There are three major mechanisms by which metal ions reach the cathode surface:
- Away from the electrodes, transport within the electrolyte is by fluid movement (‘convection’), so plating baths are kept agitated, which also ensures that the electrolyte temperature is the same throughout the tank.
- There will be a diffusion layer at the interface between cathode and electrolyte, with a concentration gradient of metal ions. In the steady-state situation which is set up, metal ions are replenished at the cathode at exactly the same rate as they are depleted. This layer is usually less than 300 µm thick, and often only 1–50 µm thick.
- Ion migration will contribute to the transport.
The development of laser-enhanced electroplating process offers a promising technique for high-speed and mask-less selective plating and/or as a repair and engineering design change scheme for microcircuits [300, 325-28]. For this, temperature is used to modify the position of the equilibrium potential in a localized region so that electro-deposition is driven by the potential difference between this region and the non-irradiated regions. Use of a focused argon laser beam (488nm) in an acid copper solution provided plating rates as high as 25µm/s . Bindra et al [327, 328] discussed the mechanism of laser-enhanced acid copper plating and Paatsch et al  reported on laser-induced deposition of copper on p-type silicon. It was demonstrated that the increase in the plating rate under laser illumination results principally from photo-induced heating of the electrode surface .