Impact of 3D Printing Infill Patterns on the Effective Permittivity of 3D Printed Substrates

3D printing can potentially transform traditional electronics manufacturing by allowing for the accurate direct digital manufacture of complex electronic structures with a much smaller process footprint. However, there are challenges which restrict the use of 3D printing for electronic manufacturing. One significant challenge is the characterization of the electromagnetic properties of the 3D printed materials such as their resultant dielectric permittivity. This work reports on the investigation of existing mixture models to establish their suitability for predicting the dielectric permittivity of 3D printed binary materials for the test frequency range of 1 GHz to 10 GHz. The identified models included volume fraction mixture models which considered the material volume concentration of the binary material and shape factor mixture models which consider the geometry and distribution of the mixture constituents. The fused filament fabrication 3D printing process was used for this work. 3D printed samples were produced with varying percentage volume compositions and varying infill patterns. The dielectric permittivity of the samples was investigated using the two-layer stripline measurement method and the measured data compared to the mixture model estimates. The shape factor mixture models were found to not be in good agreement with the measured values of dielectric permittivity. This result was attributed to the relatively small size of the discontinuities within the 3D printed substrate being insufficient to present anisotropy relative to the wavelength of the applied test signals. The volume fraction models were found to be in close agreement for samples with select infill patterns.