Electrical characterization of adhesive flip chip interconnects for microwave application

Microwave performance of the anisotropic conductive film (ACF) and nonconductive film (NCF) interconnects was investigated by measuring the scattering parameters (S-parameters) of the flip chip modules employing the films. To compare the accurate intrinsic microwave performance of the ACF and NCF interconnects without lossy effect of chip and substrate, a de-embedding technique was employed. The effects of two chip materials, Si and quartz (SiO2), and of the metal pattern gap between the signal line and ground plane in the coplanar waveguide (CPW) on the microwave performance of the flip chip module were also investigated. The transmission properties of the quartz were markedly improved over those of the Si chip, which was not suitable for the measurement of the S-parameters of the flip chip interconnect. Extracted impedance parameters showed that the microwave performance of the flip chip interconnect with NCF was slightly better than that of the interconnect with ACF, mainly due to the inductive effect of the conductive particle surface and capacitance of the epoxy matrix in the ACF interconnect.