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[TCML] plating



These days, where you can get thin metal films evaporated on fairly cheaply, the cost of the metal is not a big driver, so you can choose for appearance..

Conventional plating is tricky on copper. For instance, surface prep is really, really important, and you can't plate silver or gold directly onto copper, unless you want it to diffuse into the copper. Typically, they do a "nickel flash" first, and plate over the nickle.

Nickle shines up nice, but does discolor with time.

Gold looks nice, and doesn't tarnish. Silver is popular in RF performance applications, because silver is a great conductor AND the tarnish products don't have bad properties (AgO is a decent conductor, for instance). But you'll never keep silver looking good, even if you lacquer it.. (the lacquer is permeable to ions to a certain extent, so eventually, it tarnishes under the lacquer).

OTOH, I'm always running across gold plated junk (spare chassis for equipment, boxes, etc.) at work (JPL) from 20-30 years ago, and it looks nice and yellow. (We plate things with gold for spaceflight because it doesn't tarnish, it's solder-to-able, it has good thermal properties (emissivity/absorption), and it doesn't form a surface layer like aluminum, copper, or silver... ). There's not a lot of gold content there, although it does lead to all those questions about "gold plated electronics".



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