Electroless deposition induction period

Steady-state electroless metal deposition at mixed potential is preceded by a non-steady-state period, called the induction period. 

Induction Period. The induction period is defined as the time necessary to reach the mixed potential at which steady-state metal deposition occurs. It is determined in a simple experiment in which a piece of metal is immersed in a solution for electroless deposition of a metal and the potential of the metal is recorded from the time of immersion (or the time of addition of the reducing agent, i.e., time zero) until the steady-state mixed potential is established. A typical recorded curve for the electroless deposition of copper on copper substrate is shown in Figure 8.11. 

Electroless plating. This process involves autocatalyzed decomposition or reduction of a few selected metastable metallic salt complexes on substrate surfaces. The reaction should be carefully controlled to avoid potential decomposition of the metal film thus formed and to control the film thickness. The induction period of the reaction can be appreciable and an effective way of reducing the period is to preseed the substrate in advance with nuclei of the metal to be deposited in an activation solution [Uemiya et al., 1990]. 

The Electroless plating deposition (ELP) technique is based upon the controlled auto-catalyzed decomposition or reduction of meta-stable metallic salt complexes on target surfaces [75]. In the case of palladium, usually, the substrate should be pre-seeded with palladium nuclei in an activation solution in order to reduce the induction period of the autocatalytic plating reaction. For some applications, this technique provides strong benefits such as uniformity of deposits on complex shapes and hardness. Palladium and some of its alloys are among the few metals that can be deposited in this way [11]. However, this method presents some drawbacks such as difficult thickness control, costly losses of palladium in the bath, not guaranteed purity of the deposit and so on [75]. 

---