The history of electroless copper plating can be traced back to 1947, but it was not commercially recognized until the mid-1950s. It was not until 1959 that electroless copper plating was widely used for hole metallization in double-sided printed circuit boards, rather than mechanical hollow rivets. However, the service life of the early electroless copper plating solution was only a few hours, and the stability of the plating solution was poor, which was not suitable for continuous production. By the 1960s and 1970s, electroless copper plating technology had made great progress. Some well-known printed circuit manufacturers and material suppliers in the world have successfully developed a series of electroless copper plating solutions, which are widely used in the printed circuit industry.
The electroless copper plating process was successfully applied to the hole metallization of double-sided printed circuit boards in my country and in the 1960s. The engineers and technicians of the North China Institute of Computing Technology and the Institute of Computer Science of the Chinese Academy of Sciences succeeded in absorbing foreign patented technology. A new type of electroless copper plating solution with different characteristics has been developed and successfully applied in many domestic units.
The electroless copper plating process is as follows:

Drilling → deburring on the grinding plate → upper plate → cleaning and finishing treatment → double water washing → micro-etching chemical roughening → double water washing → prepreg treatment → colloidal palladium activation treatment → double water washing → accelerated treatment → double water washing → copper sinking → upper plate →Upper plate→Acid pickling→Sub-copper→Water washing→Lower plate→drying

The operation is simple and convenient, the process is easy to control, the etching speed is constant, the roughening effect is uniform, and the cost is reduced. The colloidal palladium activation solution can eliminate the loose catalytic layer formed on the copper foil. The colloidal palladium activation solution has good activity and significantly improves the quality of the electroless copper plating layer. The electroless copper plating process for multilayer boards is basically the same as that for double-layer boards. The difference is that after deburring the multilayer board, it should be treated with stains or pitting.
Introduction to part of the process.