Effects of pulse parameters on surface properties of silver coatings on copper substrates

Başaran, Caner
Electronic conductivity is a parameter that exhibits the free-electron transportation ability of a material. The radiation efficiency and insertion loss are directly related to the conductivity of the materials used in the systems like antennas, waveguides, power dividers, couplers, active circuit elements etc. operating at Millimeter-Wave (mmW) and Terahertz (THz) frequencies. The signal quality of systems operating at ultrahigh frequencies for the transmission of electromagnetic waves is very much dependent on the surface finish that has good conductivity. The use of pulse electrodeposition techniques causes homogeneous deposits of better surface quality than direct current techniques. The effects of pulse parameters on the surface quality of silver coatings on the copper base material in terms of scattering parameter (S-parameter) and surface roughness were analyzed in this study. Three pulse parameters which are duty cycle, frequency and average current density were selected to observe the effects on the surface quality of silver plating. It was analyzed that the increasing average current density has the effect of reducing surface roughness. Moreover, the surface roughness was reduced while increasing on time of the pulse current. Increasing the time differences between on time and off time also caused smoother surfaces. Relatively rough surfaces were observed at higher duty cycle and lower frequency. Furthermore, it was detected that frequency was less effective on surface roughness. As a result of (S11) measurements, it was observed that rougher surfaces have more return loss. Scanning Electron Microscope (SEM) was used to characterize the microstructure of silver plating. As a result of SEM analysis, pyramidal growth was obtained with pulse electrodeposition. Smaller grains and less porosities were detected with the increasing average current density at high frequencies and high duty cycles. Irregularity was observed in the grain structure with decreasing average current density. According to X-Ray diffraction (XRD) analysis, smaller silver grains were observed at high duty cycle, high frequency and high average current density. Effects of pulse parameters on the diffusion of silver into the copper base material were analyzed by Energy-dispersive spectrometer (EDS) line analysis.