This paper presents the characterization of a PCI-Express test fixture that was created to passively probe a x16 link on a PCB. This fixture plugs into the 48-pin, midbus footprint that has been adopted by as the industry standard for observing PCI-Express links on a PCB. This fixture is used to passively probe signals and pass them to a piece of test equipment (TDR, VNA, or oscilloscope). Engineers reading this paper will be exposed to how a microwave test fixture with a high-density interconnect was designed, measured, and modeled, which ultimately resulted in the performance specifications of the fixture.