The number of processes and materials available for use in 3D printing systems for electronic and mechanical products is already extensive, and the options available for product designers is continuously expanding. When it comes to new electronic devices, specifically PCBs, the materials that can be used in any new device depends on the specific additive manufacturing process used for fabrication.
This means that designers need to consider the process they wish to use for fabrication during the design phase, which will also place some limitations on the device architecture. Processes for depositing metals typically proceed at high temperature, or they require the use of a laser to fuse materials into a solid conductive element. These other processes may not be the best option for PCBs, depending on the substrate, desired throughput, and device architecture.
TEM image of gold nanoparticles
As a new class of materials for additive manufacturing of electronics, conductive inks have advantages and disadvantages that need to be considered during the design phase. The mechanical and electrical properties of conductive inks after fusion will affect the range of applications for a finished device. However, conductive inks have simple formulation procedures and are immediately adaptable to existing printing processes, making them an attractive choice for 3D printed electronics.
What Are Conductive Inks for 3D-Printed PCBs?
Conductive ink is simply a suspension of metal nanoparticles in a host liquid. Nanoparticles in solutions can agglomerate over time into larger clusters. Thus, these nanoparticles are conjugated with a ligand to prevent them from clustering in the suspension. The choice of ligand and the host liquid will affect the viscosity of the suspension and its hydrophilicity on a substrate. These points need to be considered when selecting a substrate for use with conductive inks and the appropriate deposition process.
Once this nanoparticle suspension is deposited, the suspending liquid needs to be evaporated and the metal nanoparticles must be fused into a solid conductor. This can involve a high-temperature process, such as annealing, or a lower-temperature process, like optically-assisted sintering and UV exposure. There are other aspects of material selection that should be considered when determining if conductive inks are appropriate for your device and fabrication process.
Conductive Inks Advantages and Disadvantages
The primary advantage of using conductive inks in 3D-printed electronics is their flexibility. They can be deposited on a variety of planar or non-planar substrates. Conductive inks are also adaptable to inkjet printing or aerosol jet printing. The effect on the substrate should be considered when determining whether a conductive ink is appropriate. Ceramic or other rigid substrates can accommodate a higher temperature process without degrading, while a polymer substrate typically requires a lower temperature process.
Conductive inks can also be prepared from a wide range of metal nanoparticles. As long as the nanoparticle can be conjugated with an appropriate ligand, the viscosity and hydrophilicity of the ink can be adapted to the deposition process through the use of an appropriate suspending liquid, as well as any additives or surfactants.
Although metal nanoparticles of various shapes and sizes are commercially available, not all additive manufacturing systems are adaptable to all metals, and suppliers of these systems may not provide guidance on how to adapt different metals to their systems. In inkjet printing and aerosol jet printing, the ligand that is used to prevent agglomeration is critical to ensuring the print nozzle does not get clogged during fabrication. At a minimum, the ligand would need to be exchanged prior to deposition, which increases the costs associated with these already expensive materials.
Therefore, systems suppliers spend a considerable amount of time tuning these materials for use with their systems, and it can be difficult for a third party to formulate a new conductive ink for use with these systems. However, the additive manufacturing space is still an emerging area, and the range of available materials is only expected to expand going forward.
One aspect of conductive inks that can be seen as a disadvantage relates to the melting temperature of the metal nanoparticles. The melting point of metal nanoparticles tends to be inversely proportional to the particle size, which needs to be accounted for in the fabrication process. If the processing temperature is too low for a particular conductive ink, then the particles will not fuse into a continuous solid film, and any remaining structural defects in the film can decrease its electrical conductivity and mechanical strength.
Inkjet printing system for use with insulating and conductive inks
Conductive Inks in Inkjet Printing
The use of conductive inks for inkjet printing is a notable advance in additive manufacturing for electronics. Because the temperature of the fabrication process can be quite low and fusion can be optically-assisted, conductive inks are immediately adaptable for use in inkjet printing systems that can co-deposit conductors and the substrate simultaneously. This is a major advantage over other processes like aerosol jet deposition, laser direct structuring (LDS), or fused deposition modeling (FDM).
Simultaneous deposition of conductive ink and a polymer dielectric substrate, followed by simultaneous curing with high-intensity lamps, provides a much higher throughput than aerosol jet deposition, FDM, LDS, or similar processes. This allows a PCB to be deposited in a layer-by-layer process, making inkjet printing a natural choice for fabricating multilayer PCBs with planar or non-planar geometry.
The flexibility offered by inkjet printing and co-deposition of conductive inks and a polymer substrate gives designers significant freedom to create PCBs with unique architectures. Multilayer interconnect geometries are not limited to the traditional trace and vertical via structures used in PCBs on FR4, and conductive components like antennas, sensors, or inductors that can be easily deposited with non-planar geometry. Designers that use this type of system are freed from the constraints imposed by traditional PCB manufacturing processes.
Even though conductive inks have advantages and disadvantages, they are a great material to use for new 3D-printed electronic devices with unique geometries. The DragonFly LDM Lights-Out Digital Manufacturing System from Nano Dimension is uniquely adapted for 3D printing with this material. You’ll have plenty of freedom to design unique devices with planar or non-planar architecture. Read a case study or contact us today if you’re interested in learning more about the DragonFly LDM system.