Study On High-speed Through-hole Copper Plating Of Printed Circuit Board

Copper plating is used for via metallization of printed circuit board(PCB) as its good electronic and thermal conductivity. With the rapid development of electronic industry, the size of PCB goes to smaller and smaller, the performance requirements are increasing. It shows finer lines on the PCB, higher aspect ratio and better stability. It makes scattered ability of the solution go down, via metallization becomes more difficult. In order to face the demand of PCB, we should rise the current density to shorten the plating time. Concentration polarization increased in the different areas of PCB under the high rate copper electroplating, it’s a new challenge. The electroplating requirements are well satisfied by develop new additives.The paper starts with mechanism of the additives, set up new method to evaluate the additives, and validated the accuracy of the method by experiment. The inhibitors can be qualitative and quantitative analyzed by cyclic voltammetry stripping, judge their performance difference by cyclic voltammetry(CV) curve similarity; compared CV curve of the solution to the standard curve, we can work out the concentration of the inhibitor. Cyclic voltammetry can be used for evaluating the performance of the leveler, if the copper deposition potential shifted toward negative greatly, it’s a good leveler. If the potential shifted above 30 mV after adding the leveler, it can be further test, the method can use for eliminating some poor leveler.The redox couple will react in the plating solution, they competitively consume the electric energy with copper ions to reduce current efficiency of copper plating, the throwing power improved as the current efficiency of the board and via reduced in different degree. This paper add ferric sulfate or benzoquinone respectively which contain redox couple, discuss their influences in the high rate electroplating solution. The result shows, trace iron ion can’t change the throwing power; benzoquinone will switch between its oxidation state and reduction state, impact the current efficiency and improve throwing power, so applied to the actual copper plating.The mechanism of the additives are different under different plating conditions. This article is optimizing concentrations of bath components by design of experiment method, adjusted them to an optimal parameter, and found that brighter is an important factor in high rate copper plating. The average throwing power of through holes is greater than 80% on the aspect ratio of 6.4:1 hole(d=0.25 mm) at control condition, and the microstructure of via is good. Finally change the current density and stirring intensity to study their functions. The copper deposition rate will be accelerated after improve the current density, but throwing power brings down; stirring will impact the mass transfer of cathode surface, thus improving the uniformity of current distribution.