A study of copper thickness distribution in electroplating of printed circuit boards

Abstract

Copper electroplating is a very critical process for the printed circuit board (PCB) industry and it is increasingly important to maintain an even copper deposition over the PCB surface as circuitry design gets finer and denser. Although there has been considerable amount of research efforts to enhance plating quality of PCBs over the last few decades, most of the studies still rely on relatively small or laboratory scale experimental set-up. With the collaboration of a local PCB manufacturer, the project has made an important attempt to study the copper deposition behaviour in an industrial tank with a plating window of 144 inches. An industrial copper electroplating tank was designed and set up in the project such that seven hardware factors can be varied and their effect on copper deposition distribution can be examined. In the study, the Taguchi methodology was employed to examine the effect of plating tank design and configuration including anode geometry, anode distribution, electrode separation, relative size of the electrodes, cathode oscillation velocity, eductor orientation, eductor flow rate, and the current density on copper thickness distribution. Two consecutive sets of Taguchi design of experiment (DOE) were carried out for both planner and pattern substrates PCBs, in which a total of 58 industrial scale experiments were carried out. The mean response of each factors were examined, and the experimental results showed that the copper deposition evenness can be improved using the enhanced hardware settings for current densities commonly used in the PCB industry. Strong interactions demonstrated that previous result or models based on a laboratory scale set-up may not be applicable to full scale production. The Copper thickness distribution along the 144" PCB cathode was also studied from top to bottom and from one end to the other, and the edge effect was examined. The significance of the findings to the PCB industry was discussed and the outcomes of the project have led to a good foundation for further theoretical investigations.