Research On Levelers For Filling Electroplated Copper Microvias In Printed Circuit Board Industry

The manufacture of electronic products is inseparable from the important component of Printed Circuit Board?PCB?.The filling electroplated copper microvias process in the printed circuit board manufacturing process is a key technology for realizing interlayer interconnection.With the development of printed circuit boards towards lightweight,high-density interconnect technology,the reduction of the diameter of the microvia and the increase of the aspect ratio of the microvia make it more and more difficult to achieve microvia"overfilling".At present,the additives commonly used in China are provided by American Atotech Co.,Ltd.Although this additive is very effective in achieving microvia"overfilling",the additives and supporting facilities make the cost greatly increased,and for some traditional levelers such as Janus green B?JGB?,Diazine black?DB?,etc.,have their own scope of application.When the diameter of the microvia is reduced,"void"phenomenon often occurs.Therefore,it is very important to find a universal leveler.In this paper,2-amino-4-methylbenzothiazole?AMBT?and tricyclazole?TCA?were selected as novel levelers for filling electroplated copper microvias and the effects on filling electroplated copper microvias were studied.In order to obtain a high quality microvia with the diameter of approximately 105?m and the depth of approximately 85?m,the microvia roundness and the ratio of lower and upper aperture were used as experimental indexes,and the effect of the CO₂ laser drilling parameters?laser energy,pulse width,number,mask dimension?on microvias were studied by orthogonal experiment.The optimal parameter combination is determined,namely:laser energy:11 mj,copper pulse width:14?s,resin pulse width:5?s,copper pulse number:1,resin pulse number:3,mask dimension:2.0 mm.The corrosion inhibition effects of AMBT and TCA on Q235 steel and copper in 0.5M sulfuric acid solution were studied by electrochemical test,Scanning Electron Microscope?SEM?test and theoretical calculation.It reveals that both AMBT and TCA can adsorb on the copper surface,inhibiting the copper surface from being attacked by the external corrosive environment.Moreover,TCA has smaller E_LOMO,?E values and a larger?value,indicating that TCA has more adsorption sites than AMBT,and is more easily adsorbed on the copper surface.The provid data supports for their selection as levelers and pave the way for the study of filling electroplated copper microvias.The microvia filling rate was tested as a test index,and the single-factor test was performed to filling microvia for 75 min at a current density of 1.6 A/dm².It is obtained that the presence of 220 g/L CuSO₄?5H₂O,53 g/L H₂SO₄,60 mg/L Cl^-,1 mg/L sodium polydithiodipropane sulfonate?SPS?,200 mg/L polyethylene glycol?PEG-8000?and 2mg/L TCA can achieve the better microvia filling effect.The filling rate of TCA for microvias with the diameter and depth of about 90?m is up to 87.98%,and the microvia filling rate for the diameter of about 105?m and the depth of about 85?m is 91.20%under the preferred combination of parameters,which indicates that small changes in the aspect ratio of the microvia also affect the filling rate of the microvias.The above studies have shown that TCA can not only be used as a new type of inhibitor in the field of metal anti-corrosion,but also has a good effect on filling electroplated copper microvias,reflecting the dual practical application of TCA.The electrochemical impedance and cathodic polarization curves of different plating solution formulations reveal that various additives are interactive,and TCA can enhance the inhibition of copper deposition,which is enhanced with the increase of TCA concentrations.SEM test indicates that the electroplated copper surface is smooth at low concentrations of TCA,but when the TCA concentration is greater than 3 mg/L,many fine crystals appear on the copper surface.Moreover,the Cu?220?surface gradually becomes the main orientation of the copper plating by X-ray diffraction?XRD?test.Atomic force microscopy?AFM?and theoretical calculations show that TCA can rely on the donor-acceptor interactions between the benzene ring with?-electrons,heteroatoms?S,N?or–C=N–and the vacant orbitals of copper atoms directly adsorbing on the copper surface.X-ray photoelectron spectroscopy?XPS?further reveals that Cu-N-C or Cu-N=C structures may be formed on the surface of the TCA-modified copper.The electrostatic potential?ESP?diagram of TCA shows that the main adsorption site of TCA on the copper surface is the N atoms on the triazole.Molecular dynamics simulation results of different crystal faces show that TCA is not preferentially adsorbed on the Cu?111?surface with the highest interaction energy,but adsorbed on Cu?220?due to the influence of various additives and plating conditions in the plating solution.The adsorption of TCA on the Cu?220?surface inhibits the deposition of copper on the Cu?220?surface,so that the Cu?220?surface becomes the main crystal plane orientation of the copper plating after electroplating.