Measurement of Electrical Conductivity of Direct Digital Printed Conductive Traces Using Near-Field Microwave Microscopy

Non-contact measurement of electrical conductivity of direct digital manufactured traces using a dielectric resonator-based near-field microwave microscope (NFMM) operating at 5.73 GHz is reported. The NFMM uses a set of printed samples with known conductivity to build a calibration data set which correlates measured quality factor (Q) data with electrical conductivity (σ). Direct print additive manufacturing is used to produce the 10 mm x 10 mm calibration samples using CB028 silver ink and glass as the substrate. Conductivity of calibration samples ranges from 1.70e6 S/m to 3.22e6 S/m and it is measured using a commercially available four-point probe. Conductivity measurement of the calibration samples using NFMM reveals that the microscope is sensitive to printed samples with different conductivities and that it is able to resolve differences in conductivities as small as 0.38e6 S/m in the range 2.20e6 S/m ≤ σ ≤2.53e6 S/m. Conductivity and topography images of a printed trace are acquired simultaneously over a scan area of 100 μm x 100 μm using the non-contact NFMM at a distance of 3 μm from the sample. Conductivity images reveal that the conductivity is not constant over the scan area and that it varies from 0.6 S/m to 2 S/m. Roughness calculated from NFMM topography shows good agreement with the values computed from profilometer data.