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)2]2– 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)2]2– 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)2]2– coordination ion is electrochemically controlled, and SM is diffusion-controlled. The leveler properties of SM (diffusion control and inhibition of [Cu2(Cit)2]2– coordination ion electroreduction) promote copper in bottom-up growing and void-free filling of microvias.