If silver is the best conductor of electricity, why is gold used in electronics instead?
In: Engineering
It is because silver is much more reactive. Essentially, it rusts. Especially if it is carrying a current. In the case of silver, we call silver rust ‘tarnish’. You don’t want your circuits rusting.
Gold, on the other hand, is darn near inert.
One of the great things about gold is that chemically it is very stable. Under typical conditions, it’s generally quite happy to just sit there and remain gold and not react with much in its environment.
Silver is not as stable. More specifically, it’s likely to tarnish over time, and as it tarnishes it becomes less useful as a conductor. Silver will tarnish from humidity in the air, which is a pretty tough thing to avoid in many potential use cases.
If conductivity matters then copper is the most cost efficient solution. The difference to silver is marginal, so a silver wire can be like 2% thinner for the same resitivity, at a high multiple of the cost.
Gold is used for exposed contacts that shouldn’t corrode
Silver and copper are both better conductors than gold. (With conductivities of 6.30×10^7 S/m, 5.96×10^7 S/m, and 4.10×10^7 S/m respectively.)
However, both silver and copper tarnish when exposed to air, whereas gold does not. That tarnish is oxidized metal, which has far worse conductivity than the pure metal it came from. In the case of pure silver the conductivity is 6.30×10^7 S/m whereas silver oxide has a conductivity of ~1×10^3 S/m; in the case of pure copper the conductivity is 5.96×10^7 S/m whereas copper oxide has a conductivity of ~1×10^1 S/m.
So, the reason that gold plated pins and connectors are used in high-end electronics hardware is because, though they might be worse than brand-new copper or silver connections, they will maintain their performance later on when the silver or copper connectors age and tarnish.
Gold is used because of it’s other physical properties, not just it’s conductivity. Gold doesn’t corrode (oxidize), so it’s commonly used for things that get plugged it – faces of connectors, pins, etc. Most other metals develop an oxide layer which degrades the electrical signal. A secondary use of gold is for connecting silicon to metal using a process called wire bonding.
You can alloy silver until it’s corrosion resistant, like they do in the nuclear industry, but then it’s no longer more conductive than gold.
Solid gold is not used in electronics. Gold is plated onto connectors because of its chemical properties.
Gold isn’t used because it is very conductive, it is used because it resists oxidation so maintains a clean contact. Silver and copper oxidize over time. Aluminum is good enough as a conductor but it’s oxidation is so tough that it is very hard to get a good contact or solder joint. Basically every reason we don’t use aluminum over copper comes down to oxidation
On Earth with oxidation, copper wire is a cheap conductor, and gold is great for contact points.
Electrical engineers use the thinnest (cheapest) gauge of copper wire that also has the ability to bend, flex, and move while also balancing how the copper wire degrades over time. The gold plating is also extremely thin, as cheap as possible while still keeping the non-reactive contact point.
Silver wire is sometimes used in satellites. While it is more expensive than copper and only offers minimal improvements, the cost is less important and the conductivity is more important.
Aluminum wire is both lighter and cheaper than copper making a tradeoff against wearing down and the extra electrical resistance. It is used for very long wires like long distance power lines, and in airplanes for the weight despite being a slightly worse conductor relative to wire thickness. The oxidation issues and costs there are balanced against the other costs, and some industries choose it.
Gold doesnt rust and is very malleable (soft). This makes it ideal for the surface of connectors because it provides a large contact surface that doesn’t separate over time. In general you only need a very thin layer of gold to achieve this effect.
EDIT: since the plating is very thin, the relatively small difference in conductivity isn’t an issue.
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