Revisit nickel characterization effect on high-speed interconnect performance

It has been observed some surface finish like nickel-gold plating has exhibited significantly higher losses than expected on high speed interconnects like PCB trace and packaging. The investigation has revealed that this extra loss is resulted from the ferromagnetic characteristic of nickel material with large resistivity and non-unit frequency-dependent relative permeability. As a result, high-speed PCB design must take into account of the board surface finish effect, solder-mask coating and the physical geometry deformation of copper related to the etching process when modeling the PCB trace, which can be accomplished by using 3D-electromagnetic field simulation tools. Simulation results are correlated with the Vector Network Analyzer (VNA) measurements on several test cases and also on the actual application boards. In our experimental studies on the PCB test structures with ENIG and electroplated nickel-gold plating, there is no observation of the resonating anomalies in the insertion loss and group delay related to nickel permeability.