Air-gap transmission lines for multiprocessor interconnects on FR-4 and BT substrates

The fabrication and characterization of low loss parallel plate and microstrip lines with an air dielectric layer is described. The lines are characterized by capacitance and loss tangent at 10 kHz and 100 kHz and by S-parameters up to 10 GHz. The inclusion of the air-gap significantly reduced the loss tangent and lowered the dielectric constant to between 1.5 and 1.8. More complicated transmission line structures could be fabricated using the described techniques.