Plastic is used in some industrial such as automotive industrial or decorative application because the Plastic is simple and inexpensive. Plastic is the same PCB in dielectric characterized then for plating the plastic plates they must be electric at first. There are several methods for this reason such as flame and arc spraying, vacuum Metallization and Electroless.
In flame spraying, the metallic powder is heated and melted by Oxygen and gas. Then it is sprayed as a metallic coating on the substrate. This process has a high deposition rate and creates very thick layers, but the coatings tend to be porous and somewhat rough. Due to the nature of the application process, coatings can be applied to specific areas of components, which is useful when working with complex or unusually shaped components.
The arc spraying is also the same flame spraying just with difference in power source. Instead of depending on a combustion flame, arc spraying derives its energy from an electric arc.
In vacuum metallization, a metal (typically aluminum) is evaporated in a vacuum chamber. The vapor then condenses onto the surface of the substrate, leaving a thin layer of metal coating. The entire process takes place within a vacuum chamber to prevent oxidation. Depending on the application the plastic parts, maybe a top coating is formed for promoting some properties such as abrasion resistance. The parts which be metalized in this way are applied from automotive interior parts to certain types of foils.
But the Electroless is common because of easy operation and low cost. For doing Electroless process bellow steps are required.
Cleaning the parts is essential for improving the adhesion of metal layer on the plastic.
Acidic rinsing is done for removing the alkaline materials which residues from cleaner step. Normally this solution is based on sulfuric acid.
Sensitive or Etching
For an excellent adhesion between metal deposition and plastic surface, it is essential to make sensitive the surface. For this reason, etching is done by chromic acid with a percentage of sulfuric acid. In this way a rough surface will be result which is important for trapping the palladium particles.
Neutralizing solution is generally based on chloridric acid and is essential for removing the chromic acid residues especial regarding the complex shaped parts.
Palladium ions are trapped into the pores and make activation the surface and prepare for reaction with metal ions.
There are two kinds of Electroless solution in this step. Copper and Nickel Electroless. Each of them has some advantages and disadvantages. For instance Nickel Electroless is cheaper than Copper while Copper deposition result of copper Electroless is more resistant in alkaline solution.
After metallization the plastic surface, bright copper with 12 – 25 micron will be deposited then bright nickel with thickness to 33 micron will deposit. The final deposition is bright chromium about 0.12 – 0.25 micron; of course the final step could be gold, silver, bronze and brass.