Re: Chrome, gold plating, brush plating, vapor deposition
Posted by Owen_Dyneto On 2016/1/23 23:31:38
Many methods for metallizing non-conductive plastic surfaces for electronics, radio frequency shielding, and decorative purposes. I'm probably digressing but.....
Way back when, circuitry from one side of a printed circuit board to the other was accomplished by metallic rivets connecting circuitry on one side to the other until a process called "electroless plating" came along (about 1960), primary patents to Photocircuits Inc. of Glen Cove, L.I. It came to be used not just for circuit boards but for all manner of plating copper (or nickel) on non-conductive substrates. It was a complicated chemical process with about a dozen steps but in essence it consisted of first depositing an adherant "catalyst" of a tin/palladium colloid on the surface. Then the tin was etched away leaving hyperactive palladium. The part was then immersed in an alkaline copper complex with a reducing agent like formaldehyde and the palladium triggered a catalytic reduction that deposited metallic copper on the surface. This layer was sufficiently conductive to then allow thickness to be built if desired using conventional electroplating. A simplification of this came along in the early 1990s which applied a thin layer of adherent carbon black or graphite which was sufficiently conductive itself to allow direct electroplating. One advantage of the carbon black technology was that it could be done selectively on a surface by electrostatic imaging not unlike what a photocopier does. I spent a fair amount of my career in the chemical industry working on such systems.
Lots of early plated automotive interior trim in the 60s and perhaps the 70s was done by this method. Though it was certainly known previously, I'm guessing vacuum metallization probably was the winning technology.
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