Effect of organic additives on copper electrodeposition in the manufacture of printed boards

This publication deals with the development of a domestic technology of electrochemical copper plating of holes in printed circuit boards (PCBs) that complies with the state-of-the-art requirements for the throwing power, lifespan, and stability of electrolyte.To detail the mechanism of the action of functional additives and select the most suitable ones, we have studied the effect of organic additives on polarization of copper reduction and the leveling ability of an electrolyte with the base composition (g/L): 100 CuSO4•5H2O; 200 H2SO4 (96%); 0.11 NaCl.Polyethylene glycol PEG 4000 (1 g/L) was studied as an inhibitor, Janus Green B (JGB, 6 mg/L) and polyethyleimine (PEI, 6 mg/L) as leveling agents; and sodium 3-mercapto-1-propanesulfonate (MPS, 5 mg/L) as an accelerating (brightening) agent.It was found that the addition of chloride ions (67 mg-ion/L) to the base solution results in depolarization of copper reduction (~50 mV at ic = 2 А/dm 2 ).The additive-free base electrolyte shows negative leveling: the ratio of the coating thickness in a microindent (MCI) to that on a microprotrusion (MCP) is V/=0.70.It was found that addition of an inhibitor (PEG 4000) or leveling agent (JGB or PEI) to the base electrolyte results in the inhibition of copper reduction (by 200, 25 and 120 mV, respectively), while the addition of an accelerating agent (MPS) virtually does not affect polarization.The addition of MPS to the base solution that already contains an inhibitor and a leveling agent also weakly affects polarization, while the addition of MPS to the base solution that contains only the inhibitor results in depolarization of copper reduction.If the solution of PEG 4000 contains JGB or PEI, the microprofile is leveled insignificantly, which is presumably due to refining of the coating crystal grains.The addition of MPS (5 mg/L) to the base solution results in leveling of the microrelief as a result of coating electrodeposition.It has been found that a combination of PEG 4000 (1 g/L), JGB or PEI (6 mg/L), and MPS (5 mg/L) in a solution makes it possible to deposit uniform-thickness coatings both in the interior of PCB holes and at the entrance.If MPS (5 mg/L) is added to the electrolyte, the coating brightness increases from 50 to 550-590 GU.The experimental results obtained confirm the hypothesized mechanisms of the action of the inhibiting, leveling, and brightening additives to the electrolyte employed for the copper plating of PCB holes.