Flexible PCB Annular Ring Step Height Reduction

The patent applies preliminary action by performing copper reduction on the inner wall of the hole before forming the annular ring. The reducing agent is introduced to reduce copper ions on the inner wall, creating a reduced copper layer that serves as a foundation for subsequent plating. This preliminary reduction step ensures that when copper is later plated to form the annular ring, the step height is controlled because the plating builds upon the reduced copper layer rather than creating a large step from the original substrate level.

The patent applies local quality by introducing a reducing agent into the hole to create a localized reduced copper layer on the inner wall. This localized reduction creates different copper densities and heights at different locations: the bottom and inner wall of the hole have reduced copper layers, while the surrounding area maintains the original copper layer thickness. This local differentiation allows the formation of annular rings with controlled step heights that enable fine line production even in multilayer circuits.

The patent applies parameter changes by modifying the copper layer parameters through chemical reduction. The reducing agent changes the copper ion concentration and distribution on the inner wall, creating a reduced copper layer with different physical and chemical properties. This parameter change in copper density and layer thickness enables the subsequent plating process to form annular rings with smoother surfaces and reduced step heights, improving both reliability and surface quality.