# silicon wafer scrap



## arthur kierski (Apr 10, 2009)

i was looking for computers scraps to buy and came across various silicon wafers scrap offers--i heard of gold wafers from computers(just heard and saw pictures)-----does this silicon scrap have any relations with computers? thanks for any reply


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## meng2k7 (Apr 25, 2009)

hi arthur

ive heard someone in hongkong buys silicon wafers, they are usually recycled to make another product like solar cell modules.


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## arthur kierski (Apr 25, 2009)

thanks meng--it is interessting


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## usernameguy (Jun 5, 2009)

I work in a semiconductor research fab. The Si wafer scrap we throw out would not be worth procssing. There would be a VERY low percent of gold with all the Si and other metals to deal with. remember, we're putting on thicknesses on the order of 1micron layers. I do pick through the small bin of broken and scrap wafers at our facility that have just the gold on then, etch it off and precip, but bulk, this would not be economical. I would estimate MAYBE 10 grams of Au per ton of wafer scrap. Now, our facility is a research facility, so an industrial processing facility may be different, but no doubt you'll still have lots of other metals to deal with if that bothers you. I'm still learning and trying to keep things simple at first


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## AurumShine (Jun 5, 2009)

please see this link about silicon wafer scrap.

http://www-03.ibm.com/press/us/en/pressrelease/22504.wss


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## goldsilverpro (Jun 5, 2009)

usernameguy,

1 micron is 40 millionths of an inch. For a 2" wafer (3.1416 sq.in.) completely coated on the back with 1 micron of gold, the value would be about $1.20, at a $950 mkt. I don't know how thick the wafers are, but my guess is .03". The S.G. of silicon is 2.33 gm/cc. Using these figures, a 2" wafer .03" thick would weigh 3.6 grams. Therefore, unless my math is wrong, those gold backed wafers are worth about $150 per pound. Of course, this whole post assumes the gold is 1 micron thick and the wafer is .03" thick. If the wafer were thinner, the $/# figure would be higher.

I assume the die is gold backed only when it is mounted using Au/Si braze, Therefore, if epoxy mounting were going to be used, the wafer would most probably not be gold backed.

Many moons ago, we processed drums of gold backed wafer scrap from IC manufacturing facilities in Silicon Valley. The gold yields were quite good and the $150/# figure doesn't sound out of line. 

I assume that your figure of 10 gm of Au per ton is for wafer scrap that is mostly not gold backed.


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## usernameguy (Jun 5, 2009)

This is correct. As I mentioned, I work in a research facility, not a process fab. It's worth it to ME to pick through the scrap and pull out the wafers with gold on em, but when comparing to the entire amount of wafers, there's very few my lab throws out that have gold. mostly crystal thin films and various other metals. plus, these are just the wafers that get broken or otherwise. Yeah, I guess I'd be very excited if all the wafers had gold on them. So, without fab experience, I'd just warn to be able to see what you're buying before making any deals.
Thanks for the math though GSP, that actually helps alot. We use 4" wafers, and I was curious to know how much I may be recovering. I should be able to tell better now how efficient my method is for extracting the gold based on the final weight I end up with since I generally know how many scrap wafers I've stripped. 

Hey, GSP, did you see my other post? You were right on with that sulfuric for dropping from the non cyanide pating solution. Thanks a ton for that. I now have access to a cyanide based plating solution and am curious if you think the sulfuric will do the same job? It was beautiful. pure gold sponge. I owe you.
Cheers,
Guy

I read the article posted by the user above, which reminded me most of our wafers thrown out are monitor wafers or are used in the furnaces to ensure even film deposition, so I'd imagine industry is fairly similar, but again, I don't have industrial experience, and it sounds like GSP does have some.


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## goldsilverpro (Jun 5, 2009)

> I now have access to a cyanide based plating solution and am curious if you think the sulfuric will do the same job?



*NO!* If the bath is type (1) below, the cyanide will react with the acid and form hydrogen cyanide gas. It wouldn't take much to kill you. If the bath is type (2), you will precipitate gold cyanide (AuCN) and this will make things much more difficult. 

Do you know the pH of the cyanide bath? There are 2 types of baths that contain potassium gold cyanide (PGC). *(1)* One is alkaline and it's pH will be about 10 or higher. It also contains quite a bit of free potassium cyanide. It is usually straw colored. *(2)* The second is an acid bath with a pH usually somewhere around 4 to 5. It contains no free cyanide but usually contains potassium citrate and citric acid. These 2 act as a buffer to keep the pH fairly constant. The acid bath will usually be light pink or green, but not always.

Find out what the pH is and let me know. Although not absolutely necessary, it would help to know the trade name of the bath. How much solution do you have? What is the color of the solution?


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## usernameguy (Jun 5, 2009)

I'm gonna go look right now. I've not yet even seen it. I do know it's been used VERY little. Thanks a lot man! I'll be right back and let you know.
-Guy


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## usernameguy (Jun 5, 2009)

Hey GSP,
So, it's called Aurall 305. There's about 1-1.5gallons of it, along with a pound or 2 of Aurall 305 conductivity salts (I assume worthless, let me know though if otherwise. the waste disposal guys told us they do not recover gold. Their loss). Looking through the semitransparent bottly it's in I'd give it a semi clear light brown color... maybe I'd call it straw colored. I didnt' have access to a fume hood right now, so I couldn't measure pH firsthand, but the handwritten waste label says pH about 7. Now that we have the brand name, let me know if it's necessary for me to measure the pH firsthand still before you can advise. I'm also curious if you have any idea about potential amount of dissolved gold. It's only been used like TWICE!!

Thanks so much man,
Greg


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## goldsilverpro (Jun 5, 2009)

usernameguy,

I don't know the name but, on the internet, it says it is cyanide based. However, that could mean several things, as I have shown. Try to measure the pH or, better still, try to find the data sheet and/or operating instructions that came with the bath. The pH of 7 thing just doesn't seem right although I do know of a particular bath with a pH of 6. Your bath could be similar.

The data sheet/operating instructions will give the pH and the amount of gold in the bath. The majority of gold plating baths on the market have a gold content of 1 tr.oz./gallon (8.2 gm/liter). There are exceptions to this, but not many.

Aurall 305 was patented by LeaRonal. They were bought by Rohm & Haas and they were bought by Dow Chemical. I can probably get a copy of the technical info from Rohm & Haas but they require filling out a form first, for approval. It would be easier and faster if you could find a copy somewhere in your company's files.

Are the conducting salts (CS) labeled "poison"? If not, the pH could very well be 7 and the CS are probably either a citrate or a phosphate, containing no gold.

I'm thinking. Do you have access to a small rectifier? If so, the simplest and safest way to get the gold may be to plate it out onto a stainless sheet. If you tape the edges and back with plastic tape, you should be able to peel the gold off the stainless and then simply melt it. The gold is pure to start with and will stay that way unless you contaminate it. You won't get 100% of the gold but you should get at least 90-95%. This should work no matter what the bath is composed of. Since the bath is almost new, it should plate great. If you want to try this, let me know and I'll give you more details. Also, on the operating instructions, it should give the operating temperature and the current density (amps per sq.ft.). This info will help if you want to plate the gold out.

The other alternative is to drop the gold with zinc dust. This is more dangerous and you definitely need a fume hood and some additional chemicals. You may also need potassium cyanide, depending on the makeup of the bath. Also, the zinc will contaminate the gold and it will require an aqua regia cycle in order to purify it.


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## usernameguy (Jun 5, 2009)

damn, I didn't realize how good I had it with the cyanide free stuff. That was beautiful. The person in charge of the cyanide bath is gone for the weekend. I'll have to talk to her after the weekend. Thanks again so much. I gotta get going. I'll be in touch.
I think the zinc may be the way to go for me. I can get access to a fume hood, a really good one, just not for the amount of time required to plate it all out, so I may look into this more over the weekend.

Cheers,
Greg


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## usernameguy (Jun 8, 2009)

GSP,
Can you provide me with more info regarding the zinc method of dropping Au for the CN based plating solution? If there's a good thread or link, that'd be great. I really appreciate all your help. I'm not sure I want to take the time to mess with this solution. Maybe I'm just spoiled after the non cyanide based solution.
Thanks!


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## qst42know (Jun 8, 2009)

Check the MSDS sheet. If they don't have one request it. By law it should be available.


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## goldsilverpro (Jun 9, 2009)

usernameguy,

First of all, you need some zinc powder. A pound should be enough to drop 7 to 14 oz of gold. I would suggest using 325 mesh. This guy on Ebay sells it. Don't buy the 5000 mesh or 2500 mesh offered by other sellers - it can ignite under certain conditions.
http://stores.shop.ebay.com/FINE-POWDER-AMERICA__W0QQ_armrsZ1

If the pH of the bath is 7, or so, there is no free cyanide present. To have good success in zincing out all of the gold, you will need to add an ounce/gallon of either potassium or sodium cyanide. If you don't use it, you may have problems getting all the gold out.

You need sodium hydroxide, a bucket, about a 12" long stainless or plastic stirring rod, and filtering equipment. You also need HCl and HNO3.

*SAFETY*. Wear gloves and a full face shield. You mainly don't want to get this stuff in your eyes or mouth. *USE A FUME HOOD, especially in step (9)!*

I would strongly suggest that you try this with a 500 ml sample in a beaker to start with.

(1) Put solution in a 5 gallon plastic bucket. 

(2) Adjust the pH to 12 with sodium hydroxide (NaOH). It won't take much, unless the solution is strongly buffered - which it very well may be. Once the NaOH overcomes the buffer, the pH will rise quickly. When you do the 500 ml sample, keep track of how much NaOH it took and use this as a guide. Try not to use an excess. The more NaOH you add, the more zinc it will take, and, also, the more zinc you will have to get rid of at the end. A slight excess won't hurt. A larger excess will work but you will use more chemicals. A big excess may cause problems in dropping the gold.

(3) *AFTER THE pH IS ADJUSTED TO 12!*, add and dissolve about 1 oz of KCN or NaCN per gallon of solution, with stirring.

(4) Add about 1 or two times as much zinc as you have gold, with good stirring. The zinc tends to clump and I usually add it from one of those small squeeze-type flour sifters to break it up. If you don't break it up, the gold will coat the lump and you will use a lot more zinc.

How to tell when all of the gold is dropped. This is difficult without analyzing it. However, you can get a very good idea by the color of the foam created when stirring and by the indication of excess zinc. 

When adding the zinc, whip up the solution vigorously with the stirrer in order to create a little foam. Before adding the zinc, the foam will probably be light yellow. When the gold is out, the foam should be white. 

Also, when you add zinc, the gold will drop as a dark brown powder. When all the gold is dropped, the excess zinc will not dissolve and will appear as a gray powder mixed with the brown gold powder. I would add zinc until the powder is almost totally gray or, totally gray. You want some excess zinc. Better a little too much than not enough. Don't add way to much, though, or you'll pay the piper in step (9). 

(5) Filter the solution ASAP. Try to get it filtered in a couple of hours, or so. If you wait around too long, the excess zinc can dissolve and then some of the gold can also re-dissolve. When doing large amounts of solution that are too much to quickly filter, you can hang a couple of zinc bars in the solution, allow the gold/zinc powder to settle overnight, siphon off the top solution, and then filter the remaining sludge. The zinc bars prevent the gold from re-dissolving.

(6) Rinse the powder in the filter paper several times with hot tap water. The main purpose is to rinse all the cyanide out.

(7) Put the filter paper (if there is only 1 paper) and powder back into the bucket. The paper will fall apart in the acid and will cause no problems. Actually, it will help since it will act as a filter aid.

(8) Add enough distilled water to cover. 

(9) *UNDER THE HOOD*, add small amounts of nitric acid, in increments, to dissolve the excess zinc powder. The solution will get quite hot. Let each addition work until the reaction slows down considerably. Stir and add a little more nitric. Repeat until an addition of nitric produces no reaction. Doing this under the hood is critical, since any cyanide remaining will react with the acid to produce the deadly hydrogen cyanide gas.

(10) Filter and rinse.

(11) Purify the gold using aqua regia


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## usernameguy (Jun 10, 2009)

Nice. Thanks so much man. You're too generous. I'll have to order the Zinc powder. I'm not sure about the NA or KCN though. Maybe I can come by some. What affect will this have if I leave it out. Will I loose the ability to drop a considerable amount of gold, or are we only talking about 10% or less?
Thanks again so much!


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## goldsilverpro (Jun 10, 2009)

Try a small measured amount without cyanide and see how much gold you recover. Compare the recovery with the gold content on the data sheet. I've had occasional success without using cyanide but usually some hangs up. 

This is what I think happens. The gold in the bath is already in the form of a cyanide complex. When you add zinc, the zinc dissolves and some gold drops. The zinc will dissolve in the NaOH but some gold can still be tied up in a dissolved cyanide complex. With extra cyanide, the zinc replaces the gold in the cyanide complex and all the gold drops out. The dynamics of complex metal solutions are...complex. I may be wrong in my analysis of the situation. Like Harold, I am not a schooled chemist. Maybe Lou can chime in.

Are you sure you don't want to try plating out the gold?


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## usernameguy (Jun 10, 2009)

again, with the plating, my concern is the time I have access to a hood. Also, unless I can just use a simple battery or something, I'd have difficulty coming up with a power supply I could use for it. Then, I'd imagine I'd need to keep adding conducting salts to make sure to get all the Au out which would require attention (time). Now, since I have an outstanding fume hood, would you still say heck no to sulfuric acid? I don't suppose there's any one step solutions to this, huh? With the exception of purifying with AR, etc.


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## goldsilverpro (Jun 11, 2009)

To plate out the gold, I don't see why you need a fume hood. If your company plates gold, surely they have a plating rectifier. A battery charger wouldn't work well for this because the bath probably operates at only 2 to 3 volts - if you tried to plate at 6 or 12 volts, you would probably have a mess. Did you ever find the operating instructions or the technical data sheet for the Aurall bath?

I might mention that the sulfuric method only works for non-cyanide baths containing sodium or potassium gold sulfite, as in the BDT10 bath that you already processed. There are other types of non-cyanide baths where sulfuric won't work - for example, the baths containing ferrocyanide. By the way, BDT stands for Bright, Ductile, and Temperature Resistant. I know this because I was working for Sel-Rex when they first developed the BDT series of gold baths.


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## usernameguy (Jun 11, 2009)

I see. I guess I was spoiled with my first experience. The Iodine etch solution was a bit more complex, but it was so nice to just see pure sponge drop out after adding one chemical. oh, well. alas, I'll look into getting the operating instructions. I'm sure we have them. We do have a rectifier, but it's frequently in use. I suppose I could talk to the person who runs it and see if I could just reserve it for a little while. I have no experience with it, so do you have any idea how long I may need to reserve it to plate it all out? I assume I'll need to check in on it periodically to add salts also, correct? I'll talk to her today. she said she can keep it around for another week before she needs to get rid of it.


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## usernameguy (Jun 11, 2009)

OK. I've obtained a power supply for the weekend, and was told I need to run the process at 2mA/cm2. I guess I'll see what I can come up with. I'll reread what you wrote earlier, but basically, you think I can just plate using a couple pieces of stainless for the electrodes, ehh? I guess it's decided.

Thanks so much


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## usernameguy (Jun 12, 2009)

goldsilverpro said:


> usernameguy,
> 
> I'm thinking. Do you have access to a small rectifier? If so, the simplest and safest way to get the gold may be to plate it out onto a stainless sheet. If you tape the edges and back with plastic tape, you should be able to peel the gold off the stainless and then simply melt it. The gold is pure to start with and will stay that way unless you contaminate it. You won't get 100% of the gold but you should get at least 90-95%. This should work no matter what the bath is composed of. Since the bath is almost new, it should plate great. If you want to try this, let me know and I'll give you more details. Also, on the operating instructions, it should give the operating temperature and the current density (amps per sq.ft.). This info will help if you want to plate the gold out.
> 
> ...


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## goldsilverpro (Jun 12, 2009)

usernameguy,

That's .013 A/sq.in. or about 2 A/sq.ft. These current densities are based on the area of the cathode that is being plated. At 100% efficiency, about 7 grams of gold will plate per amp per hour. Towards the end, the efficiency will probably decrease and you may want to then decrease the current to about half. I would make the anode and cathode about the same size or make the anode a little larger. Stainless is not very conductive, so don't use material that is too thin. I would make the electrode sheets at least 1/16" thick. Use non-magnetic stainless if possible. For the size of your bath, 6" x 6" (.5 sq.ft) electrodes should work fine

The most important thing is the cathode. You want the plating to barely stick enough to stay on the stainless but not stick so tight that you can't peel the gold off. This is done by preparing the cathode. Ideally, soak the clean cathode in nitric acid for a couple of hours and rinse well before using it. This will passivate the stainless and coat it with an oxide layer. If you can't do this, don't over clean the stainless. Use no abrasives that might remove the oxide layer already on the stainless. Just let it soak in a weak dishwashing soap solution for a minute or so, rinse well, and let it completely air dry. I would then wrap plastic tape around all edges and cover the back of the cathode with tape. This will prevent the gold plating from plating in those areas and make the gold hard to peel off. In other words, seal off everything except a square on the face of the cathode. The best tape is 3M plater's tape but you probably don't have that. About the closest thing I can think of is plastic electrician tape.

Ideally, operate the bath at the recommended temperature. If you can't, it will probably still work. The plating might not look as good, but who cares.

I would hang the electrodes facing each other at least 3" or 4" apart. Hang them so the top 1" is out of the solution and that's where you can use alligator clips to clip on from the rectifier. Keep the clips out of the solution. A very clean 1 or 2 gallon bucket, depending on the amount of solution, should work fine. A couple of rods laid across the top of the bucket can be used to secure the wires. Don't allow the anode and cathode to short together or you'll blow the fuse on the rectifier.

Very carefully stir the solution every 15 minutes, or so, and keep an eye on things. You can't just set it and forget it.

This is all much simpler than I've described it and I have assumed that you haven't plated before. Just use common sense

Good luck


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## goldsilverpro (Jun 12, 2009)

I was writing my last post before I saw your last post.



> Prepare for a series of dumb newbie questions. 1.)Is a rectifier just the power supply, or are you referring to the entire set up (electrodes, glass tank, hotplate, etc.?)? How improtant is the operating temp? I found the current density to be 2mA/cm2. Lastly, are there other metal sheets I can use for the electrodes? Does distance between them have an affect? Oh yes, I can grab some capton tape used in vac systems, but does the type of tape I use matter while I'm asking?



1) The rectifier is the power supply. I'm almost positive you'll be able to plate at room temp but I'm not 100% sure. Try it at room temp and see. If it stays on the cathode, it's OK, no matter what it looks like. 
2) stainless is about the only metal that you'll be able to peel off the gold
3) Any tape that won't come loose in the solution


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## usernameguy (Jun 15, 2009)

I couldn't get the rectifier this weekend, so I'm gonna try again this coming weekend. The stainless I got a hold of is the right thicnkess you mentioned, unfortunately, it's the magnetic variety. Do you think this'll pose a significant problem? I'm hoping to not threat it with nitric if it's avoidable. It sounds like you think the native oxide may be sufficient anyway. The concern would just be it may be hard to remove, correct? I could always chemically strip the Au also if it turns to be a problem.


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## usernameguy (Jun 18, 2009)

I'm hoping someone can let me know (preferably before this weekend whether it matters if I use magnetic versus non-magnetic stainless for this plating process GSP has outlined above. I hate to pester him. I'm very grateful for all the information he's provided thus far. VERY generous. I guess it is kind of a labor of love, huh? I kind of get the same "gold fever" from this as from prospecting. With my situation, it's also very similar. Depending on use, I never know hoe much gold I"ll drop from solution, kind of like seeing what you have at the bottom of that pan after you've been working on concentrating it for potentially hours. Never enough for retirement(usually not even a days wages), really just fun to do. successfully. Anyway, about the stainless, anyone know? As I said if I don't hear back, I'll give it a whirl and just etch off if I can't peel. I'd just like to get as much recovery as possible.

Thanks!


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## goldsilverpro (Jun 18, 2009)

I think the magnetic stainless will be OK. The main thing is to not damage the oxide coating. The oxide coating is what makes the stainless, "stainless." If you do remove it, the gold will stick tight to those areas. Abrasion or acids will remove the oxides. You don't want it to stick so tight that it won't peel off. The tape is important. Not only will it prevent the gold from wrapping around the edge or plating on the back, it gives you an place to start the peeling. If you can flex the stainless, it might help pop the gold loose and make the peeling easier. If it does stick, you have nothing to dissolve the gold in without dissolving the stainless.

Good luck!


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## yvonbug (Jun 27, 2009)

I've got a bunch of these silicon wafers that are already cut up for IC's. I got 'em out of a dumpster back in the 80's when dumpster diveing was still OK. I've never processed them because I thought that silicon was going to be a bitch to deal with. I'm not sure, still, how to deal with them.


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## Harold_V (Jun 27, 2009)

To my knowledge, silicon is a non-issue. It isn't a problem with acids, so the rule about not using AR for extraction can well be ignored, assuming there is not a large amount of base metal included. If so, treat the base metal with the appropriate process to eliminate all that can be eliminated, then dissolve the values with AR. Silicon should be easily eliminated in filtration. 

Bottom line, near as I can tell, is the real problem is not silicon, but base metals. I stand to be corrected, and welcome comments from those that understand that which I may not. 

Harold


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## Smitty (Jun 28, 2009)

Yvonbug, finished wafers are comprised of many material, but there is no gold inside the actual production of the wafer. If there is, i've never heard of it. The only gold I know about is when the wafer is ready for mounting, certain chips need gold backing or on bonding pads for the fine leads to connect to. From the picture I can't tell if they have the gold film on the back or if they are just golden in color? Semiconductor fabs are typically using copper and aluminum for there metal steps internally. I would agree with harold for using AR. The amount of metal in the wafer is microns thick, typically measured in angstroms.


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## yvonbug (Jun 28, 2009)

I have a few pics of them close up.View attachment 1
I forgot to add that these are from the 80's. And they are gold on the back. I'm not looking forward to scraping them off the sticky plastic, though. A lot of them are like those little stadiums, but alot are smooth across too.


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## Smitty (Jun 28, 2009)

Very nice pics. I've learned from the guys on this forum not to include base metals in my solutions during refining, but I think I would have to break the rules on this one. Your solution may be tainted with some base metals during recovery and hopefully will be removed on the subsequent refining you will do to improve the quality. I would use 50/50 nitric/water and cook until you think all the base metals can be removed from the batch, wash with hot water until you think it's good enough to dissolve the gold using AR.

let me know how it goes, this is the second time i've dealt with Semiconductor Gold.


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## qst42know (Jun 28, 2009)

This is a complete know nothing question. And my not be safe at all.

Could this solution be evaporated to dryness and incinerated to recover the gold? Or would this release the cyanide?


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## goldsilverpro (Jun 28, 2009)

gst,

I can't grasp what you mean. If you're talking about incinerating cyanide chemicals or solutions, read this.

You might die. The last paragraph on page 10 of this link indicates that the incineration of cyanide salts will release hydrogen cyanide.
http://74.125.95.132/search?q=cache:NlxUFDJdFkcJ:www.atsdr.cdc.gov/toxprofiles/tp8-c5.pdf+cyanide+incineration&cd=8&hl=en&ct=clnk&gl=us


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## qst42know (Jun 28, 2009)

I don't know anything of cyanide that's why I was just asking. 

So hydrogen cyanide gas is liberated by the heat of incineration or by acids.

Good to know. 

Thanks GSP. Qst


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## netseeker (Jul 22, 2009)

I was employed as an equipment technician in a wafer fab until recently so I'm quite familiar with the manufacturing processes used. Scrap silicon wafers are gathered by manufacturing fabs for resale to solar cell manufacturers. This is a recent (the last 3 years) occurrence when solar cell manufacturers really ramped up production and couldn't get the silicon they required. I had worked the last 9 years in the PVD (physical vapor deposition) and we repaired equipment used to sputter a variety of metals including Ta, W, Al, Ti, Co and Cu. We actually did deposit Ni/Pt on wafers although the layer was very thin. The targets used were 10% Pt/90% Ni. Our research fab actually experimented with depositing gold as layer. The PM targets used are very valuable and are carefully monitored. The backside gold layer on wafers actually uses the same type of equipment. If you find whole Si wafers they are the ones the solar cell guys want. I don't think the wafer size matters either.

Robert


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## u0uils08 (Oct 27, 2016)

I just bought 30 5" gold silicon wafers, made by AT&T. I paid $57 for all them. One wafer is 7g. I readed that the gold that is on them is 24k, hoping that it is a good buy. I see two different views about these wafers on this post. After I'm done with them, I will post my findings. It may be a little bit because my wife is in labor.


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## Smack (Oct 27, 2016)

Your new, never processed anything for PM's and want to make money right? Sell them. Look them up on Ebay.


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## GOLDbuyerCA (Oct 27, 2016)

i bought a load, suv full, saved em from being turned into solar cells, sold quite a few , for collectors, teachers, educators, technical people in the biz. at Seaside Oregon swap meet. " i paid to much, i am told " as there is very little gold on the 8 inch wafers, Yet. i have seen assay reports out of Nevada, showing that the wafers, of 2 to 5, to 8 inch, are decimal 58 percent, that is 58/100 of 1 percent by weight. 
some wafers, have two or three layers, of gold, used as heat sinking the circuits etched , by heat removal. and there is chrome, nickle, and titanium, and more.


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