Influence of a floating plane on effective ground plane inductance in multilayer and coplanar packages

The impact of a floating metal layer on the effective ground plane inductan ce has been investigated in Both multilayer (ground planes) and coplanar (g round conductors) packages. For the multilayer case, both thick and thin fi lm geometries were examined, and the results were compared to a thin film c oplanar configuration. It was seen that the floating plane actually increas es the ground plane inductance in the multilayer case and decreases the gro und plane inductance in the lead frame case. Examining the current density in the floating and ground plane and the ground's partial self-inductance a nd ground-signal partial mutual inductance give a detailed explanation for this phenomenon.