Novel, Simple, and Green Citrate-Based Copper Electronic Electroplating Bath in Microvia Void-Free Filling for Printed Circuit Board Application

In this work, a novel, simple, and green citrate-based copper electronic electroplating bath with the characteristics of weak corrosion, low copper ion concentration, and simple composition is developed in microvia void-free filling for printed circuit board application. Succinimide (SM), regarded as a leveler, is the core component of the bath. The action mechanisms of SM on microvia void-free copper filling are carefully expounded. UV–vis spectroscopy and theoretical calculations demonstrate that only the Cu2(Cit)22– coordination ion exists in the bath containing SM at pH 9.0. Linear sweep voltammetry and in situ Fourier transform infrared spectroscopy combined with X-ray photoelectron spectroscopy experiments illustrate that SM can inhibit the electroreduction of the Cu2(Cit)22– coordination ion and promote the electroreduction of intermediate Cu(I) to Cu(0), resulting in the improvement of coating quality. Galvanostatic measurements reveal that the reduction of the Cu2(Cit)22– coordination ion is electrochemically controlled, and SM is diffusion-controlled. The leveler properties of SM (diffusion control and inhibition of Cu2(Cit)22– coordination ion electroreduction) promote copper in bottom-up growing and void-free filling of microvias.