Metallization Method
An electrochemical deposition process that utilizes external electrical current builds the thick conductive layers on printed circuit board traces and via walls. This method, known as electrolytic copper plating, occurs after a thin, primary layer of electroless copper has been chemically deposited to make the non-conductive substrate surface active. The board acts as the cathode in an acid copper bath, drawing copper ions out of the solution to build the required trace thickness.
This plating process is fundamental to creating durable electrical interconnections across multiple board layers.
Bath Chemistry
The plating solution contains copper sulfate, sulfuric acid, and trace organic additives that regulate the deposition rate across different regions of the board. Organic brighteners, carriers, and levelers are added to the bath to ensure the copper is deposited smoothly and that it fills microvias without leaving internal voids. Sulfuric acid maintains high solution conductivity, which reduces the electrical power required for the process.
If the concentration of these additives drifts outside narrow limits, the plated copper can become brittle, leading to cracks during subsequent thermal testing.
Thickness Control
Controlling the current density and the plating time determines the final thickness of the copper layer on the traces. Standard production runs typically target a surface plating thickness of twenty-five microns to meet IPC Class 2 requirements. Regular cross-sectioning and micro-measurement verify that the plated copper is distributed evenly across both outer layers and via barrels.
