Attenuation in silver-filled conductive epoxy interconnects

The attenuation of microstrip transmission lines fabricated with a new type of multiphase epoxy adhesive, called area bonding conductive (ABC) adhesive, has been measured from 45 MHz to 10 GHz. This ABC adhesive consists of a silver flake fill in a polymer matrix, and allows for both thermal and electrical conductivity in addition to increased strength. The board processing details are discussed along with the screen printing procedure. A technique for extracting the attenuation and sheet resistivity is presented which is based on network analyzer measurements of the S₂₁ scattering parameter. The performance for three different concentrations of silver flake in the conductive epoxy is compared with copper microstrip. There is a significant decrease in attenuation and sheet resistance as the concentration of silver increases, but in all cases the attenuation is a well-behaved function of frequency. Also, it is shown that microstrip transmission lines fabricated using stencil printing perform better at high frequencies than those made from screen printing