Optimization Study On The Through Hole Electroplating And White Mist Of High Aspect Ratio Printed Circuit

Through-hole copper electroplating is one of the important ways for the printed circuit board to realize electrical conduction between layers.The quality of the copper plating seriously affects the quality and reliability of electronic products.With the trend of miniaturization and high integration of electronic products,printed circuit boards are also developing in the direction of high density and high aspect ratio,and copper plating in high aspect ratio through-hole imposes higher requirements on copper electroplating technology.Electroplating copper results are affected by many factors,such as the plating solution,electroplating equipment,operator,pre-plating treatment,etc.Therefore,it is necessary to improve the copper coating performance from various aspects.This paper focuses on the optimization of through-hole metallization of high aspect ratio PCB.We mainly studies the application of data analysis methods in electroplating copper,copper-plating formula for high aspect ratio,and abnormal handling of copper electroplating.Throwing power is an important quality index of PCB through-hole plating.So the analysis of throwing power data has also become particularly important.At present,most of the methods for analyzing TP data in the industry are averaging the data of multiple measurements.A few more of them use box plots for intuitive analysis.Although this method is simple and easy,the analysis of data is not thorough,Therefore,the ability to solve problems is limited.Variance analysis and multiple comparisons are two common data analysis methods,which are widely used in scientific research and industrial production.This paper elaborates on the theory and calculation methods of variance analysis and multiple comparisons,three common problems in industries were solved by using these two methods: effect of leveler concentration on TP,difference analysis of repeated experiments,and scientific analysis of industry experience.At present,most of the bath formulation using for plating high aspect ratio through-hole are supplied by foreign companies,such as Rohm and Haas,Atotech,Shangcun Chemical,Schlott,etc.We urgently need to research and develop bath formulation for high aspect ratio THs electroplating with independent intellectual property rights.In this paper,Cyclic voltammetric stripping(CVS)and Harlem bath plating experiments were used to screen suppressors,an suppressor codenamed CM74023 was the most remarkable,whose effective concentration range was 400~600ppm;Harlem bath plating experiments were used to screen levelers.an leveler codenamed XR170208 was the most remarkable,whose effective concentration range was 40~50ppm;SPS was adopted as brightener,It was found that the low concentration of copper sulfate can promote mass transfer and TP,Therefore,the concentration of copper sulfate is 50 g/L.Finally,the parameters of the formulation are determined.White mist occurred when electroplating holes depositing with conductive polymers,this abnormal phenomenon was studied in this article.The surface morphology was observed by metallographic microscope and SEM,and many abnormal copper spots can be found on the white board.It can be found through Harlem plating experiments that sodium polystyrene sulfonate(PSS)used in making hole conductive can lead to white mist;CVS test was carried out to get insight to the electrochemical mechanism of the white mists phenomenon.It can be found that the PSS could change the overpotential of the Copper electroplating,so the Nuclear growth became faster;molecular dynamics simulation was performed to study the adsorption of sodium polystyrene sulfonate on the copper surface.At last,two processes including microetch and brushing were proposed to solve the problem.