Research On Plating Additives For Filling The Microvias In Printed Circuit Board

As the mother board of electronic products,Printed Circuit Board(PCB)is the substrate that connects and carries electronic components.With the rapid development of5G communication technology,high-end electronic products put forward higher requirements for PCB miniaturization and multi-levelization,microvias connecting PCB layers are gradually becoming smaller and higher density,and the application of high-density interconnect(HDI)printed circuit board in electronic products is growing rapidly.However,efficient additive formulas used in microvia filling are basically monopolized in foreign suppliers.Therefore,it has become an urgent task for the domestic PCB industry to develop and research efficient additive formula with independent intellectual property rights.In this paper,the aim was to develop an efficient additive formula for microvias electroplating.Firstly,the screening conditions of leveler was put forward,and the effect of leveler was evaluated by theory and practice.Secondly,the interaction mechanism of additives was studied.Finally,the relationship between microvia filling rate and cathode potential difference under strong and weak convection was studied,a method for rapid screening of additive concentration range was established,and the additive formula was optimized and verified by experiment.The specific research contents and conclusions are as follows:(1)Based on the mechaism of convection-dependent adsorption(CDA),It was proposed that the cathode can generate a forward potential difference,which reprensented the potential difference of the working electrode at 100r/min and 1000r/min in the galvanostatic test(??=?_100r/min-?_1000r/min),and the organics with strong adsorption capacity were selected as potential leveler.(2)Based on the screen conditions of leveler proposed in this article,APTDC and BMB were selected as potential microvias filling leveler.It was verified by XPS experiment,quantum chemistry calculation,and molecular dynamics simulation.(3)BMB and APTDC were used as potential leveler,and combined with Cl^-,PEG10000 and SPS as additive system for microvia electroplating.The result showed that both APTDC and BMB were effective levelers.And APTDC had better microvia filling rate,leveling effect,and the copper thickness on the plating surface was thinner.The performance of the corresponding HDI products was better.(4)The interaction among Cl^-,PEG10000,SPS and APTDC additives was studied.Electrochemical experiments showed that:The effect of APTDC and SPS only occurs when PEG and Cl^-coexist.When the four additives coexist,the difference of cathodic potential and current was shown,which indicated that PEG-Cl^-could not only cooperate with APTDC to inhibit copper deposition in strong convection,but also assist SPS to accelerate copper deposition in the weak convection.Through the synergistic effect of the four additives,microvia could be filled perfectly.Electroplating experiments showed that APTDC could increase the passable current density and effectively inhibit the overfilling of microvia electroplating(5)Single factor experiment showed that when the concentration of Cl^-was 20-120mg/L,the concentration of PEG was 0-400 mg/L,the concentration of SPS was 0-7 mg/L,and the concentration of APTDC was 0-7 mg/L,??and the filling rate were present good consistency.When??more than 20 mv,the filling rate of microvia with a depth-to-diameter ratio of 60/100?m and 90/100?m was higher than 85%,and the higher the??value,the better the filling effect.Therefore,a rapid screening method using??vaule obtained by galvanostatic test as the concentration range of additives was proposed.(6)The formula of microvia electroplating additive optimized by orthogonal experiment was:Cl^-60 mg/L?PEG 200 mg/L?SPS 2.5 mg/L?APTDC 2 mg/L.Under these conditions,the average filling rate of microvia was 93%,and the average surface copper thickness was 14.7?m.Compared with the production line bath,the microvia filling rate of optimized formula was slightly higher,and the thickness of the surface copper could be reduced effectively.