Pulse Electroplating Copper And Its Application For High Aspect Ratio Through Hole Interconnection

Copper electroplating is the key technology to realize through hole(TH)interconnection in the process of printed circuit board(PCB)manufacturing.At present,in order to meet the requirements of high-speed and large-capacity transmission of communication and data in 5G era,the design of backplane tends to be large size,multi-layer counts,high thickness and small aperture,which leads to the increasing aspect ratio(AR)of TH.Accordingly,it becomes more and more difficult to achieve uniform coating of copper in TH.In the process of high aspect ratio through holes(HAR TH)electrodeposition,the current density in the center of the hole is much lower than that of the shoulder,which often results in a large difference in the coating thickness between the center and the shoulder of TH.Therefore,it is impossible to achieve good interconnection of HAR TH.In addition,the complex chemical/electrochemical reaction between the anode and the bath additives during the production process will change the concentration of the additives,and produce anode slime and other by-products,which will reduce the throwing power of the plating solution.The goal of this paper is to improve the uniformity of HAR TH coating.The effects of additive components and pulse parameters on the uniformity of coating during electrodeposition,and the reaction between anode and bath additive were investigated.The bath formula of pulse electrodeposition for through-hole interconnection with high thickness to diameter ratio was developed.The specific research contents and conclusions are as follows:(1)The effects of three inhibitors,two accelerators and three levelers on the deposition potential of copper were studied.Combined with the optimization of pulse parameters,the plating conditions suitable for TH with diameter of 200?m and AR of18:1 were obtained.Specifically:virgin make-up solution(VMS:95/40/70)+bis(3-sulfopropyl)disulfide(SPS:3 mg/L)+polypropylene glycol(PEG-8000:1000mg/L)+green dye(10 mg/L);forward current density 2 A/dm~2,reverse current density6 A/dm~2,forward pulse time 150 ms,reverse pulse time 5 ms.Under the above conditions,the uniformity of TH is more than 80%,and the coating performance meets the requirements of industrial production.(2)The composition and structure of anode slime were analyzed,the forming conditions of anode film were studied,and the reaction mechanism between anode and plating solution was discussed.It is found that the anode slime mainly contains Cu,Cl,C,O,P and S elements,suggesting that the leveler does not participate in the process of anode film formation;electrochemical experiments showed that P in anode and Cl~-in plating solution are necessary conditions for forming anode film.Both inhibitors and accelerators participated in the film formation.The results show that pulse electrodeposition of copper is the key to the manufacture of HAR TH,and the additive formula and plating parameters are the main factors to achieve uniform electrodeposition.At the same time,anode also plays an important role in the whole process of electrodeposition.Controlling the reaction between anode and bath plays an important role in maintaining bath stability(additive concentration)and limiting by-products.