Why is gold plated on high end audio equipment instead of using copper?

[paulhunn]

Hi
I was wondering why high end audio equipment is plated with gold when copper is obviously cheaper and has a lower resistivity. Anyone shed any light on this?

Thanks

Paul

 

[cesiumfrog]

Is it to do with corrosion? It's a real pain when electrical contacts start intermittently failing..

 

[paulhunn]

Is it to do with corrosion? It's a real pain when electrical contacts start intermittently failing..

Hmmm i always thought copper was pretty resistant to corrosion since it's used for water pipes etc and as a plating to an audio jack it's not exactly going to be under particularly harsh conditions.

 

[f95toli]

No, the surface of copper corrodes very quickly when exposed to air; you will in fact ALWAYS have a thin layer of oxide on any copper surface left exposed to the air.
Copper is also very suceptible to corrosion due to e.g. salt water or pollution (or in the case of connectors: sweat); pollution (as far as I remember specifically sulphuric compounds) is why copper roofs turn green after a few years.

However, the good thing about oxides is that they protect the material underneath; this means that once you have a thin layer of oxide the rest of the copper corrodes very slowly. This is why you can use copper pipes for fresh water (although if you've ever looked at a copper pipe you will have noticed that it looks dull, not shiny).
The bad thing about oxide is that it is a very bad conductor, which is why copper is usually plated (usually with gold) when used in connectors.

 

[Anti-Meson]

I believe it is a marketing strategy. Take HDMI cables for example, some are copper plated, some gold, yet they both serve the same purpose. But adding "gold plating" may persuade some people to fork out more money for it, when it does exactly the same as standard cables.

 

[f95toli]

Cables are very different from connectors, once there is an electrical connection in place it doesn't really matter if the copper oxidizes a bit unless you are working with very high frequencies (where the skin depth is so small that the surface resisitivity actually becomes an issue, this is why microwave circuit-boards are often gold plated).

I don't think I've ever seen a "pure copper" connector, even the cheap ones are usually nickel plated.

 

[gnurf]

From the Wikipedia entry on http://en.wikipedia.org/wiki/Gold_plating#Electronics":

Gold plating is often used in electronics, to provide a corrosion-resistant electrically conductive layer on copper, typically in electrical connectors and printed circuit boards.

With direct gold-on-copper plating, the copper atoms tend to diffuse through the gold layer, causing tarnishing of its surface and formation of an oxide and/or sulfide layer.

A layer of a suitable barrier metal, usually nickel, is usually deposited on the copper substrate before the gold plating. The layer of nickel provides mechanical backing for the gold layer, improving its wear resistance. It also reduces the impact of pores present in the gold layer.

 

[paulhunn]

No, the surface of copper corrodes very quickly when exposed to air; you will in fact ALWAYS have a thin layer of oxide on any copper surface left exposed to the air.
Copper is also very suceptible to corrosion due to e.g. salt water or pollution (or in the case of connectors: sweat); pollution (as far as I remember specifically sulphuric compounds) is why copper roofs turn green after a few years.

However, the good thing about oxides is that they protect the material underneath; this means that once you have a thin layer of oxide the rest of the copper corrodes very slowly. This is why you can use copper pipes for fresh water (although if you've ever looked at a copper pipe you will have noticed that it looks dull, not shiny).
The bad thing about oxide is that it is a very bad conductor, which is why copper is usually plated (usually with gold) when used in connectors.

Thanks guys that makes a lot of sense now i think about it.

 

[Born2bwire]

No, the surface of copper corrodes very quickly when exposed to air; you will in fact ALWAYS have a thin layer of oxide on any copper surface left exposed to the air.
Copper is also very suceptible to corrosion due to e.g. salt water or pollution (or in the case of connectors: sweat); pollution (as far as I remember specifically sulphuric compounds) is why copper roofs turn green after a few years.

However, the good thing about oxides is that they protect the material underneath; this means that once you have a thin layer of oxide the rest of the copper corrodes very slowly. This is why you can use copper pipes for fresh water (although if you've ever looked at a copper pipe you will have noticed that it looks dull, not shiny).
The bad thing about oxide is that it is a very bad conductor, which is why copper is usually plated (usually with gold) when used in connectors.

At some point during my studies at UIUC they replaced the gutters on the mathematics building, Altgeld Hall. The gutters were copper and they were replaced by new copper gutters too. It was very interesting to observe how quickly the brilliant new copper gutters oxidize into a dull green patina. I recall it took only a few months before the elements did their work. It was pretty while it lasted though.

Aluminum is another conductor that has a nasty problem of oxidation. Alumina, aluminum oxide, readily builds up on the surface of exposed aluminum and has a very low conductivity compared to the unoxdized aluminum. This also presents a problem when using aluminum wiring although, as f95toli already mentioned, it is usually used at very low frequencies so that much of current flows below the oxide layer.