In-situ laser sintering for the fabrication of fully 3D printed electronics composed of elastomeric materials

Abstract

In-situ laser sintering can be used to locally sinter conductive inks in an uninterrupted process, enabling the embedding of printed electronics within 3D printed structures. In this work we apply a laser sintering method to create highly conductive silver features (50-125 µΩ cm) on top of and embedded within thermosensitive polymers printed by fused deposition modelling (FDM). We exploit this method to locally sinter silver inks deposited by direct ink writing (DIW) without external processing. Furthermore, we perform this while thermally preserving the 3D printed thermoplastic polyurethane (TPU) substrate which has a low glass transition temperature. By analyzing the effect of the process for both small and large shapes of conductive features, we show the importance of the transmitted power and sintering time. Lastly, we apply the developed method to produce flexible conductors and sensors. These include pressure and bending sensors that could find their way into cost-effective and customized soft electronic devices.

Direct Laser Writing: From Materials Synthesis and Conversion to Electronic Device Processing

“…[17] Laser sintering for metal processing has become a straightforward alternative to access high-resolution writing of conductive lines and other geometries, not only improving film conductivity but also adhesion to support substrates. Besides glass, [101,102,105,137] other compatible substrates have been used, including semiconductor wafers (Si/SiO x , [102] ITO, [137] and GaAs), [138] ceramic surfaces, [139] and several flexible substrates (PI, [102,137,[140][141][142] PET, [143] PEN, [144] TPU, [145] and paper). [141,146] Different noble metal NP sources and other particle morphologies have been targeted, including gold, [21,102,147] silver, [101,147,148] and platinum.…”

“…Reproduced with permission. [145] Copyright 2021, IOP Publishing. lasers are needed, and absorbed photon energy must be enough to excite electrons from the ground to an excited state and promote reduction.…”

“…Cross-section of sintered film with different thickness, resulting in different sintering uniformity (h) and effect of laser writing speed on resistivity values of sintered silver films (i). Reproduced with permission [145]. Copyright 2021, IOP Publishing.…”

3D printed electronics with nanomaterials

“…405 Additional laser sintering of metal NPs can be applied. 288,406 While the binder-jet technique already uses ink-jet printing, the materials in one section of printing heads can be replaced with conductive inks or the AJP technique can be incorporated into the process. 132 As we saw previously in the section regarding 3D printing of biomedical sensors or lab-on-chips and in the large section of 3D printed electronics, the most obvious next step is the combination of both of them.…”

“…405 Additional laser sintering of metal NPs can be applied. 288,406 While the binder-jet technique already uses ink-jet printing, the materials in one section of printing heads can be replaced with conductive inks or the AJP technique can be incorporated into the process. 132…”