Study Of Electroplating Copper Additives For Filling Holes On Printed Circuit Board

With the rapid development of electronic terminal products towards miniaturization in recent years,high-density interconnected(HDI)multilayer plates emerge as the times require.Through-holes,blind vias,and buried vias in the layers between the layers in the multilayer board are increasingly used in printed circuit board(PCB)manufacturing processes.The excellent conductivity of copper makes it the main body of conductive circuit in PCB.With the increases of the thickness of the laminate,the aperture decreases gradually and the ratio of thickness to diameter increases.And the distribution of the electric field in the hole is not uniform,which results in the formation of holes in the process of hole filling electroplating and the decrease of electrical performance.One of the ways to solve this problem is to adding different additives to the electroplated copper plating solution which obtain a bright copper layer and meet process requirement of copper layer with thickness.In this paper,the optimum technological parameters are obtained by orthogonal experiment,and the adsorption mechanism of additives on copper surface is studied by electrochemical method.The adsorption behavior and kinetic process of accelerator on copper surface are studied by molecular dynamics simulation and quantum chemical calculation.1.The formula of hole-filling plating copper was studied and the technological conditions are optimized.(1)The effect of the concentration of copper additive on the performance of plating is discussed.The results showed that the accelerator and inhibitor had the greatest influence on the brightness and adhesion of the plating.The best formula is aliphatic amine ethoxyl sulfonates(AESS)25.0 mg/L,Polyvinylidene alkyl salt(PN)25.0 mg/L,sodium polydithiodipropane sulfonate(SPS)2.0 mg/L,current density 3A/m2.(2)The effect of plating temperature and plating time on the properties of the coating is investigated.The results show that the thickness of the copper increases with temperature,the optimum plating temperature is 30℃,and the plating time is 2 h.The brightness is basically good.2.The mechanism of the additive is studied by electrochemical test.The electrochemical results showed that the polarization potential shifted negatively with the addition of accelerant,and the coverage of SPS and MPS on the electrode surface were 0.44 and 0.30,respectively.3.Study the frontier orbitals,Fukui index and energy changes of the adsorption process of additive molecules sodium 3-mercapto-1-propane sulfonate(MPS)and SPS on the Cu surface.The molecular dynamics results show that the adsorption energies of SPS and MPS on Cu(111)surface are-280.35 kcal/mol and-239.03 kcal/mol,respectively,indicating that both accelerator molecules could spontaneously adsorb on Cu surface.The energy orbital results indicate that the adsorption of the lone pair of accelerator with the empty orbital of Cu to form a coordination bond,and the active group of the accelerator is a sulfonic acid group,a disulfide bond and a sulfhydryl group.And according to the adsorption energy and adsorption morphology of the accelerator,it is proved that the accelerator can strongly adsorb with the Cu surface.On this basis,a new accelerator,1-sulfhydryl-4,5-thioctane sulfonic acid sodium(SSPS),is designed.The further analysis shows that the adsorption energy of SSPS is-229.85 kcal/mol,property and calculation results were similar with existing additives.It is proved that SSPS can generate strong adsorption and can exert the expected effect of accelerator.