The parts passes different processes before plating step such as mechanic process e.g. machining … .
During the machining, for protection of the parts, lubrication will be done on them so the greasy parts come to the plating step.
For plating parts, at first, the plates must be cleaned hence a good adhesion will be formed between substrate and deposition. For this reason, there are different cleaner solutions such as acidic and alkaline solutions. Furthermore some else oranic cleaner are used contain Chloroethylene, Chloride Methylene, … . The recently materials are applied for removing the organic oil and grease. For removing other grease, the acidic and alkaline solution will be used.
The alkaline cleaner contains Sodium salts such as silicate, carbonate, phosphate and sometimes hydroxide, in addition emulsifier, distribution and wetting agents.
The alkaline cleaner is applied in two methods: immersion and electrical.
The concentration of solution depends on the amount of grease also require time for removing the grease which be considered. Except concentration and time, there are two more important cases which effect on the solution performance, they are temperature and agitation. For agitation, normally, mechanic agitation or part movement is recommended. Also filtration can help to agitation, but the air agitation must be avoided because air agitation can move sludge. Furthermore air agitation can make hydrogen bubbles which can lead to brittleness hydrogen. Of course the brittleness hydrogen is more common in electrical cleaner.
The electrical cleaner is divided to three kinds: Anodic, Catholics and periodic reverse.
The Catholics method is generally used for copper, aluminum, brass and their alloys. In this cleaner, the part is cathode and hydrogen gas is formed on it which can remove the contamination from the surface of part also from the angles. If the part is iron, the brittleness hydrogen can be formed so the solution with enough foam must be used to exit the hydrogen gas easily.
In anodic cleaner the part is anode and the oxygen gas is result during reaction. Hear there is no danger of the brittleness hydrogen. This cleaner is usually used for steel and stainless steel.
The periodic reverse method, in spite of high cleaning power rather than anodic and cathode method, but are not common because of high cost.
In PCB industrial, the contamination is usually finger prints and surface oil and the inner of holes are greasy because of drilling. The whole of contamination is removed with acidic and alkaline cleaner and PCB will be prepared for the rest process.