Behavior Research On Copper Electrodeposition In Solution Threading Through Hole For PCB

The requirements of functional integration and high performance of electronic products lead to miniaturization, functionalization and highly integration of their components support-printed circuit board(PCB). Through hole plating copper is one of the methods of high performance PCB interconnection, it’s quality has a direct impact on the electrical reliability and life of the product. With the increase of PCB integration and wiring density, the aspect ratio of through-holes(THs) is increased, causing low exchange rate of plating solution, thus resulting in asymmetrical plating thickness and the decrease of throwing power(TP). Thus, increasing the TP of through-hole plating copper has a great significance for promoting the development of PCB technology. In this thesis, in order to promote the TP of PCB micro-vias plating, an innovative copper electrodeposition device for high aspect ratio THs plating was invented and the copper electrodeposition behavior using this device was investigated.The plating uniformity and TP of micro hole are the foundation of excellent inter layer interconnection. The mass transfer behavior and the control of multi-physical field factors are the basic conditions to obtain high quality coating. New innovative copper electrodeposition device generated a forced convention for plating solution by gravity, which fundamentally changed the mass transfer process of plating solution during the electroplating process. The way of electrode placement and types of power supply were improved by this device to form evenly distributed multi-physics field effect such as the electric field, flow field, temperature field and magnetic field, thus improving the uniformity and TP of the micro hole. Compared with the haring cell, copper plating by the innovative copper electrodeposition device showed that: the TP of THs was improved 29.8%, which the aspect ratio of THs is 10.6(3.2:0.3); the TP of THs was improved 32.7%, which the aspect ratio of THs is 12.8(3.2:0.25). The TP of each aspect ratio THs was different but the difference was small, and the minimum difference was 0.7. A same result was investigated with the current density increasing. The TP of THs was improved 18.1%, which the aspect ratio of THs is 10.6. The TP of THs was improved 22.4%, which the aspect ratio of THs is 12.8.According to the electrochemical principle, the electrodeposition behavior of copper in the microhole is not only influenced by liquid mass transfer, electric field distribution, but also related to the forms and additives’ concentration in the bath. The effect of additives is more important for the requirements of high properties of excellent electrical and copper coating in the PCB. In this paper, the influence of the additive concentration and current density on the plating ability was studied by orthogonal experimental method. Additive concentration and current density distribution in the optimal bath were obtained The optimal liquid level difference is 2cm between inside and outside level, namely the flow rate is 0.5 L/min, the TP of THs is 79%, the morphology of THs is smooth and compact. The preferred orientation is(220). Additionally, in the system without leveling agent, the TP of the innovative copper electrodeposition device was obviously higher than that of Haring cell and the copper coating exhibited excellent morphology, structure and growth orientation.PCB manufacturing is a continuous process, and the accumulation of metal ions and other ions in the bath can affect the stability of the process, in which the Fe ion accumulation and behavior is of the most attention. In recent years, with the the use of insoluble anode titanium mesh, the accumulation and behavior of titanium ion and ammonium ion have attracted people’s attention. Experimental results showed that the iron ion couple could improve the TP and smoothness of copper layer, the TP of THs was increased from 70.9% to 76% while the aspect ratio of THs is 6.4(1.6:0.25), and the grain size of copper was reduced. Moreover, the components and the thermal resistance of electroplating copper layer were not affected, while the current efficiency was decreased and the energy consumption was increased significantly in the electroplating process; The current efficiency was slightly improved with the addition of Ti4+ in the plating solution but was not affected by the the addition of ammonium ions in the plating formula. Additionally, the current efficiency, TP and thermal resistance were not influenced by the titanium ions and ammonium ion, with smoothness improvement of the copper coating to a certain extent.The electrochemical behavior of iron ion was investigated by cyclic voltammetry in order to research the reasons of the effects on through holes plating by iron ion couple. Experimental results showed that the reduction reaction of iron ion couple at cathode would become competitive reaction of copper deposition, which would lead to the decrease of current efficiency and the promotion of throwing power; in addition, iron ion could’t affect the electrochemical behavior of additives.