Microvia Superfilling Process Control

Electrochemical thermodynamics is the foundation of the microvia fill process, whose model represents the mass conservation of species (copper ions and surfactants) in the condition of moving boundary. The shape of via changes due to the deposed metallic copper, whose growth depends on the blocking effect of surfactants, which in turn depends on the boundary curvature. The via filling process is controlled through the boundary by adjusting the electric current flowing through the bath system. Maximizing the current raises the via fill process speed but ends up in depletion of the copper ions at the bottom of via causing an incomplete via fill (poorly fabricated board). In this paper the problem is solved by adjusting the concentration of copper ions to a reference value near the panel surface of the plated board. The stabilizing control is proposed based on the developed via fill model. By applying the control, the via fill process can be sped up by ca. 20% and the via dimple minimized 5% without risking product output quality.