Optimize PCB pad design for mm-wave measurements

In this presentation we discuss the challenges imposed by measuring PCBs using commercially available mm-wave probes, like the Cascade ACP probes. To accomplish high quality measurements the transition between the probe tips and the test vehicles on the PCB must show a low loss and good matching over the desired frequency range. In the field of on-wafer probing the design of such transitions is a well investigated topic. However these results cannot be applied directly for PCB measurements due to the limitations introduced by the RF laminates and the corresponding manufacturing processes.
To overcome these limitations a new landing pad design for measurements from DC up to 100 GHz was derived. Using EM filed simulation, the structure was investigated and optimized. The different versions of the landing pad was manufactured to verify the results from the simulations. Additionally the impact of the manufacturing tolerances on the performance of the landing pad were investigated.
The conditions imposed by the PCB results in lower planarity and harder surface finish compared to on-wafer probing. Therefore, we examined the mm-wave probes over different measurement campaigns and monitored their performance