Some considerations of via stitching impact on parasitic coupling of RF multiports in multilayer packages and MCMs

Electromagnetic cavity-resonance modes in parallel-plate planes of power and ground rectangular structures along with parasitic coupling between excitation RF multiports are investigated. Such structures are widely used in microwave multilayer packages, MCMs and could be the source of considerable electromagnetic interference (EMI). Effective methods should be applied for damping and elimination of the radiated fields, especially in small areas and volumes. The investigated three-layered LTCC microwave package (QFN-type) possesses two separate grounding planes on different levels, connected through multiple shielding vias. The estimation of the electromagnetic field distribution is conducted by full-wave analysis of the proposed cavity-resonance models and corresponding S-parameters are extracted. This paper also discusses the influence of matrixlike via grid distribution on the propagation constant and effective dielectric permittivity of exemplary structures in the frequency band of interest -10 to 30 GHz.