Aerosol Jet® printing of micro silver tracks on stereolithography resin

Additive manufacturing (AM) techniques are especially useful for producing prototypes, single-pieces or small series of products, because AM allows for a fast transfer from CAD model to physical product. Nevertheless, current AM technologies are mostly constrained to producing mechanical parts, with no extra functionalities. A next frontier is producing multifunctional AM products (electro-mechanical, electro-thermal…) by combining different AM techniques and their specific advantages. Stereolithography (SLA), for instance, is a well-established additive manufacturing process able to produce solid models and objectives by selectively photo-solidifying thin layers of UV curable materials, one on top of the other. On the other hand, Aerosol Jet® printing (AJP) shows its competitive advantage in printing interconnection, passive- and active components and antennas on glass or flexible substrates, as polyimide foil. By depositing AJP micro conductive traces in between SLA layers, electrical properties to SLA parts can therefore be added, and high functional, fully integrated devices could be realised in the next future. The low surface roughness of SLA layers will also assure repeatable surface conditions, making easier to print tracks in a repeatable manner. In the present work, this concept is further studied, and the feasible combination of stereolithography with aerosol jet® printing is investigated in detail. The conductive traces are created by depositing commercial silver ink using the AJP process. Experiments are conducted on a M3D Optomec AJP machine, and the deposition is made on partially polymerized UV – curable Somos SLA acrylics. Partial polymerization of the SLA substrate is specifically selected to exploit the higher surface energy of the resulted layer, thus allowing better wettability when liquids are deposited onto the surface. The degree of polymerization can be adjusted by tuning the exposure time or laser intensity, during the SLA process, and it represents a critical parameter. In the presented experiments curing time of the SLA material under the same lighting conditions is adjusted to find the optimal wetting properties. Insufficient curing, in fact, would cause deformation of the surface when the silver ink is deposited onto the surface. The large set of AJP process parameters (gas flows, temperature setting, printing speed, etc.), with effect on the material output rate, ink- and aerosol properties, were also considered during investigation. According to the first data obtained, the temperature of the aerosol before it enters the printing head seems the most important AJP parameter in this research. By increasing the aerosol temperature, more solvent evaporates before the ink is deposited onto the substrate. This allows for dryer printing of the ink and it decreases the surface tension of the deposited droplets, which will allow the printing of continuous lines with less interruptions. On the other hand, when temperature is set too high, the ink dries too fast also causing interruption of the printed track. Finding an optimum between curing rate and AJP settings is therefore crucial in stable deposition of silver ink onto partially polymerised UV material.

ISBN:9780956679024

Publication year:2013