The Army Aviation and Missile Research, Development, and Engineering Center (AMRDEC) Weapons Development and Integration (WDI) Directorate has a program known as PRIntable Materials with Embedded Electronics (PRIME2). PRIME2 will integrate RF and electronics into additive manufacturing processes to reduce size, weight, and overall cost of these components and subsystems. This program will advance the state of the art in printable electronics, and deliver a materials database, process development, modeling, and simulation of 3D-printed objects with embedded conductive elements, passive prototypes, and RF prototypes. PRIME2 will create a new fabrication capability (applied to electronics and RF technology areas), weight reduction, higher reliability, and on-demand (local and immediate) spare components in the field.

Additive Manufacturing

Figure 1. Structures printed using PLA.

Additive manufacturing is a rapidly maturing process by which digital 3D design data are used to build up components in layers by depositing materials, or through the melting and sintering of (powdered) materials to create solid structures. These materials can be conductive (metal) or nonconductive (polymer), and have complex material properties that are dependent on print parameters.

Recently, additive manufacturing has quickly gained adoption and acceptance as a valuable manufacturing technology. There are many different types of printers, including fused filament deposition (FFD), stereolithography (SLA), and laser sintering. The National Aeronautics and Space Administration (NASA) has a FFD machine on the International Space Station (ISS).

Additive manufacturing, known as 3D printing, is rapidly developing to meet the needs of a wide range of commercial and military applications. 3D printing is typically used in prototype development to reduce costs and development time compared to traditional manufacturing. For example, 3D printing enables concept-to-prototype in less than a day at $5 to $8 per cubic inch of material, and it has been used to fabricate prototypes, tooling, fixtures, and forms to test design fit. 3D printing allows free complexity and integration of parts that are too costly or even impossible for traditional manufacturing. In some cases, printing requires no tool adjustments to fabricate hollow and buried structures; therefore, interconnects and connectors are simply printed where they are needed within the volume. This design freedom is particularly relevant to RF antennas where directivity and efficiency are currently limited by manufacturing constraints and losses in conductive feeds.

Figure 2. ABS polymer filaments.

Additive manufacturing brings a new capability that can be explored across all technology areas for benefits and use. The benefits can be many and varied, resulting in components that are not achievable utilizing traditional subtractive machining methods, lower-weight components, low cost, local and immediate prototyping, and component creation.

Traditionally, electronic components and RF components are assembled piecemeal and are not part of the additive manufacturing process. PRIME2 is developing enabling technologies to print an entire printed wiring board with embedded passive components and integrated RF structures in one step.


A variety of materials are available for additive manufacturing. These include both conductors and dielectrics; however, many of these materials compromise mechanical or electrical performance to enable ease of manufacture. In addition, many of these materials often require incompatible post-processing, such as thermal cures that can disrupt underlying structural elements. The characterizations of FFD (also known as Fused Deposition Modeling (FDM)), SLA, inkjet deposition, and microdispensable dielectric materials are presented here, along with the characterizations of FDM, inkjet deposition, and microdispensable conductive materials.

More than 35 dielectric materials suitable for FDM, SLA, and inkjet were evaluated in an effort to demonstrate a material set that had sufficient process compatibility to be co-fabricated that yielded electronic structures embedded within structural elements, yet also possessed sufficient performance to enable high-frequency RF use.

For dielectrics, relative permittivity and loss tangent are critical for implementing RF systems. In general, most additively manufacturable materials are polymeric, with a dielectric constant that falls within the range of 2 to 6; however, some unique materials are available. In particular, composite materials incorporating metals and ceramics provide enhanced dielectric constants that may be useful in RF design. Some polymer matrix composites can yield low levels of conductivity. These levels are not sufficient for quality RF components, but could be useful for direct current (DC) signals.

The selected conductive materials focused on inkjet and microdispense technologies. These materials demonstrated a wide range of conductivities. Organic conductors were at the low end of the range, and were not suitable for RF applications. Conductive epoxies have desirable features of room-temperature curing. This makes them more readily compatible with other additive manufactured substrates, but their conductivities were an order of magnitude below the nanoparticle inks that are used in aerosol and inkjet techniques. The nanoparticle inks exhibit no better than 50% of the conductivity of solid metal conductors such as electroplated copper. In addition, they require elevated temperatures to sinter the nanoparticles into a conductive sheet. These elevated temperatures can cause incompatibility with certain additively manufactured dielectric materials.

Based on the collected data, a subset of materials was further investigated for co-fabrication and realization of RF structures. Considerations during the selection process included material performance, material compatibility, availability and capability of additive manufacturing tools, and the desired RF component and designs.