Hydrodynamic Shear Driven Inner Layer Copper Trace Washout in Ultra Thin Micro Channels
Controlling wet-process nozzle velocity below two meters per second prevents hydrodynamic trace stripping on ultra-thin inner layer copper channels.
Chemical Etching
Material Removal
Subtractive manufacturing processes use reactive solutions to dissolve unwanted metal from a substrate surface. In printed circuit board production, chemical etching defines the conductive patterns by stripping away copper not protected by a resist layer. The reaction relies on a controlled redox environment to ensure clean trace edges.
High precision requirements limit the technique to specific metal thicknesses and resist types.
Solution Chemistry
Alkaline or acidic reagents provide the necessary ion exchange to convert solid metal into soluble salts. The chemical etching rate depends on the concentration of the etchant, the temperature of the bath, the chemical balance and the agitation of the fluid across the panel. Cupric chloride or ammoniacal solutions are common choices for volume production due to their ability to be regenerated continuously.
As the metal content in the solution increases, the reaction speed fluctuates, requiring automated dosing systems to maintain a steady rate. Consistent chemistry prevents the over etching of fine features.
Edge Profile
The lateral dissolution of metal beneath the protective mask creates a characteristic slope known as undercut. Because chemical etching is isotropic, the solution removes metal horizontally at the same time it moves vertically. This effect reduces the finished width of the conductor compared to the original design.
Design for manufacturing rules include an etch factor to compensate for this expected narrowing. Tight control of the spray pressure and conveyor speed minimizes the deviation from the intended trace geometry.