Electronic Gold Paste Reclamation???

[MassGoldSmith]

from a company called EMCA ... since purchased by a larger company. The jars are 50 gms with p/n Au 6360-1B. Was used I'm told for thick film on ceramic applications.



Anyone have any ideas on purity or content??? Refining methods????

 

[goldsilverpro]

A company I worked for sold these PM thick film pastes - commonly, gold for the conductors (traces) and bonding pads for mounting chips, platinum for conductors, and ruthenium (as an oxide, I seem to remember) for resistors. They were applied to the thin alumina substrate by silk-screening (actually, stainless steel screen was used) technology and then were fired in a conveyorized furnace, at high temp, to bond the PM to the substrate and to drive off the solvents and binders in the paste. Both the pastes and the alumina contained about 5% (I think), by weight, glass powder (called a glass frit). When fired, the glass melted and bonded the gold to the alumina. They were used to form hybrid circuits, which were then usually mounted, wired, and sealed in hybrid packages.

Since we sold these pastes for another manufacturer, I never knew exactly what was in them but, in the case of gold pastes, I think it was only gold powder, a glass frit, and a blend of solvents and organic binders. I didn't process much of the paste, itself, but I think we just incinerated it at a fairly high temperature and then went through an aqua regia process. I don't know what the solvents, etc., are, but the incineration products could very well be toxic and I would use great caution.

Another approach might be to first leach out the solvents and binders with another solvent, such as zylol, acetone, etc., and then put the dry residue into aqua regia. However, the use of these solvents poses dangers. Also, unless you find the perfect solvent or blend of solvents, the leaching could very well be incomplete.

I seem to remember experimenting with putting the paste directly into aqua regia, with no pre-treatment. I think I ended up with a gunky mess, which created big problems in trying to recover the gold.

Whatever you do, first experiment with small quantities - say, only a gram or two.

Some of these thick film pastes contain no precious metals. An example is the moly-manganese paste used on side-braze packages, for the leg mounting pads, the internal traces, and the wire bonding fingers.

If anyone finds ruthenium paste, I would not try to process it unless you really know what you're doing and have experience in working with ruthenium. Too many inherent dangers.

Maybe someone else will chime in on this subject.

 

[MassGoldSmith]

Sounds exactly like what I'm being presented with......they seem to think it is extremely pure in content, which would be great.

Thanks for your input and help.

 

[goldsilverpro]

The gold in the paste is very pure. However, the glass frit and the solvents, etc., could greatly lower the total gold percentage of the paste.

Is the 50 grams the gold weight or the total weight of the paste? If the latter, the gold content could be considerably less. It might be spelled out on the jar label.

In my experience, these jars are always sealed when new. If the seal is broken, you really don't know exactly what is in them.

 

[samuel-a]

MassGoldSmith

Recently, i had the privilege to work with couple of ounces of thick film pastes, both gold and palladium.
The solvant/binders or what ever organic matter that is in there have a very distinctive aromatic smell to it, almost addictive.

The metals are very pure in these pastes unless stated otherwise on the lable.
No chmicals, the paste was placed in a melting dish, incinirated and then melted under a fume hood. Quite sooty at first, but with temp' it's all gone.

The loss, if i recall correct was 11-12% of weight from start to finished melt product.

 

[goldsilverpro]

The metals are very pure in these pastes unless stated otherwise on the lable.
No chmicals, the paste was placed in a melting dish, incinirated and then melted under a fume hood. Quite sooty at first, but with temp' it's all gone.

That's definitely the best way to do it, Sam. Where was my head? Why didn't I think of that? One of my standard rules has always been, if the metal is pure to start with, don't dissolve it, if at all possible. That applies to stuff like certain Pd contact points and the silver from film.

 

[samuel-a]

The metals are very pure in these pastes unless stated otherwise on the lable.
No chmicals, the paste was placed in a melting dish, incinirated and then melted under a fume hood. Quite sooty at first, but with temp' it's all gone.

That's definitely the best way to do it, Sam. Where was my head? Why didn't I think of that? One of my standard rules has always been, if the metal is pure to start with, don't dissolve it, if at all possible. That applies to stuff like certain Pd contact points and the silver from film.

Somtimes, You can't see the forest for the trees...

Don't beat yourself up Chris.
If it's any consolation... my first hunch on how to deal with this material was same as you. But i got a tip from a very wise man.

This is why i love this forum, different perspectives joined together. makes us all a bit smarter :mrgreen:

 

[samuel-a]

That applies to stuff like certain Pd contact points and the silver from film.

Is there an example of which application one can find pure Pd contacts?

 

[goldsilverpro]

That applies to stuff like certain Pd contact points and the silver from film.

Is there an example of which application one can find pure Pd contacts?

Those tiny rectangular, faceted (half a hexagon, I believe, in cross section), Pd points on old telephone switching station wire relays were pure Pd. We once recovered about 800-1000 oz of pure Pd points from about a 50,000# lot of that relay scrap. I developed a method of dissolving the nickel backing on the points and the closely trimmed copper alloy spring wires the points were attached to, without attacking the Pd. We then sold the points as pure Pd. I applied my own rule in that case.

I've also seen the same points on other items. Someone (jimdoc?) on the forum, way back, showed photos of these same points, at least in appearance, found on certain organs.