Electrodeposited Copper Additive Dynamics in Printed Circuit Board Fabrication
Controlled additive balance between suppressors, accelerators, and levelers drives bottom-up microvia filling, requiring strict CVS control to avoid scrap.
Janu Green B
Meaning
Synthetic phenazine-based basic dyes serve as functional grain-refining additives and leveler components in acid copper electroplating chemistries. The heterocyclic compound known as janu green b functions by selectively adsorbing onto high-potential planar surfaces and via shoulders during circuit board metallization. By creating a localized polarization barrier, it inhibits excess copper deposition on flat dielectric regions while permitting accelerated growth at recessed microvia bottoms.
The technical application stops at electrodeposition baths, finding no operational utility in dry etching, solder reflow or laminate pressing operations.
Electrochemical Function
Selective suppression of electrodeposition occurs because convective fluid flow delivers the leveler molecule more rapidly to projecting corners than into stagnant microvia cavities. In typical acid copper electrolytes containing sulfuric acid and copper sulfate, janu green b cooperates with chloride ions to increase cathodic overpotential at protruding board features. The resultant potential gradient directs cupric ions toward blind microvias where leveler concentration remains minimal.
This controlled mass-transfer differential prevents early mouth closure and subsequent internal void formation during high-density interconnect fabrication.
Bath Degradation
Cathodic consumption and chemical breakdown under strong acidic conditions alter the molecular structure of the dye over continuous production cycles. Electrolytic reduction cleaves the azo linkage within janu green b, converting the active leveling agent into inactive aromatic fragments that accumulate as bath contamination. High concentrations of these breakdown products reduce plating ductility, introduce tensile stress into the copper layer, and trigger microvoiding during thermal shock tests.
Plating line operators must periodically remove these organic contaminants using activated carbon treatment procedures to preserve deposit elongation standards.
Process Surveillance
Electrochemical verification through cyclic voltammetric stripping provides precise quantification of active leveler concentration inside running baths. The operating concentration of janu green b is maintained within a narrow window of one to ten milligrams per liter to avoid surface embrittlement. Exceeding this boundary produces severe over-inhibition, retarding overall plating rate and inducing nodular surface defects across copper traces.
Process management requires strict synchronization between chemical dosing pumps and cumulative ampere-hour meters on the automated plating line.