The finishing.com Hotline: Serious Education ... plus the most fun you can have in metal finishing. Ted Mooney, Webmaster
What is the number of computers to make one ounce of gold?
Q. I want to recover gold off of old circuit boards by scraping it off, I was wondering, on average, about how many computers is would take to make one ounce of gold? And do refiners buy in ounces or troy ounces, and what is the difference between them?Shane L.
- Waseca, Minnesota, USA
A. I honestly do not know how many computer circuit boards you will need to strip to get one ounce of gold, but then again, I don't know how many fairies fit onto a pinhead. What I do know is that there is very little gold used on circuit boards and it is very difficult to recover. It will take you a lot of effort and leave you with a huge pile of worthless circuit boards that you will have to dispose of. Of course, you can scrape the gold off, but this will introduce other metals that will significantly devalue the gold. Once you have got your "gold" you will need to have it assayed before you can sell it. I would suggest you may be better off spending the time on studying your schoolwork and get prepared for an easier way of making your fortune.
I can, however, tell you about troy ounces and such. All precious metals and gems are handled in troy ounces and one troy ounce is 31.035g, compared with a "normal" ounce of 28.47g.
The troy system originated in the French town of Troyes, where they used a weights system based on 12 ounces to the pound, or 5,760 grains, or 0.3732kg.
R&D practical scientist
Chesham, Bucks, UK
Secrets of Gold Recovery from Electronic Scrap
A. A typical PCI circuit board used today in a personal computer has gold edge connectors that are plated fifty millionths of an inch (0.000050") thick with gold. The finger area (measured and added up for both sides) equals almost exactly one square inch. So, multiply the following conversions to get:
1 sq. inch * .00005 inch * 16.39 cubic cm per cubic inch * 19.3 g per cubic cm * .03222 troy oz per gram * $400 per troy oz = $.20 per board
At this rate it will take a lot of circuit boards to get wealthy.
The conversions I used are:
The density of gold is 19.3 grams per cubic centimeter from the "CRC Handbook of Chemistry & Physics" [link is to info about book at Amazon].
There are 16.39 cubic centimeters in a cubic inch.
$400 per troy ounce is a crude estimate of the current price of gold.
.03222 troy ounces per gram is the inverse (upside down) fraction of the value our friend gave in the previous response, 1 troy oz. per 31.035 grams.John Nelson
retired plater - Leesburg, Virginia
A. Here's another way to estimate gold plated value. You can do it in your head.
Divide the gold market price by 1000. At $400 gold: $400 divided by 1000 = $.40
This, 40 cents, is the approximate value of one square inch of gold plating, 100 microinches thick, at today's market price. This figure is used to calculate the value of items of known thickness.
About the thickest plating used today is on the all gold IC and CPU packages, which is about 40 to 60 microinches - let's say an average of 50, which is half of 100 or .5. On these parts, therefore, the value of the plating is about $.40 times .5 = $.20, or 20 cents per square inch.
Please forgive me, John, but, in my experience as a plater and a refiner, the average gold plating on fingers runs about 15 microinches thick, or a little less. This would make it worth about$.40 times .15 = 6 cents per square inch.Chris Owen
Consultant - Houston, Texas
Thanks Chris. I was also thinking that John's thickness estimate seemed high, and when he noted that he was a retired plater I thought he might be retired for a few years now. I can remember when the usual thickness was 100 microinches and more.
I was often servicing early generation electronic controllers for plating machines in the early seventies, and remember the lack of reliability of tin plated edge connectors, and how relatively "cheap" it seemed to save service calls by gold plating them 100 microinches or more.
The idea of scraping the gold off sounds appealing at first, but when you run the numbers and need to scrape somewhere between 10,000 and 100,000 fingers to get a 1-inch thickness, it gets less appealing.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
I have a small used parts and computer repair shop. I've been collecting motherboards and CPUs for some time. I'm reading up on recovery, especially now that gold is at $700 US. I can't find anywhere the amount (estimated or otherwise) of gold used in production of any CPUs. Wouldn't it be nice to have a listing posted somewhere? (ex. 1 g / 486 DX2-66) Perhaps someone that does recovery knows? :D
hobbyist - St. Petersburg, Florida, U.S.A.
Ted Mooney, P.E. RET
Pine Beach, New Jersey