Additive manufacturing with conductive materials enables new approaches to printed electronics that are unachievable by standard electronics manufacturing processes. In particular, electronics can be embedded directly into structural components in nearly arbitrary 3D space. While these methods incorporate many of the same materials, the new processing methods require standard test methods to compare materials, processing conditions, and determine design limits. This work demonstrates a test method to quantitatively measure the adhesion failure of printed inks deposited on a substrate without changing the ink printing conditions. The proposed method is an adaption of single lap shear testing in which the lap joint is created by bonding the second substrate to the ink after curing. It was found that the interfacial shear strengths are independent of the adhesives used to attach cured conductive ink to the second substrate. In addition, chemical surface treatments of flame and plasma and mechanical sand-blasting increase the interfacial shear strengths by ~25% and 80%, respectively, while altering the adhesive failure mode to cohesive failure for most cases. This work also shows extruded substrates with undulated features increase adhesion strength; therefore, in addition to surface treatments, the geometric freedom of additive manufacturing (AM) could be leveraged to design surface features for enhanced adhesion.

Additive manufacturing (AM) of electronics provides a route for creating customized systems with novel geometries that are not feasible with traditional methods. Standard AM processes such as extrusion can produce substrates on which electrical traces can be deposited. However, the surface roughness of plastic extrusion reduces the effective electrical conductivity and can introduce anisotropy, especially in radio frequency (RF) devices. The roughness can be reduced using vapor smoothing (VS), but solvent absorption changes the surface composition slightly, can be environmentally hazardous, and is not feasible with all thermoplastics. A new method introduced here—coined thermal smoothing (TS)—utilizes a heat source to locally reflow the material, thus minimizing the roughness of the undulating surfaces without the drawbacks of VS. This research work compares the surface roughness impacts of both smoothing processes with profilometry and scanning electron microscope (SEM) images. Both smoothing processes significantly reduce the surface roughness of extruded components by 80% and 90% for TS and VS, respectively. This paper also examines the influence of surface smoothing on high-frequency conductivity of microdispensed conductors (CB028 paste) deposited on the substrates. The measured loss on coplanar waveguides shows an improvement of up to 40% at 7 GHz.

The ability to fabricate functional 3D conductive elements via additive manufacturing has opened up a unique sector of ‘hybridized printed electronics’. In doing so, many of the rigid standards (i.e., planar circuit boards, potting, etc.,) of traditional electronics are abandoned. However, one critical challenge lies in producing robust and reliable interconnections between conductive inks and traditional hardware, especially when subjected to harsh environments. This research examines select material pairings for the most resilient interconnection. The method of test is wire bond pull testing that would represent a continuous strain on a connection and high acceleration testing of up to 50,000 g that would represent a sudden shock that electronics may experience in a drop or crash. Although these two environments may be similar to an overall energy exerted on the connection, the rate of force exerted may lead to different solutions. The results of this research provide insight into material selection for printed electronic interconnections and a framework for interconnection resiliency assessment, which is a critical aspect in realizing the production of next generation electronics technologies for the most demanding environments.

In this work, two AM technologies were utilized to compare the effectiveness of fabricating a simple electronic device with a conductive trace and hollow cylinder representative of ‘printed packaging’ that would survive harsh environmental conditions. The printed packaging cylinder delineates printed potting for electronics packaging. An nScrypt direct write (DW) system was the primary manufacturing system but a developing technology—coined large area projection sintering (LAPS)—manufactured a subset of samples for comparison. The tests follow Military Standard (MIL STD) 883 K and include resiliency evaluation for die shear strength, temperature cycling, thermal shock, and high G loading by mechanical shock. Results indicate DW Master Bond epoxy devices show resilience to extreme temperatures, thermal shock, and mechanical shocks while also surpassing the die shear strength failure criteria specified by the MIL STD. LAPS sintered Nylon devices also show mechanical resilience to thermal shock and surpass the die shear strength failure criteria. However, there were some open circuits, increases in resistance, and delamination when LAPS Nylon devices were subjected to extreme temperatures and 20 000 G shock loading normal to the substrate. The thermal effects are likely due to the thermal expansion mismatch between Nylon and the conductive paste while the mechanical shock effects may be attributed to the geometry differences of the LAPS Nylon printed packaging. Further studies are required to understand these failure modes in some of the LAPS Nylon samples and refine the process to address them.