No, no, a million times no. Nickel sounds cheap!
But seriously, there is a big problem with nickel plating and MRI machines. There is nothing in the universe more magnetic than a thin layer of nickel.
Yes, a nickel then gold plated surface solders very very nicely. Gold over copper flash also works well. The copper flash makes a very smooth surface on the copper.
Ah, he has got engaged, and needs a cheap wedding ring. How clever of you to see that from the first.
John
In NMR systems, even copper is too magnetic (ortho or para or something) and wrecks field homogenity. Tiny impurities in a stainless screw can wreck a probe. Even the glass sample holders distort the field. People plate the copper bits with secret stuff to null out most of the effects. After a sample is loaded, a bunch of shim coils (like,
20 or 40 of them) are trimmed to get the magnetic field uniform, to a part in 1e-9 or less, across the volume of interest.Then we apply a gradient pulse, which has to settle to a couple of ppm in 100 usec or so. And *that* causes eddy currents...
John
Yes I did, in fact; I was successful using the oil drop method. It works by covering up the solder pad with oil, and scratching the heck off of the aluminum oxide layer covered by the oil. The Al2O3 layer protects the bulk but also doesn't let the solder attach; it's hard but thin, so you can break it up and the oil prevents reforming (it reforms in milliseconds in air). You have to solder under oil, of course, but a simple engine oil is resistant to soldering temperatures.
Aluminum is actually a cool idea---you can hard-anodize it, making it pretty much any color. Since coloring in anodizing is done by introducing the dye in an etched rough Al surface, I imagine that it should be possible to alter other surface properties besides color (hardness, friction properties, maybe even solderability). I have no first hand knowledge, though.
-- Przemek Klosowski, Ph.D.
FWIW: I just had a gold plating job quoted for some wafer/die probing chucks I'm machining. 5-inch diameter aluminum, plated one side with Cu/Ni/ 0.0001-inch Au. $90 each. About double what it was for a similar job in 2002, so I'm not complaining much.
Steve Noll | The Used Hi Tech Equipment Dealer Directory: |
-- Ahhh... Lord Nelson\'s balls. JF
-- Yellow nickel? Shirley, you jest... Or, perhaps he was feigning platinum. JF
-- dia
Yes, m'aam. Sorry, m'aam.
John
Once one learns the trick, it is easy to solder onto aluminum. But the aluminum very easily alloys to lead solder and can get too thin in that area.
Uses cadmium, fumes are poisionous.
Eddy who? Never met him as we are currently out of touch...
Yes, surface hardness can also be controlled.
Nah, or at least it doesn't have to. Most are zinc-tin alloys, or just pure zinc. You rub it on the hot aluminum, which is hot enough that the oxide layer rubs off with the solder. I've done it myself with U.S. cents- not a real great joint, since cents are 2.5% Cu (makes a brittle alloy).
Regular tin-lead solder can be used, if more aggressive mechanical treatment is applied (um, wirebrush in a tub of molten solder?), or corrosive fluoride fluxes are used.
Not really amenable to electronics...
Ironically, aluminum works nicely in ICs, but that's vaporized. Go figure.
Tim
-- Deep Fryer: A very philosophical monk. Website @
-- Ma\'am JF
I've just had a board made with immersion silver plating. Levelling is inherent in the process and solderability was OK.
Leon
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