Microvia

Abstract: Influences of forced convection during acid copper electroplating on microvia fill of printed circuit boards were studied. The plating formula was composed of polyethylene glycol (PEG), chloride ion, 3-mercapto-l-propanesulfonate, and Janus green B (JGB). The filling performances under various plating conditions were examined with scanning electron microscopy and optical microscopy. Chemical and physical interactions between these additives and fluid dynamics were characterized by cyclic linear sweep voltammetry, steady-state current-potential measurements, linear sweep voltammetry, and galvanostatic measurements using different rotation speeds of working electrode. Experimental results indicated that the potential-dependent adsorption of chloride ion on the copper surface determined and governed the electrochemical effect of these organic additives on the cathode, resulting in a convection-dependent adsorption of inhibiting reagents and an asymmetrical fill of copper deposit in the microvias. A synergistic inhibition effect on the copper deposition caused by a composite suppressor composed of PEG, Cu + , Cl - , and JGB was demonstrated. The dominance of the competitive adsorption between the accelerator and the composite suppressor was shown to depend significantly on the chloride ion concentration and on the forced convection.

Abstract: Microvia filling by copper electroplating was carried out using a plating bath containing a suppressor and a leveler without an accelerator. The required accelerator was adsorbed onto the copper seed layer of the microvia in a predipping bath before the filling plating. This pretreatment is similar to the self-assembled monolayer of thiol molecules that forms on a copper surface. The suppressor was poly(ethylene glycol) (PEG), and five levelers, namely, Janus green B, diazine black, methylene violet, safranine O, and Alcian blue, were employed to screen for the best plating formula suitable for a plating process in which no accelerator was present in the plating solution. The thiol molecule employed in this work was 3-mercapto-1-propanesulfonate (MPS). The electrochemical behaviors of various plating formulas were characterized using a galvanostatic measurement on a copper electrode at different rotating speeds. Results indicated that the MPS adlayer is transferable onto the surface of the copper deposit and can be displaced by the PEG-C1-leveler. The displacement rate depends on the molecular structure of the added leveler. This plating process has the potential to greatly reduce the plating time of microvia filling.