A new vertical transition for FR-4 based millimeter-wave MCMs

A new vertical transition is presented that enables the use of epoxy-resin (FR-4) substrates for multi-chip modules (MCM) at millimeter-wave frequencies. A short microstrip trace on an FR-4 motherboard is connected to standard WR-10 waveguide for integration with other system components (e.g. antennas). The microwave transition is accomplished within a small (3 mm by 4 mm) three metal layer miniature PCB that is placed on the FR-4 motherboard. The small size and simplicity allows the transition PCB, called a “transition block” to be fabricated at very low cost. The transition block is attached to the motherboard using a solder reflow process compatible with standard SMT manufacturing lines. Using this technique, less than 2 dB insertion loss with over 10 GHz bandwidth is predicted. Test structures were fabricated resulting in measurements that show good agreement with simulations.