Plys, layers, flashing, sandwich? Yes sounds like a great delay sandwich. Basic note: The vast majority of electronic boards have atleast one metallic layer. This being almost any board that uses through hole define (THM, THD, PGA). The sole exception is rear trace boards.ill Ignore these for now.
Boards are made with two outer layers and a single metal layer in between with a lamination holding it all together. Or in less expensive boards the pcb will be moulded around a small piece of metal taking up minimal internal space. Various etches holes dimples and removed valleys control electrical use. Along with the control components . Most boards have a single layer and the most common metals are copper and nickel. Motherboards and video cards are usually three. And here is where sandwich comes in. Server equipment, high grade video cards, cell phones: and the like. Often use 4 or more layers of, normally, gold layers. Much of this falling into telco class or better despite the large size and reduced component occupation. A 7 layer server board has more gold than many CPUs by volume. Micro tablets (phablets) like the galaxy note series, the Mono Space, the Galaxy mega, all go as cell class due to the gold content plus population. As do TI-8x TI-9x and N-series calculators. For their 4 layers of platinum and layer of gold. N64 and Jaguar cartridges go as telco for their 5 gold layers and gold edge connector. Many Atari 7200 carts get telco for the nickel edge connector 3 silver layers and soldered gold pin rom . This should all help in understanding the class benders. When you've got a sandwich board with copper layers it's still in its basic class. If it's grey/silver in colour there's a chance for an upgrade depending on the layers material and if it's a gold sandwich we're going up!
Copper and nickel are universal. Gold is used where fault tolerance is not practical and it must work at all times. Where fault levelling is not possible or practical. Silver matchs gold's application for less money, slightly sacrificing quality. Palladium is used in very small boards due to its small atomic spacing in finished form. (Don't ask that's chemistry and out of my league). Rhodium is used where environmental tarnishing is an issue for palladium.
Any questions on what materials go where I can try to help. But when you get into the why's I'm not as well versed in chemistry. So I'll do my best to google it properly for you.
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