Investigation Of Smooth Copper Deposition With Additive Regulation For Printed Circuit

With the 5G communication network developing globally,digital signal transmission speed keeps increasing rapidly,and the micron level roughness of transmission lines no longer satisfies the requirement of signal transmission loss,which lead to great challenges for PCB.In this study,to adjust the roughness of the copper electroplating via add additives,the chemical and physical as well as electrochemical properties of three common used additives in acidic copper electroplating were studied to further reduce the coating’s surface roughness.According to the results,high performance additives were selected for PCB manufacture process,and after studying the properties systematically,the result indicated that the selected additives decreased the insertion loss up to 19.7%,which increased the signal integrity of the transmission lines effectively.Firstly,of molecular dynamics simulation,quantum chemistry calculation and electrochemical analysis of the three common used additives(SPS,JGB and EO/PO)were investigated.The results of molecular dynamics simulation demonstrated that EO/PO possesses the highest stability during adsorption on copper surface thus leading to a great inhibitory effect on copper deposition.However,the depolarization effect of SPS was decreased,which is because JGB would disturb the adsorption on copper surface of partial SPS.EO/PO owns the most stable properties and the lowest reactivity in the electrodeposition,which is confirmed by quantum chemical calculation results.On the contrary,JGB has highest chemical activity,therefore,it’s more likely to transfer electron and produce reaction.Electrochemical results illustrate the acceleration effect of SPS and strong inhibition effect of EO/PO can reach an equilibrium state.In addition,JGB shows strongest inhibition effect when electrolytes containing SPS-EO/PO.Next,electroplating experiments with different additives formulas containing SPS,EO/PO and JGB were designed and carried out to screening the optimal formula enables the best leveling performance.Various surface morphologies and crystalline orientation of plated copper films were characterized by a scanning electron microscope(SEM)and X-ray diffraction(XRD),respectively.The optimal formula contains SPS,EO/PO and JGB.In this formula,electrochemical nucleation and growth was depressed because of the presence of EO/PO,on the other hand,copper nuclei in the non-preferred area of copper deposition was produced in the presence of SPS which ensures the uniformity of deposition.The competitive adsorption of SPS and EO/PO leads to a stable and uniform fine crystallization.Orthogonal experiments were designed based on the copper’s surface roughness.The results show that the concentration of SPS has greatest effect on the surface roughness.The surface roughness decreases with the increasing of SPS’s concentration.The EO/PO concentration has little relation with the coating’s surface roughness.In addition,the increasing of JGB concentration leads to a rougher copper surface.Finally,based on the optimized additives formula,a series of verification tests aim to improve the signal integrity of transmission lines are designed.A test board which can be used for insertion loss test in laboratory environment is designed and the results show that the additives formula including SPS-EO/PO-JGB can significantly reduce signal transmission loss of transmission lines in the fabrication process,and signal integrity is improved.