The preparation step of the metal surface of a manufactured part is the most critical process of electroplating. A properly prepared surface provides an adherent surface for subsequent metal deposits. After a part is manufactured that is to be electroplated, the base metal is typically coated with several layers of soils. These soils may include oxides, scale, lubricants, buffing compounds, rust preventatives, phosphates and handling residues. These soils must be removed to activate the base metal.
There are several factors that need to be considered when preparing metal for plating. First, proper identification of the substrate or base metal is very important. Next, presence of oxides can make pre-treatment difficult. Knowledge and identification of soils is very helpful in planning the preparation process. Lastly, it is important to know the type of finishing that will be applied to the part.
Preparation stages often include pre-cleaning, secondary cleaning and surface activation. Pre-cleaning is often performed by a an immersion/soak cleaning stage. Cleaners high in alkalinity are usually the preference in this stage and the strength of the cleaner is for use is determined by the soils that are to be removed. Concentration of the cleaner, temperature of the bath and degree of agitation are determined based on the difficulty of soil removal. It is in this step, that the bulk of the soils are removed.
Secondary cleaning typically involves one or more steps of electrocleaning. In this process, the remaining traces of microscopic soils are removed. This preparation step is more commonly referred to as a polishing step. Surface activation is often the final step of the preparation process before plating. Activating the base metal surface neutralizes alkali, removes oxides and often etches the surface to create an adherent surface. It is often done with a dilute acidic solution.