What is Electroless Deposition
Electroless deposition, also known as electroless plating, is a coating process widely used in the PCB industry. Unlike traditional plating methods that require an external electrical current, electroless deposition allows for the uniform deposition of a metal coating on a substrate without the need for an external power source. This process is particularly advantageous for coating complex geometries, such as cavities and the inside of drilled holes, as it ensures a consistent and even coating thickness across the entire surface.
There are two main mechanisms involved in electroless deposition: immersion processes and electroless processes. Immersion processes are commonly used for plating metals like gold, silver, and tin. In these processes, the material to be coated, if less precious, goes into solution and releases electrons, while the more precious metal ions in the surrounding solution are reduced by absorbing electrons and being deposited on the electrode. This continues until the entire surface of the substrate is covered with a thin layer of the more precious metal. The maximum achievable layer thickness in immersion processes is approximately 0.1 μm.
On the other hand, electroless processes rely on the addition of reduction agents to the electrolyte. The metal deposition occurs through the catalytic influence of the substrate surface, preventing uncontrolled deposition. Palladium-containing solutions are often used for activation, which seed the surfaces with palladium and act as a catalyst in the copper and nickel electrolytes. Electroless processes are primarily used for copper, nickel, and gold deposits.