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Gold is considered the best multimeter probe tip (though disadvantages are that it comes off easily when rubbed and is expensive) since its surface hardly oxidizes when exposed to room-temperature air, but I hear that a pure tungsten surface oxidizes even less.

So, why isn't tungsten-plating used for multimeter (e.g., Fluke) probe tips? One cheap potential option is to use an aluminum core with tungsten plating. The only disadvantage that I can find is that tungsten is more brittle than gold, so I wonder if some tungsten plating might flake off every time I probe something. Or, I wonder, maybe tungsten is much more difficult to plate than gold.

For background, I have a robotic system which cannot dig/scratch probes into metal surfaces well (all I have is about 1 Newton-gram of force over about 1 mm^2), but I want to consistently get less than 0.1 mV contact voltage for a forced 1 mA current. Tunnel oxides thicker than about 1nm seem to prevent this, which I believe limits me to gold and tungsten.

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    \$\begingroup\$ "but I hear" could you please state a source for that? It's very central to your question, yet send surprising! \$\endgroup\$ Mar 13 at 22:48
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    \$\begingroup\$ why is your question about the use of tungsten for the manufacture of probes? ... why are you not asking about the problem you are trying to solve? \$\endgroup\$
    – jsotola
    Mar 13 at 23:12
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    \$\begingroup\$ I'm not trying to sound like a jerk saying this but anytime someone suddenly just has a new idea that comes to their mind, it's very likely that someone else (historically speaking) has already asked themselves that and already experimented with it and made it known to the industry, hence why you'll never find tungsten probes on the market. \$\endgroup\$
    – Colin
    Mar 14 at 0:17
  • \$\begingroup\$ @Colin So, are you basically saying you don't know why, but I should assume there is a reason and therefore not ask why? \$\endgroup\$
    – bobuhito
    Mar 14 at 0:25
  • \$\begingroup\$ @bobuhito Okay fair enough 🙂 But you are correct: I don't know the answer and yes, I don't think it would be unreasonable to assume there's a reason. \$\endgroup\$
    – Colin
    Mar 14 at 0:29

3 Answers 3

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From a very quick, underqualified and curious look into this...

Tungsten is not amenable to the electroless plating process on its own with the technology that is currently available. However, tungsten electroless plating is achievable via the deposition of tungsten-carbide, an extremely hard, diamond-like metal alloy. [source]

So, tungsten itself won't plate a probe, and a solid tungsten probe would be pricy and brittle.

To follow on, the various electrical resistivity for relevant materials is in descending order:

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  • \$\begingroup\$ OK, manufacturability might be the only concern, thanks. Just to be clear, all of those bulk resistivity values are fine for me, it's the surface contact/oxide effect that poses a problem for me. \$\endgroup\$
    – bobuhito
    Mar 13 at 22:57
  • \$\begingroup\$ Solid tungsten probes are used for wafer probing, so it's not that impractical to use. They aren't that brittle, though they are pretty pricy (about $15 per probe in large quantities). \$\endgroup\$
    – Hearth
    Mar 13 at 23:15
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Hard thin coatings do not behave the way you think they do. They protect from abrasion, but not deformation. If your underlying substrate is strong enough to withstand the deformation, then a hard coating will prevent abrasive wear that might alter that shape, but it will not contribute anything to withstanding changes due to deformation.

That means that pointed aluminum probes would be too easily bent, even if tungsten coated. A hard thin coatings provide surface hardness but not structure.

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  • \$\begingroup\$ Ok, though this is kind of a side question to my main question, it sounds like I should have suggested a steel (instead of aluminum) core coated with tungsten. If that's still probably not rigid enough, please comment. Of course, there's probably some other proprietary reason tungsten never gets used in the end like others have suggested, but I just don't know it yet. \$\endgroup\$
    – bobuhito
    Mar 14 at 2:39
  • \$\begingroup\$ @bobuhito Probably just not needed in most cases and the equipment to work with tungsten is more expensive. It's easy enough to make solid tungsten probes if you want them. All you really need is a power drill and abrasive. \$\endgroup\$
    – DKNguyen
    Mar 14 at 2:50
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Tungsten IS used for micromanipulator probes. The fact that it's easy to sharpen is one of the reasons.

A multimeter probe...really, almost anything will do, even something that will oxidize will probably get scrubbed enough for a decent contact.

In my opinion, not a business opportunity although I could be wrong and maybe OP will get rich if he pursues it.

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