Design Development And Applied Research Of Silver Activation Solution For Electroless Copper Plating Of Printed Circuit Board (PCB)

Electroless copper plating technology is widely used in electronics,materials,machinery,aviation and many other industrial fields,in the printed circuit board（Printed-Circuit-Board,PCB）industry is mainly used for through-hole metallization.Activation technology is a necessary link for electroless copper plating on non-metallic surfaces,and is the core technology.It is a uniform adsorption of a layer of catalytically active metal particles on a non-metallic surface,and they are used to induce subsequent electroless copper plating.Therefore,the uniform activation of the non-metallic surface is a prerequisite for electroless copper plating,and the activation effect directly determines the quality of electroless copper plating,which in turn determines the success of the entire PCB production.At present,the most commonly used activation liquid in the industry is palladium activation liquid,with the requirements of environmental protection and the development of new energy fields,the price of palladium continues to rise,which has led to a sharp increase in the cost of the PCB industry,so it is imperative to develop new activation fluid.In this paper,silver with similar properties to palladium was selected as the active metal,and silver activation solution was developed to replace the use of palladium activation solution.The main research contents and conclusions are as follows:（1）The optimal process conditions of silver ion activation solution and colloidal silver activation solution were studied,and the results showed that the best formula and conditions of silver ion activation solution were:1.8 g/L Ag NO₃,appropriate amount of ammonia,4 m L/L ethylenediamine,p H=11,temperature 45°C,time 25 min.Under the best conditions,the activated liquid obtained is stable,the catalytic activity is high,the coating adhesion is good,the adhesion ASTM grade is≥4B,the mass fraction of surface copper reaches 98.42%,the plating is pink,but the surface of the plating is not smooth enough,the copper plating particles are large,uneven,and grow in clumps.The preparation conditions of colloidal silver activation solution were as follows:the ratio of silver nitrate,stannous sulfate and trisodium citrate dihydrate was 1:50:70-90.The preparation method is:take the weighed trisodium citrate dihydrate dissolved in deionized water,add the weighed stannous sulfate,in order to prevent the hydrolysis of stannous sulfate and affect its reduction,it is necessary to quickly add the silver nitrate solution prepared in advance,under the condition of electromagnetic stirring until all substances are completely dissolved.The optimal activation process is:silver nitrate concentration is 0.002 mol/L,activation time is 10min,activation temperature is 35°C.After the activation process,the obtained copper plating is pink with metallic luster,and the mass fraction of surface copper reaches 98.43%,which meets the requirements of the PCB industry.（2）The activation mechanism of silver ion activation liquid and colloidal silver activation liquid was studied.The results show that the activation mechanism of silver ion activation solution is through the sensitization process to make the plate surface adsorb a layer of highly reducing stannous ions,and then in the activation process with the silver ions and their complexed ions in the activation solution redox reaction to generate silver single particles,attached to the plate surface,in the electroless plating process,these silver atoms as the active center of electroless plating,catalyze the copper plating reaction.The activated adsorption mechanism of colloidal silver activation liquid is physical adsorption,which belongs to electrostatic action to promote adsorption.In the process of electroless copper plating,the silver nanoparticles adsorbed on the plate surface are first oxidized into silver ions,which can play the role of catalyzing the electroless copper plating reaction,and after completing the copper deposition,silver ions are released to continue to catalyze the copper plating reaction.The specific electron transfer mechanism was studied.（3）The reasons for the excellent activation performance of colloidal silver activation liquid were studied.The results show that the reason for the good activity of colloidal silver activation solution is that the（1 1 1）crystal face of silver nanoparticles is prepared,and the main factors affecting the catalytic activity in colloidal silver activation solution are the number and particle size of silver nanoparticles.The number and size of silver nanoparticles are determined by the concentration of silver nitrate.With the increase of silver nitrate concentration,the particle size of silver nanoparticles first increases and then decreases.When the concentration of silver nitrate is 0.0015 mol/L,the particle size also reaches a maximum of 8.719 nm,and the activity of the activation solution is also the best.