Optimizing Modified Semi-Additive Process Parameters for Sub-30 Micron Feature Generation
Sub-30 micron mSAP feature generation requires controlling seed layer thickness, LDI resist profiles, plating additive dynamics, and flash etch undercut.
Organic Additive Suppressors
Chemical Function
Acidic electrolytic plating baths utilize organic additive suppressors to manage the local deposition rate on copper surfaces. These molecules adsorb onto high energy sites to impede metal ion reduction by creating a protective molecular film. Uniform thickness across complex printed circuit board geometries relies upon the migration of this additive to recessed areas where electrical current density is lowest.
Controlled diffusion kinetics determine the throwing power of the plating process.
Bath Composition
Precise concentrations of these compounds ensure the copper builds at a constant speed in through-holes and blind vias. High levels of the agent inhibit growth too aggressively, resulting in brittle deposits or complete plating voids. Inadequate amounts allow excessive deposition at board edges where lightning rods or protruding features attract high current.
Analytical titration monitors the active level of these surfactants to maintain the chemical health of the plating electrolyte. Operators replace or replenish the solution based on these measurements to prevent dendritic growth or uneven grain structures.
Performance Impact
Mechanical reliability of the finished via depends on the consistent distribution afforded by these agents. Proper suppression minimizes internal stresses that lead to barrel cracking during thermal cycling or soldering operations. Defective boards often exhibit non-conforming copper thickness that fails microscopic cross section inspection after fabrication.
Effective chemistry minimizes reject rates by standardizing the metal crystal orientation across the entire panel area.