What is Electroless Copper
Electroless copper is a process to chemically deposit a thin layer of copper onto the walls of holes in the PCB. This process creates a conductive layer on the non-conductive glass cloth and resin walls of the holes, enabling the subsequent electroplating of a thicker layer of copper.
The electroless copper plating process involves an autocatalytic oxidation-reduction reaction. It begins with the preparation of the PCB panels, which are clamped into jigs and undergo a series of chemical and rinsing baths. The first step is alkaline degreasing, which ensures the removal of oil, dust, fingerprints, and other debris from the board surface, including the holes in the PCB panel board.
After degreasing, the charge adjustment step follows, where the resin surface is transformed from a weak negative charge to a weak positive charge. This adjustment, also known as “Super Impregnation,” facilitates the effective absorption of activators on the hole walls in later processes.
Next, the cleaning/washing step is crucial to eliminate any contamination resulting from the previous processes. This thorough cleaning ensures a proper and tight bonding between the chemically deposited copper on the walls and the substrate plated copper.
The final step in the electroless copper process is micro-etching, which roughens the surface to create a strong adhesion between the chemically deposited copper and the copper substrate. This step removes oxide from the surface and creates a coarse active copper surface that can effectively absorb colloidal palladium.