid...
 
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Dippy

Moderator
That's interesting. I could have sworn that my old Schoolboy chemistry said that dilute HCl doesn't react with Copper.
Mind you, I'm 40 now so my brain has etched by lager.

Anyay, I'd sooner get Sodium persulphate on my hands, socks, floor than HCl - so I'll stick to that thanks.


I use Sena for developer, cheap s chips and very good and fast.

Manie, so bubbling air through the HCl rejuvenates it? Is that right? How many times can you rejuvenate it? Or does it just lo(o)se it's colour? Is that true? Interesting...
 
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devosbi

New Member
Electronics teacher used to call the stuff "Pepsi Blue" :p

Not as nasty stain wise and not quite as a corrosive / caustic, but be aware that after using the solution multiple times and when it starts to go blue it has a lot of copper in it so avoid getting it on your skin or drinking it or anything :p

Copper is pretty toxic so keep that in mind :)

I've always had much more luck with Sodium Persulphate (Doesn't seem to kill all the copper quite as insanely and i find it better for the more delicate developed boards rather then a simple Daylo pen made circuit) rather then the Ferric Chloride, messy stuff it is.
 
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