Hybrid 3D Printing: Comparing High-Frequency Filters with Conventional Methods

In the recently published ‘High-Frequency Filters Manufactured Using Hybrid 3D Printing Method,’ authors Ubaldo Robles, Edgar Bustamante, Prya Darshni, and Raymond C. Rumpf outline the development of two varying devices. In using hybrid 3D printing, they employed both conductive inks and thermoplastic substrates, performing further research regarding the potential of 3D printing technology within electronics, and 3D circuits. They compared basic microwave filters, made both conventionally and via 3D printing.

The two designs are well-known overall, allowing the researchers to make true comparisons that other users interested in electronics can relate to. Filtering signals at 2.4 GHz, the devices were evaluated for performance:

“The conventional filters were manufactured as standard PCBs that utilized copper for the conductors and FR4 as the dielectric substrate. The hybrid 3DP filters had dispensed silver inks to form the conductors and acrylonitrile butadiene styrene (ABS) plastic as the dielectric substrate deposited via fused filament fabrication (FFF),” explained the researchers.

“Hybrid 3D printing was used to merge micro-dispensing and FFF into a single manufacturing process. Using nScrypt hybrid 3D printing technology, we were able to handle 3D printed features, accuracy, and repeatability down to the micron size level. Last, the devices were tested using an Agilent vector network analyzer (VNA), and the results compared show that this technology is able to form simple high-frequency circuits.”

The two designs consisted of a coupled-line bandpass filter and a stepped-impedance low pass filter. The authors explained that both were based on microstrip transmission lines, but with different dielectrics and different permittivity. The researchers adjusted the substrates as they attempted to meet ‘comparable performance’ of 2.4 GHz.

ANSYS simulation model for the low-pass filter.

For the bandpass filter, function was based on frequency selectivity of directional coupling. The researchers also found that the performance of the filter is considered negligible when spacing is less than 10 µm. Overall, this filter was meant to function at 2.4 GHz with a passband with fractional bandwidth of 10%.

PCB design of the bandpass filter.

The simple low pass filter was able to weaken signals above 2.4 GHz. The researchers found that the filter was easier to 3D print because the geometry was free of breaks and closely spaced lines.

PCB design of the bandpass filter.

The researchers used a nScrypt Tabletop series 3D printer—a hybrid printer, accompanied by silver conductive ink. Solidworks was used for design, and Slic3r for generating g-code.

Tool path for 3D printed bandpass filter

Print time for the low pass filter was one hour and 28 minutes. For the bandpass filter, which is twice as large, 3D printing took 3 hours and 6 minutes.

(a) PCB in contrast with (b) 3D printed filter

Numerous factors led to discrepancies:

• Conductivity of CB028
• Surface roughness of the 3D printed substrate
• Curing temperature for silver paste
• Lack of ability to adjust printing during the process

“We found that the lower permittivity of the ABS plastic led to designs utilizing a thinner substrate. Considering that 3D printing can produce structures with part air, we think 3DP can produce circuits that are smaller, lighter, and use less material to manufacture. This could have significant impact in volume manufacturing. We found it helpful to use thin paint films like polyurethane or epoxy to protect the printed conductors from oxidation. We also found it useful to incorporate features in the substrate that provide mechanical support for SMA connectors. There is a need to develop materials with lower loss, higher conductivity, and that are able to create smoother surfaces as they are 3D printed,” concluded the researchers.

“With further refinement in our 3D printing techniques, we conclude that direct-write 3D printing is a viable form of manufacturing for filter devices. Later, we envision filters being more 3D, arbitrary, and saving space and weight.”

Points of comparisons between devices produced by different manufacturing processes.

Hybrid 3D printing continues to gain traction—as users continue to want it all. Sometimes it takes a lot of experimentation, but progress within the digital fabrication realm continues to accelerate. Hybrid 3D printing is currently also connected with robotics, maintenance repair operations, and scalable systems. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.