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Old 12th January 2007, 01:39 AM   #11
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Default bragging..naw

not bragging either... I've seen enough diasters by diy-ers in industry and out, w/o the humility to know their own limitations...

if you've got such know how and equipment, why not sputter etch the ptfe and then evaporate/rf sputter a silver film onto the activated surface, followed by bonding/plating/whatever a thicker silver layer?

piece of cake, see?

wet processing is messy and has alot of gotchas to be successful...

good luck....
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Old 12th January 2007, 08:52 AM   #12
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In their bulk metal foil resistors whitepaper Vishay claim that sputtered material as used in film resistors creates much more current noise, so it's better to use foil... LOL of course I doubt it would make an audible difference, but then again I don't believe silver makes a difference over copper yet I'm using it...

Also, while I do have vacuum, I don't have a sputtering setup and I doubt I could get a nice flat coat that way. Whereas I have most things for any wet job.

If there were only a way to etch away an existing copper cladding to an exact minimal thickness, then I could plate it easily. I made a batch of silver nitrate just two months ago and would be perfect for the job.
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Old 12th January 2007, 11:50 AM   #13
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Default silver plating

The coating you get from silver nitrate solution is gonna be pretty rough at any significant thickness over maybe 1/2 micron. Most silver baths are based on cyanide chemistry, with small amounts of grain refiners such as "turkey red oil", antimony, etc. added to control the deposit morphology. I guess you could burnish it, but the quality of pc board thickness silver w/o refiners is gonna be lousy.

The sputtered layer is thin, maybe 1/4 micron or so, only serves as a bonding layer followed up with more robust coatings by evaporation or electrodeposition.

Might be able to get an electroless (hydrazine or formaldehyde-reduced) silver film (as used for mirroring, etc) to stick to a stripped copper clad board, who knows... give it a try.

John L.
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Old 12th January 2007, 01:14 PM   #14
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For PTFE, a tie layer resin is often an uncured resin like a phenoxy or polyimide layered in, something that will bond to the activated PTFE surface and the foil under extreme heat and pressure. It's usually pretty thin so it doesn't make an enormous impact on the dielectric properties of the board.

The can o' stuff won't be nearly sufficient to get Teflon to bond a foil layer that will stand up to flexing and heat. You really do need a STRONG free radical source (not to mention a press that will take the resins to a cure state and apply enough pressure), and that means specialized techniques and equipment.

Or you could do what auplater suggests, do a sputtered or CVD conductive layer, then plate it up to the thickness you need.

This is not diy stuff.
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Old 12th January 2007, 01:48 PM   #15
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Can you quantify 'extreme' for the heat and pressure? An order-of-magnitude estimate would be fine.

Actually, they temperature can certainly not be extreme, as PTFE can't withstand more than about 250*C, and under moderate pressure would be deformed at over 200*C.
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Old 12th January 2007, 01:56 PM   #16
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That's why you need a press, to take it well into the region where it's softening. I don't remember the pressures we used (this was some years ago), but it did require hydraulics for a pretty small (6" square) platen.
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Old 12th January 2007, 06:01 PM   #17
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Quote:
Originally posted by SY
That's why you need a press, to take it well into the region where it's softening. I don't remember the pressures we used (this was some years ago), but it did require hydraulics for a pretty small (6" square) platen.
Just remember, Nixie, that PTFE is on the list of beiing pretty darned carcinogenic, basically one of the worst inthe world, when you force it to decomposition. Which part of the whole thing here you are attempting to do, may require exatly that. Plus the chemicals involved are nasty solvents,and highly carcinogenic. Which is why the warnings. Guys working at volatile chemical plants every day, are under less risk than a DIYer messing with this stuff.
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Old 13th January 2007, 02:37 AM   #18
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It's only carcinogenic if you exceed around 250*C, and I'm not going quite that far. Otherwise it's extremely inert. I use PTFE tape to seal the ground glass joints on my labware and it survives distillation of nitric acid without adding anything to the result.

What about using a roller instead of a press? A laser printer fuser roller is easy to reuse for this, adding another metal roller for the bottom as opposed to the rubber one, and replacing the halogen light bulb based heater inside the roller with a higher powered one to reach say 200*C. Hydraulics wouldn't be needed since the roller concentrates the pressure on a small line; instead, it would just take longer to process a board. The only problem I see is that the board may get a bit warped, or the foil torn.

If I dissolve the copper from a copper-clad PTFE board, would the surface be still activated and suitable for bonding, or would it need re-etching of the teflon?
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Old 13th January 2007, 03:33 AM   #19
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Quote:
If I dissolve the copper from a copper-clad PTFE board, would the surface be still activated and suitable for bonding, or would it need re-etching of the teflon?
Interesting idea. I suppose you could even etch it down to a very thin (few hundred angstrom) copper, then build up the silver electrolytically. Auplater, could that work?
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Old 14th January 2007, 08:51 AM   #20
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I can generate high power air plasma. Would that etch the surface in the right way?

Or what about this Teflon bonding kit, is this likely to create a strong enough bond? http://www.usplastic.com/catalog/pro...uct%5Fid=12176
A bit expensive at $73 for only 2-4 square feet...
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