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I have in front of me a raw PCB. The surface mostly has three colors: dark green, orange-gold and white.

As I understand, the green is resist, the orange-gold is copper, and the white just the silk screen.

I find it surprising the color of the PCB's surface copper is quite different to the color of copper pipes. Please compare the orange-gold of PCBs, and the reddish-orange of copper pipes.

Why does PCB copper look more yellow than copper pipes?

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  • \$\begingroup\$ +1 Nice question & answer by Brian. A while ago (not ordering many PCBs directly) I commented to a colleague I'd got 'free' gold plating from a PCB manufactuer I hadn't used before and he convinced me I was colour blind and it was just copper. \$\endgroup\$ – PeterJ Feb 20 '13 at 12:34
  • \$\begingroup\$ All that glitters is not copper, you know! What you have here is "fool's copper". :) \$\endgroup\$ – Kaz Feb 21 '13 at 0:46
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    \$\begingroup\$ You may look at this wikipedia article for more information. \$\endgroup\$ – Steve Meirowsky Feb 21 '13 at 1:51
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Because that board has been gold plated. Ironically, that saves money; copper tarnishes, and would need expensive cleaning immediately before soldering. And gold on the contact fingers makes for reliable connections. Other platings are possible : tin or silver, and formerly lead-based solder. Scrape some green solder-resist off the earth track and you would see a more reddish metal, though it would take a few months to tarnish to the colour of those pipes.

EDIT : the gold plating on the contact fingers may be a different process (thicker plating, to resist wear) - plating on the board itself will be VERY thin.

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    \$\begingroup\$ The mystery of skin depth article on micrwoaves101 is a very interesting point of what some thing the gold plating can help with. The section The mystery of skin depth - a timeless story is the specific section to read and leads to some entertainment. \$\endgroup\$ – Kortuk Feb 21 '13 at 3:32
  • \$\begingroup\$ really convincing answer to a good question... \$\endgroup\$ – Barath Bushan May 6 '13 at 14:03
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Just for sake of complete information, even if you scrape off the resist to get to the real copper underneath, it will still be pretty goldish. Pure clean copper is a very nice goldish color. The Pipes you see at the store are already in a state of oxidation, giving it the rustier color. Eventually those unsealed pipes will turn a green color.

Copper Oxidation Guide

Essentially, the same thing that happened to the Statue of Liberty. It wasn't meant to be green. Copper Tarnishes, oxidizes, into a Patina. Iron oxidizes into Rust. Aluminum tarnishes, oxidizes into Aluminum Oxide, which seals the Aluminum, and gives it a duller shine. Silver does as well. Raw Gold is not shiny.

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  • \$\begingroup\$ IME fresh copper is pink, old dry copper (e.g. pipes that did not leak) is brown and old damp copper (either outdoors or where a pipe has leaked) gives the green color. Gold OTOH is yellow which is pretty distinct from copper of any age. \$\endgroup\$ – Peter Green Jan 4 '17 at 18:29

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