Electroless plating uses a redox reaction to deposit metal on an object without the passage of an electric current.
Because it allows a constant metal ion concentration to bathe all parts of the object,
it deposits metal evenly along edges, inside holes, and over irregularly shaped objects which
are difficult to plate evenly with electroplating.
Electroless plating is also used to deposit a conductive
surface on a nonconductive object to allow it to be electroplated.
Electroless technologies have been used for many decades.
They involve reduction of a complexed metal using a mild reducing agent, typically formaldehyde. For example, mirrors can be manufactured using this reaction:
R-CHO + 2 [Ag(NH3)2]OH 2 Ag(s) + RCOONH4 + H2O + 3 NH3
where R is an organic group or hydrogen. The reaction deposits a shiny coat of elemental silver on the walls of the container.
Copper can be plated using a similar reaction, by
reducing complexed copper with formaldehyde in alkaline solution. The reaction
is catalyzed by palladium, which is deposited on the surface in extremely small amounts in a previous step.
Nickel is also often plated using electroless processes.
If you examine the reaction above you'll realize that conventional electroless plating isn't exactly a "green" technology.
Chelated metals and formaldehyde in wastes are toxic (formaldehyde is a known carcinogen).
Automata, Inc. has a detailed description of the conventional electroless
copper plating process, including a consideration of emerging techniques to make the process more environmentally friendly.
They note that a move away from conventional electroless technologies is expected in the future due to environmental regulations.
Scientists at Oak Ridge National Laboratory have also developed processes that allow recycling of chemicals used in electroless plating.
Author: Fred Senese firstname.lastname@example.org