nice old boards
- Thread starter floppy
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element47
Well-known member
Boy, that would seem to be the ideal genre of boards for PC PM extraction: No solder mask and the *entire* trace is gold plated vs just the contact fingers. Very nice!
They do look nice dont they. But they aren't pc cards. They are old telcom cards. I don;t know exactly how old but the one has a repair card attched to it thats dated 1975. So I assume that they're atleast older than that. The traces are very thick. I can actually use a knife to peel the edge of one the fingers up and pull the entire trace off. I'm pretty interested to see what kind of yield these will give. If anyone in here has seen these or processed boards similar I sure would be interested to hear about it.
floppy said:
Don't be fooled by the traces. They are only about 1% gold, or less, by weight, if my math is right. A thin layer of gold over a thicker layer of nickel over a thick foil of copper. And then there's the adhesive.
floppy said:
Keeping it simple, most all boards start with a solid foil of copper (attached to the board material with adhesive) that weighs from 28.4 grams (1 av oz) to 56.8 grams (2 av oz) per square foot. Through a series of masking, etching, and plating steps, the copper is etched away from certain areas, nickel and gold [or any other metal(s) desired, such as tin or Sn/Pb solderplate] are plated on top of the copper, and the desired circuitry is formed. In the case of fingers, the nickel is about .0002" to .0005" thick and the gold about .00003" thick. The gold might be thinner than this but will usually not be thicker. There has probably never been a board made with solid gold traces. It would be extremely wasteful.
All you need is enough gold to prevent corrosion to the underlying base metals and/or to be thick enough and hard enough to allow multiple insertions without wearing through the gold layer. Also, in some cases, it must be thick enough to act as an etchant mask. For things such as fingers or connector pins, .00003" of gold (about .0095 grams per square inch) is adequate and this thickness has been used at least since I started in this business in 1966. There are thinner or thicker exceptions but the exceptions don't include solid gold fingers or traces.
In re-doing the math, I came up with the gold percentages on finger traces ranging from about 1.5% to 4%, by weight. Sorry about my error. I'm old and it's late.
element47
Well-known member
"PC" can mean "printed circuit" or "personal computer" when referring to boards; or "politically correct" in other contexts.
got ya element. sorry bout the mix up. And thank you for the explaination GSP. I will definitely dispose of the mercury relays stihl. As for the gold content there still has to be more than just processing the finger contacts alone. Especially out of a few hundred or more.
silversaddle1
Well-known member
Oz said:
Our local landfill will take mercury switches and so forth, no charge.
patnor1011
Well-known member
He can de-solder them and sell on ebay.
I would be reading up on those switches to see if their are any PM's inside, who knows, their could be a nice little chunk of gold inside...
Although the Mercury switches would probably be be a pain to process.
Could one use heat Distillation to process the switches if there was found to be PM's inside worthy of salvation?
Although the Mercury switches would probably be be a pain to process.
Could one use heat Distillation to process the switches if there was found to be PM's inside worthy of salvation?
maltfoudy
Well-known member
if you take the plastic covers off those relays and turn down the little reeds you will see contact points,i have lots of boards simular to the ones pictured and they have gold color points,very small but they are there.
qst42know
Well-known member
patnor1011 said:
I am certain there are shipping regulations against that, with stiff penalties if caught.
patnor1011
Well-known member
qst42know said:
Probably not. You can buy whole range of electronics or part which contain mercury without any problem. He would not ship mercury by kilos only few relays.
