  We develop a high speed on-chip flux measurement using a capacitively shunted
SQUID as an embedded cryogenic transducer and apply this technique to the
qualification of a near-term scalable printed circuit board (PCB) package for
frequency tunable superconducting qubits. The transducer is a flux tunable LC
resonator where applied flux changes the resonant frequency. We apply a
microwave tone to probe this frequency and use a time-domain homodyne
measurement to extract the reflected phase as a function of flux applied to the
SQUID. The transducer response bandwidth is 2.6 GHz with a maximum gain of $\rm
1200^\circ/\Phi_0$ allowing us to study the settling amplitude to better than
0.1%. We use this technique to characterize on-chip bias line routing and a
variety of PCB based packages and demonstrate that step response settling can
vary by orders of magnitude in both settling time and amplitude depending on if
normal or superconducting materials are used. By plating copper PCBs in
aluminum we measure a step response consistent with the packaging used for
existing high-fidelity qubits.
