In the process of making the circuit board, it is usually necessary to pass through the hole to realize the transmission of the circuit and the encapsulation. Hole metallization is one of the most important processes in PCB manufacturing technology, in order to realize the hole metallization, usually adopt chemical copper (PTH), black hole (Black Hole) and the method of conductive polymer film to conductive resin substrate.

Chemical copper
Electroless copper plating is the principle of reduction of copper to copper under the condition of reducing agent. The process can be divided into three steps: pretreatment, activation and deposition of copper.
The basic composition of electroless copper plating solution includes copper salt, complexing agent, reducing agent, pH regulator and additive. One of the most common reducing agent is formaldehyde, two methyl amino borane, hypophosphite, hydrazine hydrate, low metal salt, reducing sugar. Among them, the price of formaldehyde is low and the relative content of copper in the coating is higher, so it is the most widely used and the most widely used. However, formaldehyde is volatile, unstable and other shortcomings, in recent years, how to replace formaldehyde is also the focus of the study. Complexing agent is one of the key components of electroless copper plating, which can increase the polarization of copper ions to reach the crystal fine and bright coating. Common tartaric acid, EDTA, triethanolamine, three isopropyl amine, etc..

Black hole
The black hole is fine drops of graphite or carbon black powder dispersed in deionized water, using surfactants or graphite conductive carbon black suspension remained stable, and has good wetting properties, the graphite or carbon black can be fully absorbed in the non conductor hole wall surface, forming a combination of uniform and meticulous the conductive layer, solid.

Conducting polymer film
Non conductor surface chemical reaction in Potassium Permanganate alkaline water solution, generating a manganese dioxide layer, then in acidic solution, heterocyclic compounds or pyrrole pyrrole monomer Series in non conductor surface and the loss of a proton conducting polymer polymerization, insoluble generation is closely attached to the. Then the circuit board with the conductive polymer is directly plated to complete the metallization.
The process is mainly divided into three parts: pretreatment; formation of conductive polymer; copper sulfate plating.