Manufacturability of lab-on-chip devices : dimensional variation analysis of electrode foils using visual technology

Abstract

Electrodes are necessary components for measuring changes in electrical properties in many microfluidic devices. Daktari CD4 Cell Counter system utilizes an interdigitated electrode foil in order to measure the concentration of the CD4 cells in an assay chamber by measuring the impedance drop. Thus the consistency in the dimensions of the interdigitated fingers in the electrode is critical to the repeatability of impedance measurements. This work involved a thorough variation analysis of the electrode dimensions to characterize the repeatability of the new manufacturing process developed by Daktari. For this purpose optical imaging was used to obtain high-resolution images of the electrodes and an algorithm was developed in order to estimate the critical dimensions of interdigitated fingers from the images. The results showed that the dimensional variation in the electrodes had insignificant effect on the performance of the electrodes and that the new manufacturing process is capable of producing satisfactory electrodes within the desired target. The relation between the electrode's dimensional variations was found and the effect of critical process parameters was determined in order to maintain the process statistically in control.