Ni-Au surface finish effects on RF performance

We present a simplified analysis of the Nickel-Gold surface finish effects on microstrip conductive losses for boards with different Ni thickness and Ni/Au finish chemistries. Otherwise identical test structures were fabricated with various Ni/Au finishes and different thicknesses. The conductive loss has been extracted from Q measurements on series microstrip resonators. A theoretical model for conductor loss of a two metal layer system has also been proposed. The theoretical approach has been supported with measurement results. For a specific frequency, conductive loss shows an S-curve behavior with Ni thickness.