Precision Microelectronic Shields
Challenge
Recoup precious metals and recycle precision shields used in coatings systems for microelectronics.
Deposition
Gold, Chromium and Copper
Substrate
Stainless Steel
Results
A leading international high-tech industrial group active in advanced microelectronics was looking for a supplier to recycle thick layers of gold, chrome and copper deposited onto stainless steel parts.
We were chosen for this recycle challenge and as a result, became the supplier of choice.
The following available technologies were considered first:
• As explained in other case studies, the cyanides could not be used, because they would not dissolve the gold trapped underneath and\or between the other deposited metals.
• The aqua regia would dissolve the stainless steel precision parts in minutes, so the customer would have to keep buying precision parts;
• Blasting, by different blasting media, would mean consequent extraction (dissolution of metals from the media in liquid chemicals) most probably by the current state of aqua regia. Since the extractions yield huge losses of precious metals, we ruled out this possibility.
• The weaker aqua regia, potassium iodide/iodine, thiourea/sulfuric acid/iron (III) sulfate and some other processes were also ruled out too, because they would not stand-up to reliable large-scale implementation, especially for such thick depositions.
We were ideally looking for a technology that would (i) either peel off or dissolve most of the deposited metals, (ii) preserve the stainless steel precision shields, and was (iii) robust and simple enough to scale-up in-house and potentially at remote locations and by inexperienced staff.
Normally, our patented solution would be our no. 1 choice, but the deposition was (i) really thick (it would take time to dissolve all gold), (ii) the lead-time to return the parts was short, and (iii) there was also a lot of chromium.
Moreover, the chromium was directly deposited onto the surface of stainless steel part as the first layer.
Since the outer layer of stainless steel is its corrosion protectant, called chromium oxide, removing chromium from chromium oxide selectively would mean the same as selectively removing a layer of margarine from butter, leaving the butter untouched.
Our patented solution, typically our Number 1 choice, would dissolve copper and gold and leave the chromium layers and stainless steel intact.
In that case we would only clean the parts partially because the first layer of chromium would stick to the stainless steel and the parts would not be clean.
Having all these challenges and facts in mind, as well as, considering the thickness of the precision parts, we decided not to use the our new solution, but our unique Patent Pending wet etching technology that targets chromium oxide.
Our solution was to dissolve (etch away) the chromium oxide (i.e. the protective layer of stainless steel).
If we were successful, the first layer of chromium and all the gold would peel off. The copper would dissolve during the same technological step, which would help in the release of the gold flakes even more.
Since the chromium oxide protective layer on the stainless steel, has the ability to cure itself by the oxygen coming from the air, we figured the thick precision parts would stay intact.
As shown on our video below, our theoretical expectations turned out to be correct.
Moreover – as shown at 0:31-second mark in the video – the large amount of chromium (dark green color of the solution) was dissolved together with the copper, leaving solid gold flakes.
It is important to note that the chemicals we used did not attack the gold.
The gold flakes were filtered off and re-purified with our patented solutions (i.e. dissolved in our new solution and brought back to solid form from the liquid) to reach 99.99% gold purity.
We managed to stay within the lead-time, and since the technology is simple and straightforward, there were no to insignificant loss of gold, and the customer was highly satisfied with the gold return.