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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?

enter image description here enter image description here

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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, 2013 at 12:34
  • \$\begingroup\$ All that glitters is not copper, you know! What you have here is "fool's copper". :) \$\endgroup\$
    – Kaz
    Feb 21, 2013 at 0:46
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    \$\begingroup\$ You may look at this wikipedia article for more information. \$\endgroup\$
    – Steve Meirowsky
    Feb 21, 2013 at 1:51

3 Answers 3

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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, 2013 at 3:32
  • \$\begingroup\$ really convincing answer to a good question... \$\endgroup\$
    – Barath Bushan
    May 6, 2013 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, 2017 at 18:29
  • \$\begingroup\$ @passerby why not blue (cu2+)? \$\endgroup\$
    – JinSnow
    Sep 14, 2020 at 15:43
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    \$\begingroup\$ My father lived in a big old house in Vermont with a copper roof. At one point he had to have it replaced. Apparently, the day after it was done the daughter of a neighbor got off the school bus, then rushed home, saying, "Mother! Mother! The Beasts have gold roof!" \$\endgroup\$
    – WhatRoughBeast
    Nov 7, 2021 at 22:52
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Unless you specified a gold plating technology, that board is probably OSP: organic solderability protector a.k.a. "organic solder mask", "copper protector" or "preflux".

It's been coated with thin transparent protective layers (often containing some dissolved copper). It's not just a coating: it reacts with the copper substrate to form a locked surface, preventing oxidation. Unlike tin/lead/paladium/gold surface treatments, the organic compound is removed by flux when soldering.

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