Electrical performance of the recessed probe launch technique for measurement of embedded multilayer structures

This paper explores the electrical performance of a recessed probe launch (RPL) technique for measurement of embedded (internal) printed circuit board (PCB) structures such as striplines and vias (plated through holes). The RPL uses high-frequency microprobes in combination with a milling technique that removes upper board layers and exposes internal probing points. A two-tier calibration technique is applied for the extraction of the S-parameters of the RPLs with the help of thru-reflect-line calibration standards designed on PCB. Full-wave models are used to corroborate and validate the obtained S-parameters. Good model-to-hardware correlation is obtained up to 40 GHz. Furthermore, the launch performance with respect to microprobe positioning and variations of the cavity size is investigated using the full-wave models. These simulations suggest techniques for launch optimization and probe modifications that improve the launch measurement bandwidth.