Effects of supporting electrolytes on copper electroplating for filling through-hole

摘要

The filling of micron through-holes (THs) in a printed circuit board (PCB) by copper electroplating was investigated in this study. The role of supporting electrolytes, such as H_2SO_4, Na_2SO_4 and K_2SO_4, was explored using practical TH filling plating and linear-sweep voltammetry (LSV) analysis of plating solutions. The copper could selectively fill THs using one organic additive, namely, tetranitroblue tetrazolium chloride (TNBT), as an inhibitor. The inhibiting strength of TNBT depended on the supporting electrolytes. Although H_2SO_4 could enhance the inhibiting strength of TNBT, it also decreased the filling capability of the copper plating solution; Na_2SO_4 and K_2SO_4 did not enhance the inhibiting strength of TNBT but they increased the filling capability of the copper plating solution. Additionally, the protons could chemically interact with TNBT to form precipitate, whereas sodium and potassium ions did not easily interact with TNBT. The filling capability of the copper plating solution using Na_2SO_4 and K_2SO_4 as supporting electrolytes could be greatly improved by adding a small amount of bis(3-sulfopropyl)-disulfide (SPS) and poly(ethylene glycol) (PEG) with a molecular weight of 600.