Study On Process Of Widening Current Density Range And Electrodeposition Behavior For Electroplating Copper From Pyrophosphate Bath

Due to their advantages of simple bath composition,weak alkaline and non-toxicity,good stability and good dispersion ability,copper pyrophosphate baths are widely used in practical production.However,the operating current density range is narrow,which affects their production efficiency during production.Therefore,it is necessary to add suitable substances,such as additives,to increase the permissible operating current density upper limit of copper pyrophosphate baths.In this paper,traditional screening techniques were used to perform extensive additives.According to the analysis of the Hull cell test results,glycerol has the best effect.In order to better to understand the special role of glycerol in copper pyrophosphate baths,process studies were conducted on alditol additives with similar structure of glycerol.The results show that other alditol additives can not significantly increase the operating current density range of copper pyrophosphate bath,but the addition of alditol additives can improve the structure of coating,which preferring orientation of Cu（111）planes.The single factor study was used to study the effects of different concentrations of glycerol and process parameters on the appearance and micromorphology,crystal structure,and current efficiency for optimized copper pyrophosphate bath.The optimized bath is consisting of potassium pyrophosphate 1mol·L^-1,copper pyrophosphate 0.22 mol·L^-1,glycerol 0.04 mol·L^-1,and the optimized process conditions are under p H=8.9 at 323 K with agitation.The operating current density range increases from 0³.9 A·dm^-2to 0⁵.2 A·dm^-22 after addition.Compared with the conventional copper pyrophosphate bath,the optimized bath can not only widen the used operating current density upper limit,but also results in grain refining,lower porosity,higher flatness,and stable copper content of copper coating.However,the AC/DC superposition technology is effective against conventional copper pyrophosphate bath,but not satisfactory for optimized bath.In order to investigate the role of glycerol in copper pyrophosphate bath,the systematic investigation was studied on the difference in the electrodeposition behavior of alditol additives for copper pyrophosphate bath.The methods,including cyclic voltammetry（CV）,chronoamperometry（CA）,linear sweep voltammetry（LSV）,surface tension test and molecular dynamics simulations,show that all alditol additives mainly adsorb on the electrode surface to change the crystal structure and coating properties during electroplating copper.But in comparison,glycerol has a lower surface tension,and the addition of glycerol increases the hydrogen evolution potential for copper pyrophosphate bath.In summary,it can be seen that the addition of glycerol reduces the surface tension in the optimized bath,the wetting ability of the bath on the cathode surface is better and the hydrogen evolution reaction is more difficult,thereby the operating current density range is increased.According to the tests of CV and CA,the diffusion coefficients of the optimized copper pyrophosphate bath are 2.75×10^-6cm·s^-1and 3.77×10^-6cm·s^-1,respectively,which are consistent with most of the literature reports.