Study On The Mechanism And Application Of Acid Electroplated Copper Plating Additives For PCB

A printed circuit board(PCB)is an important part of an electronic product and is a carrier for supporting electronic components in electronic products.It is widely used in various electronic devices.With the continuous progress of society,the electronic products pursued by mankind are rapidly becoming smaller,more convenient,and more intelligent.The development of high-density interconnect multilayer printed circuit boards(HDI-PCB)is an important part of manufacturing these complex electronic products.At present,in order to meet the social requirements,the diameter of the microvia of the PCB is continuously shrinking,and the depth-to-diameter ratio of the microvia is getting larger and larger,and the requirements for the PCB plating process are higher.Microvia metallization is the core of PCB electroplating Cu,and it is one of the main ways to achieve the connection between layers of multi-layer circuit boards.It is also one of the very important technologies in current PCB manufacturing processes.However,in the DC electroplating process,due to uneven distribution of current density in the microvia,the current density of the orifice is relatively large,and the phenomenon of plugging is likely to occur,resulting in a decrease in the filling quality of the microvia.Therefore,in order to obtain a good microvia filling performance and uniform copper plating,the method of adding organic additives in the plating solution is very effective and economical.For this reason,the main goal of this study is to fill copper plating additives with microvia.Firstly,various components of microvia plating additives are pre-screened and verified by electroplating tests to determine the combination of additive systems.Secondly,the effects of various additive components on the copper filling ofmicrovia in PCBs and their performance characterizations were studied.The main contents and conclusions were given as follows:1?Microviaplating additive screening and system determination(1)Through a comparative analysis of previous studies by a large number of scholars,suitable halogen ions(chloride ions),accelerators(SPS)and inhibitors(PEG-8000)were determined.(2)With the help of a method for screening metal corrosion inhibitors,two suitable electroplating levelers(DMP,TBA)are selected.The adsorption behaviors and adsorption mechanisms of DMP and TBA molecules on copper surfaces were explored by atomic force microscopy(AFM)and X-ray photoelectron spectroscopy(XPS)combined with quantum chemical calculations and molecular dynamics simulations.It is proved that when the DMP and TBA molecules are adsorbed on the copper surface in parallel through the pyrimidine ring,the effective area for electrochemical reaction is reduced,the slower the deposition rate of the copper surface,and the more uniform the deposited layer,which is beneficial to the fill of microvia,and also indirectly proved that they may be a potential,effective plating leveler.(3)The DMP and TBA molecules were combined with Cl~-,SPS,and PEG-8000,respectively,and verified by electroplating experiments.It further proves that both DMP and TBA molecules are effective electroplating leveling agents,which can make microvia filled with super filling patterns.2?Effects of different additives on microvia copper-filling efficiency of PCB(1)The effect of different mass concentrations of Cl~-,SPS,PEG-8000 and DMP with better filling performance on microvia-filling efficiency wasstudied.The results showed that the microvia-filling efficiency is the best when the mass concentrations of Cl~-,accelerator,inhibitor and leveler are 30-60 mg/L,0.5-1.0 mg/L,100-300 mg/L and 1-7mg/L respectively.(2)In the presence of other additives,chloride ions can interact with PEG-8000 and DMP at low concentrations to inhibit the deposition of copper,and chloride ions react with copper(I)to produce CuCl to accelerate the deposition of copper at high concentrations.(3)From the FE-SEM images and XRD measurements results indicated that a uniform,compact and smooth surface can be obtained when lower concentration of DMP added to electroplating solution.However,when higher DMP concentration added to the electroplating solution,copper surface appeared acicular crystal,and the(111)orientations of electroplating copper became dominate.(4)Studying the interaction between additives,we can see that when chloride ions are added to the basic bath solution alone,it can accelerate the deposition of copper ions on the cathode surface by changing the reaction history of copper ion deposition;then DMP or PEG-8000 is added to the plating solution,which hinders the reduction of copper ions on the cathode surface,inhibits the deposition of copper ions;When the SPS is added to the plating solution,it can promote the reduction of copper ions on the cathode surface and accelerate the deposition of copper ions.However,only when the four additives are added to the basic plating solution at the same time,the microvia can be filled with super filling patterns.(5)The concentrations of additives were optimized by orthogonal test using fill rate of microvia as the index.The optimal composition of additives was obtained as follows:Cl~-30mg/L,SPS 1.5 mg/L,PEG-8000 200mg/L,2-MP 1mg/L.The coating obtained by this optimize electroplating formula is uniformandcompact and the average filling rate up to 91.2%,and has good resistance to thermal shock in tin immersion and temperature cycling tests,meeting the requirement of reliability for PCB application.