BGA RAM Chips cleanup - unexpected results query

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Snapper1

Member
Joined
Oct 7, 2020
Messages
7
Location
Melbourne
Hi Y'all. Another relatively new member here - a total amateur at the recovery and refining processes so taking it very slowly after accumulating quite a bit of material to work on. I have been reading this forum for two to three years while accumulating and taking advice from the forum posts and benefiting greatly from the experience of members contributions over the years. so thank you all for your contributions.

So far in my recovery efforts I have been using the AP Method to recover gold foils from fingers and other surface foils where "clean" access to the foils is not contaminated by solder etc and all that has been very successful - I have built up quite a collection of foils awaiting refining. I have also pyrolysed a bunch of IC's and have the results now waiting next steps after magnetic and gravity separation and that appears to have been a success to this point as I can see quite a lot of tiny gold wires in the bottom of the container along with the remaining junk that you always end up with.

Now I have a few kilos of BGA RAM Chips that I have just started preliminary processing of and have run into unexpected situation. To set the scene the chips had been cleaned up with the solder balls removed (using a small very sharp craft chisel) on all but a few that I kept for experimenting with. My plan was to remove any remaining (I assume something like 80/20) tin/lead solder by soaking in HCL before proceeding to incineration.

I started the processing by putting just 2 of the cleaned chips in about 10ml of HCL and observed the process - after about 10 minutes the HCL started to develop a very light purplish tinge as the solder slowly bubbled off. I thought that a little odd as I was expecting the colour to remain clear, but then add 2 more chips, this time with the solder balls still attached, to the same HCL bath and that slowly cleaned the chips and left the HCL a slightly darker purplish colour, and at that point I noticed that there were a few very small gold flakes floating in the solution. I left it sit overnight and in the morning the solution had turned to a yellow/greenish colour and the small gold flakes were still sitting in the solution as I expected they should be.

Assuming the colour was maybe/possibly/probably related to any contaminates from the chips or possibly from the lead in the solder, and that the gold flakes the result of solder pads that had been released from the disolved solder balls (that had probably come from the solder pads on the board the chips were recovered from) I continued to put more cleaned chips into the same solution after adding about 20ml more HCL. I have since processed about 200gm-250gm of the chips through the same small amount of solution with all chips cleaned very nicely.

Here's my question - the solution has become progressively darker purplish to the point where now it is difficult to see light through, and the amount of gold flakes has slowly built up as more and more chips were run through the solution. Am I right in assuming the colour change/build-up is due to lead from the solder, why did it change back to the yellow/greenish colour overnight, and finally why would gold flakes be released from these chips?

My expectation was that the solution would remain relatively clear as in a stannous chloride solution (unless lead from the solder is the cause which I now assume it must be), and I didn't expect many (if any) more gold flakes to appear in the solution as I was processing "clean" chips.

Your thoughts and experienced input would be greatly appreciated.....

Thanks
Steve
 
Last edited:
Most likely the purple color is colloidal gold from the solder.
When you solder something it is created an alloy of what you solder and the tin.
The pads the chips are soldered to has a thin layer of gold to prevent it oxidizing before the soldering has been done.
Even if the color is strong, it amounts to very little.
The gold foils comes from the soldering pads as well, there are often free pads not used, HCl may dissolve the Nickel under them.
The reason it clears up, may be that they clump up and drop out,
or that the oxygen in the HCl creates enough oxidizing potential to dissolve it.
 
Most likely the purple color is colloidal gold from the solder.
When you solder something it is created an alloy of what you solder and the tin.
The pads the chips are soldered to has a thin layer of gold to prevent it oxidizing before the soldering has been done.
Even if the color is strong, it amounts to very little.
The gold foils comes from the soldering pads as well, there are often free pads not used, HCl may dissolve the Nickel under them.
The reason it clears up, may be that they clump up and drop out,
or that the oxygen in the HCl creates enough oxidizing potential to dissolve it.
Thanks for your reply. From my reading to date trying to recover any colloidal gold in this solution isn't going to be a simple process and probably isn't worth the effort.
Thanks again.
 
Not enough gold to warrant he effort.
Its in the nano or micro grams at best.
 
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