The electroplating process is a process in which metal ions in the plating solution are reduced to metal atoms by electrode reaction under the action of an external electric field, and metal deposition is carried out on the cathode. The following figure (1-2) is a schematic diagram of the electrodeposition process. The completion of the electrodeposition process must go through the following three steps:

Liquid phase mass transfer: the hydrated metal ions or complex ions in the plating solution migrate from the inside of the solution to the electrode interface, and reach the side of the electric double layer solution of the cathode.

Electrochemical reaction: hydrated metal ions or complex ions pass through the electric double layer, and remove the surrounding hydrated molecules or ligand layer, and get electrons from the cathode to generate metal atoms. There are three modes: electromigration, convection and diffusion.

Electrocrystallization: metal atoms diffuse along the metal surface to the crystal growth point, and arrange in the crystal lattice in the state of metal atoms to form a coating.

During electroplating, the above three steps are carried out at the same time, but at different speeds, the slowest
One is called the controlling link of the whole deposition process. Different steps are used as controlling links, and the final electrodeposition results are different.