The effect of quaternary ammonium salts with different chain lengths on copper filling behavior in blind holes of printed circuit board

Abstract

The rapid and defect free blind hole copper super filling is the key technology to ensure the quality and development of printed circuit boards (PCBs). The linear quaternary ammonium compounds with a low molecular weight are expected to act as a potential suppressor for blind hole copper filling. Here, three quaternary ammonium salts with different molecular chain lengths (the dodecyl trimethyl ammonium chloride, the cetyl trimethyl ammonium chloride and the stearyl trimethyl ammonium chloride) were selected to study the effects of the molecular chain length of quaternary ammonium salt on the copper filling behavior of the PCB blind holes. The electrochemical results show that the three quaternary ammonium salts show greater inhibition ability on copper deposition compared with the traditional additives (polyethylene glycol (PEG) and Cl−) and furthermore, the suppressor effect becomes stronger with the increase of molecular weight. The blind hole copper filling experiment of PCB is also carried out to study the copper filling capacity of three quaternary ammonium salts. The filling experiment reveals that compared with the traditional suppressors (PEG and Cl−), the filling quality of blind hole copper is significantly improved when the three quaternary ammonium salts are used as suppressors. Moreover, under the coordination of accelerator (bis (3-sulfopropyl) disulfide (SPS)), the three quaternary ammonium salts can realize more rapid copper super filling without chloride ion in the electrolyte. Cross-section and surface morphological analysis further illuminates that the quaternary ammonium salt as an suppressor can also more effectively inhibit the deposition of copper on the PCB surface and reduce the roughness of the copper layer. The present results imply that quaternary ammonium salts have greater advantages for copper filling and are expected to replace traditional suppressors as new suppressors.