Coaxial Wiring Structures in Printed Circuit Boards

We have developed a printed circuit board (PCB) technology with coaxial wiring structures. The coaxial PCB was designed for a prototype model in order to verify the high frequency and high-speed signal transmission characteristics of the coaxial wiring, where high frequency low loss dielectric material was used as insulation layer. It was fabricated by buildup PCB process, additionally using NC end mill router to make a vertical shielding wall electrode. The high frequency measurement of the fabricated coaxial PCB was carried out by the time domain reflectometry (TDR) measurement and the time domain transmission (TDT) measurements. The characteristic impedances of the coaxial wiring lines were evaluated using a TDR waveform analyzer. The average characteristic impedance was controlled within 54 Omega plusmn 3.7 %. The S-parameters were calculated from TDR/TDT measurement results. The insertion loss was measured to be less than 2.3 dB/cm at 10 GHz. Coaxial via structure was investigated for future multilayer coaxial PCB.