Effect on Radio-Frequency Characteristics of Pad-to-Pad Interconnection by Varying Vertical Interconnect Density in Magnetically-Aligned Anisotropic Conductive Adhesive

In a magnetically aligned anisotropic conductive adhesive (MA-ACA), high-density vertical interconnects (VIs) are created by agglomerating micron-scale ferromagnetic particles in an epoxy medium through their magnetization process when a magnetic field is externally induced. In this paper, we characterize the radio-frequency properties of pad-to-pad transition created in an MA-ACA on small input and output (I/O) pads less than 100 × 100- μm. In order to analyze created VIs in an MA-ACA, an equivalent circuit model is suggested and validated by using a parasitic extraction approach from the measured S-parameter responses of a silicon-on-silicon test sample. In addition, the effects of the composing parasitics are investigated depending on vertical interconnect density (VID) by adjusting the weight fraction of loading conductive particles. Furthermore, based on a uniform-spacing distribution model of VIs, a failure rate of a pad-to-pad transition is estimated depending on I/O pad size. Experimentally, by refining loading conductive particles, the RF properties of a pad-to-pad transition on silicon test samples are demonstrated to be more consistent. Therefore, by characterizing the RF performance of a pad-to-pad transition depending on VID, a proposed RF packaging approach using an ACA is expected to be effectively applicable to high-density RF applications.