Investigation of the impact on the radio frequency (RF) behaviour of electrically conductive adhesives (ECAs) used in wafer-level packaging (WLP) of RF-MEMS

In this work, an anisotropic conductive adhesive (ACA), belonging to the family of electrically conductive adhesives (ECAs), exploited for the wafer-level bonding phase in packaging of RF-MEMS (MEMS for radio frequency passives), is investigated in respect to its influence on the RF behaviour of packaged Microsystem structures and CPWs (coplanar waveguides). The explored encapsulation solution is based on the wafer-level packaging (WLP) approach, in which the capping substrate (high-resistivity silicon—HRS) provided of vertical through silicon vias (TSVs) is bonded to an RF-MEMS wafer using ACA as adhesion layer. After bonding of ACA, conductive metal particles within the epoxy-based matrix either contribute to the electrical path formation or, when uncompressed, remain isolated. Influence of such floating particles on the RF performance of adjacent structures is investigated by means of finite element method (FEM) electromagnetic simulations. The results show that the influence of floating ACA conductive particles on the S-parameters of the targeted planar structures is rather limited up to 60 GHz.