Electroless Metallization of Stereolithographic Photocurable Resins for 3D Printing of Functional Microdevices

Abstract

In the present paper the electroless metallization of 3D printed devices using stereolithography is investigated. Two different photocurable resins from a commercial supplier and a self-formulated one are used as starting materials for printing. A first metal layer of NiP or Cu, obtained by an optimized pretreatment and plating process, is subsequently applied on the parts. The possibility of obtaining multilayers through the successive electrodeposition of different metals on the electroless treated parts is demonstrated as well. From the applicative point of view, the use of 3D printing, coupled with electroless deposition of mono or multilayers, can be employed to manufacture functional microstructures for use in the fields of microrobotics, MEMS, metamaterials and others. For this reason, the realization of a prototypical magnetic actuator is presented as an example of possible application. 3D printing1 has recently acquired great relevance for research and industrial applications due to its advantages with respect to traditional manufacturing techniques: the opportunity to create geometries impossible to obtain with other techniques, low cost and great scalability. This technique has been applied in the past for both rapid prototyping and production of custom-made parts.2,3 In recent years, thanks to the introduction of techniques able to operate at the microscale, new possibilities have been individuated in fields like microrobotics, MEMS or metamaterials fabrication. Many 3D printing techniques are available, such as stereolithography (SLA), 4 Selective Laser Sintering (SLS), 5 Fused Deposition Modelling (FDM) 6 or Two Photon Lithography (2PL). 7 Techniques like SLA or 2PL present however significant advantages compared to FDM or SLS when the production of micrometric parts is required. In particular, the products are characterized by an improved surface finish and by the possibility to achieve great resolution; 8 dimensional tolerances are better than FDM or SLS printing. These important properties allow thinking to applications like the direct printing of microstructures that typically present characteristic dimensions in the order of μm, like MEMS or others.All 3D printing techniques able to operate at the microscale are however characterized by the same problem: metal parts are considerably hard to obtain. The materials used in 3D printing are mainly polymers and only some techniques are suitable for direct metal forming, like SLS.5 A possible solution to obtain a metallic finish on a printed object is to metallize only the surface of the resin. This makes possible to obtain some properties of metals without having a bulk metallic object. 9 In particular it can be convenient to use electroless plating, 10 a method able to provide thick and uniform metal layers on non-conductive substrates, such as the resins used in the printing step. By examining the existing scientific literature, it is evident that typical polymers used in FDM printing, such as PET, 11 ABS, 12 PLA and PETG 13 can be easily metalli...

Design, Fabrication and Testing of the First 3D-Printed and Wet Metallized z-Axis Accelerometer

“…In order to accomplish polymer conversion, the SL-printed models were post-cured for 15 min. Metallization of the samples has been performed employing a process already developed [3]. After the application of a first electroless Cu layer of 0.5 µm, a second 1.5 µm layer of electrolytic Cu was deposited.…”

“…In this work, a polymeric z-axis accelerometer is fabricated by means of SL and wet metallization that provides surface conductivity, which is necessary to obtain a capacitive readout of the z-axis accelerometer [3]. The proposed device has dimensions in the order of hundreds of µm and constitutes a first step towards the realization of 3D printed accelerometers, which may represent an alternative to MEMS-based devices in applications where miniaturization is not mandatory while customization is desirable.…”

Hard-magnetic cell microscaffolds from electroless coated 3D printed architectures

“…NiP was therefore deposited on CoNiP according to a methodology already used. 41 Final thickness was found to be 1.1 mm and the phosphorus content to be 2.5 wt%.…”

“…Properties of the first Cu layer, deposited on DL260, have been investigated in a previous work. 41 The mean thickness of the coating, as a consequence of the low temperature used during the deposition, was found to be around 400 nm. Adhesion to the substrate, qualitatively evaluated by means of a peel test, was found to be good.…”

“…A temperature below or equal to 45 1C is necessary due to the physical properties of the DL260 resin, which present a glassy transition around 50 1C. 41 Conversely, temperature should be as high as possible to allow high deposition rate. For these reasons, a temperature slightly lower than 50 1C was selected as optimal.…”