Electroless is a process which a metal layer is deposited on the dielectric surfaces by a reduction agent and without an electrical power. Metallization of dielectric surface has known since lots time ego. Electroless process innovated in 1946. In 1948, Wien, during his researches regarding to the metallization dielectric surfaces with copper, applied a two stages process for activation dielectric surface , but this product couldn`t get to the manufacturing because of the high price also low stability and rapidly decomposition.
Motorella Company has introduced copper plating for connection two sides of a board between 1953–1955. It was a suitable way for manufacturing.
Nearby 40 years the dominant method for connection the holes contains catalytic processes which be followed by electroless with copper deposition.
Application of direct metallization which has been developed in 80 decant performed an electric layer on the hole`s dielectric surfaces. Generally, these technologies are claimed that they are simpler in application and its control also waste disposal is easy in compare with the classical method. The deposition result of electroless has high corrosion and erosion resistance and high hardness. Also the deposition is much more uniform even on the parts with implicated shape. There are kinds of electroless solution contains Tin, Gold, Copper, Nickel, silver and platinum. Copper and Nickel electroless is general. In PCB industrial the copper electroless is more common than nickel because high conductivity. The copper electroless is used for metallization board. In plastic industrial in spite of usage of nickel electroless for lower performance, copper electroless is preferred because it is shown in 1970 that the copper has high resistance in alkaline media, then for high efficiency, the copper electroless is the first chosen special in automotive industrial. The main application of copper electroless is in PCB industrial for PTH (Plated – Through – Hole).The holes cannot be able for direct plating because the board material is dielectric such as epoxy, glass, paper and other dielectrics which couldn`t provide electrical conductivity.