Can just HCL10% dissolve the gold of cpu pins?

[BushidoJSB]

Hi Team - (I've been lurking for quite a long time - I've read lots of Hoke and lots of threads on the forum inc the waste disposal stuff!)

I have 10 black fibre cpus.

The metal heat sync has been removed from the top.

Then the black epoxy middle has been removed using a chisel and hammer and put to one side for processing later.

To remove the tin solder which was holding the metal heat sync on top, I've put them in a beaker with some HCL10% and put on a very low heat - about 55deg C for about 2.5hrs.

Now the gold colour from the pins has gone, and also from the exposed area in the centre where the middle was removed.

I had thought that HCL alone could not dissolve gold (without H2O2 or NaOCl or NaNO3)???

I don't think the gold has flaked off because I cannot see any small flakes at the bottom of the beaker - so has it dissolved, or has something else covered it up making it look like it is gone?

Either way, what should I now do next? - I had planned to use poor man's AR to dissolve the gold...

Many thanks - John.

 

[Yggdrasil]

Hi Team - (I've been lurking for quite a long time - I've read lots of Hoke and lots of threads on the forum inc the waste disposal stuff!)

I have 10 black fibre cpus.

The metal heat sync has been removed from the top.

Then the black epoxy middle has been removed using a chisel and hammer and put to one side for processing later.

To remove the tin solder which was holding the metal heat sync on top, I've put them in a beaker with some HCL10% and put on a very low heat - about 55deg C for about 2.5hrs.

Now the gold colour from the pins has gone, and also from the exposed area in the centre where the middle was removed.

I had thought that HCL alone could not dissolve gold (without H2O2 or NaOCl or NaNO3)???

I don't think the gold has flaked off because I cannot see any small flakes at the bottom of the beaker - so has it dissolved, or has something else covered it up making it look like it is gone?

Either way, what should I now do next? - I had planned to use poor man's AR to dissolve the gold...

Many thanks - John.

Welcome to us.
No HCl alone will do it.

What happens from time to time is that the dissolved Tin cements back on the pins and other metal surfaces.

I have not found out decisively, but what I think is happening,
is that the Nickel/Copper under the Gold plating sets up a cell that makes the Tin cement out.
Gold can not cement Tin.

Just continue and it will clear out.
Or better when the Tin is dissolved just pour off the HCl with the Tin and add fresh for the AP you are going to run?
Your plan was to dissolve the Nickel/Copper layer under the Gold plating right?

Dissolving the Gold and base metals are most of the time not recommended.

 

[BushidoJSB]

Hi Yggdrasil, thank you for your quick reply and your information!

So, tin is soluble in HCL10%, so even though is has maybe cemented back out of solution onto the pins, if I leave it for longer it should redissolve eventually - alternatively, I can replace the (maybe tin saturated) HCL with fresh and then the tin should go back into solution.

Actually I had planned to then move straight to poor man's AR as the next step, as I had understood that residual tin (and metastannic acid) was the main problem and once it was gone moving on the dissolving the gold (and other base metals) would work all ok.

However, you are recommending to to add in an AP step (HCL + H2O2 + copper + bubbler) to make the gold separate from the pins and then use the poor man's AR on just the gold foils ... is that right?

Thank you for the guidance! John.

 

[Yggdrasil]

Hi Yggdrasil, thank you for your quick reply and your information!

So, tin is soluble in HCL10%, so even though is has maybe cemented back out of solution onto the pins, if I leave it for longer it should redissolve eventually - alternatively, I can replace the (maybe tin saturated) HCL with fresh and then the tin should go back into solution.

Actually I had planned to then move straight to poor man's AR as the next step, as I had understood that residual tin (and metastannic acid) was the main problem and once it was gone moving on the dissolving the gold (and other base metals) would work all ok.

However, you are recommending to to add in an AP step (HCL + H2O2 + copper + bubbler) to make the gold separate from the pins and then use the poor man's AR on just the gold foils ... is that right?

Thank you for the guidance! John.

Give it some time.

Often I have not bothered with the Tin since I do not use Nitric on foils.

You do not need the Peroxide.
Just find some green Copper and add to some HCl and start bubbling air through it.

 

[Proffshuggarn]

HCL10%

Sorry to jump into the discussion.
-If I'm not mistaken, @BushidoJSB is wondering if a concentration of 10% hydrochloric acid is useful for the purpose, something I also wonder when I accidentally bought 25 liters of 10% Hcl.
-Or is a higher concentration of 35% hydrochloric acid the only thing that will work for AR etcetera?
-Can the concentration be increased by evaporation?
Sorry to interrupt the discussion. /Dennis

 

[Yggdrasil]

Sorry to jump into the discussion.
-If I'm not mistaken, @BushidoJSB is wondering if a concentration of 10% hydrochloric acid is useful for the purpose, something I also wonder when I accidentally bought 25 liters of 10% Hcl.
-Or is a higher concentration of 35% hydrochloric acid the only thing that will work for AR etcetera?
-Can the concentration be increased by evaporation?
Sorry to interrupt the discussion. /Dennis

It is useful yes.
And since the azeotrope is around 21% it can easily be concentrated to 21%.
Any strength can be used for general refining but for some of the more challenging metals like some of the PGMs one need full strength.

 

[Proffshuggarn]

It is useful yes.
And since the azeotrope is around 21% it can easily be concentrated to 21%.
Any strength can be used for general refining but for some of the more challenging metals like some of the PGMs one need full strength.

Thanks @Yggdrasil

 

[haveagojoe]

wondering if a concentration of 10% hydrochloric acid is useful

10% is the maximum strength available without a licence here in the UK, I use it for my Copper Chloride etches all the time and it's perfectly fine, in fact I think it's arguably better to use lower strength HCl for safety reasons.

It should be fine for AR too, but since I only work with escrap, and since Nitric is not available here at all without a licence, like Yggdrasil I don't use AR for my foils. HCl and pool chlorine tablets is easier to work with anyway- it can be done cold, the fumes are less aggressively noxious and it has the bonus of avoiding the formation of metastannic acid with any tin which may be present. 10% HCl works fine for this too.
As Yggdrasil says, it's possible to concentrate HCl to around 20% by gently simmering but I haven't ever felt the need to do so.