Hybrid Printing for the Fabrication of Smart Sensors

Summary

Here we present a protocol for the fabrication of inkjet-printed multilayer sensor structures on additively manufactured substrates and foil.

Abstract

A method to combine additively manufactured substrates or foils and multilayer inkjet printing for the fabrication of sensor devices is presented. First, three substrates (acrylate, ceramics, and copper) are prepared. To determine the resulting material properties of these substrates, profilometer, contact angle, scanning electron microscope (SEM), and focused ion beam (FIB) measurements are done. The achievable printing resolution and suitable drop volume for each substrate are, then, found through the drop size tests. Then, layers of insulating and conductive ink are inkjet printed alternately to fabricate the target sensor structures. After each printing step, the respective layers are individually treated by photonic curing. The parameters used for the curing of each layer are adapted depending on the printed ink, as well as on the surface properties of the respective substrate. To confirm the resulting conductivity and to determine the quality of the printed surface, four-point probe and profilometer measurements are done. Finally, a measurement set-up and results achieved by such an all-printed sensor system are shown to demonstrate the achievable quality.

Introduction

Additive manufacturing (AM) is standardized as a process where materials are joined to make objects from 3D model data. This is usually done layer upon layer and, thus, contrasts with subtractive manufacturing technologies, such as semiconductor fabrication. Synonyms include 3D-printing, additive fabrication, additive process, additive techniques, additive layer manufacturing, layer manufacturing, and freeform fabrication. These synonyms are reproduced from the standardization by the American Society of Testing and Materials (ASTM)¹ to provide a unique definition. In the literature, 3D-printing is referred to as the process where thickness of t....

Protocol

CAUTION: Before using the considered inks and adhesives, please consult the relevant Material Safety Data Sheets (MSDS). The employed nanoparticle ink and adhesives may be toxic or carcinogenic, dependent on the filler. Please use all appropriate safety practices when performing inkjet printing or the preparation of samples and make sure to wear appropriate personal protective equipment (safety glasses, gloves, lab coat, full-length pants, closed-toe shoes).

NOTE: The protocol can be paused after any step except steps 6.3 - 6.6 and steps 9.2 - 9.5.

1. Preparation of 3D-printed Substrates

1. Prepare compu....

Results

From the SEM images shown in Figure 1, conclusions on the printability on the respective substrates can be drawn. The scale bars are different due to the different ranges of the surface roughness. In Figure 1a, the surface of the copper substrate is shown, which is by far the smoothest. Figure 1c, on the other hand, shows steel, a substrate which is not usable for inkjet printing due to the high poro.......

Discussion

A way to fabricate multilayer sensor structures on 3D-printed substrates and on foil is demonstrated. AM metal, as well as ceramic and acrylate type and foil substrates are shown to be suitable for multilayer inkjet printing, as the adhesion between the substrate and the different layers is sufficient, as well as the respective conductivity or insulation capability. This could be shown by printing layers of conductive structures on insulating material. Furthermore, the printing and curing processes for all layers was suc.......

Materials

Name	Company	Catalog Number	Comments
PiXDRO LP 50	Meyer Burger AG		Inkjet-Printer with dual-head assembly.
SM-128 Spectra S-class	Fujifilm Dimatix		Printheads with nozzle diameter of 50 µm, 50 pL calibrated dropsize and 800 dpi maximum resolution.
DMC-11610/DMC-11601	Fujifilm Dimatix		Disposable printheads with nozzle diameter 21.5 µm, 1 or 10 pL calibrated dropsize
Sycris I50DM-119	PV Nanocell		Conductive silver nanoparticle ink with 50 wt.% silver loading, with an average particle size of 120 nm, in triethylene glycol monomethyl ether.
Solsys EMD6200	SunChemical		Insulating, low-k dielectric ink which is a mixture of acrylate-type monomers. Viscosity is 7-9 cps.
Dycotec DM-IN-7002-I	Dycotec		UV curable insulator, Surface Tension: 37.4 mN/m
Dycotec DM-IN-7003C-I	Dycotec		UV curable insulator, Surface Tension: 29.7 mN/m
Dycotec DM-IN-7003-I	Dycotec		UV curable insulator, Surface Tension: 31.4 mN/m
Dycotec DM-IN-7004-I	Dycotec		UV curable insulator, Surface Tension: 27.9 mN/m
Pulseforge 1200	Novacentrix		Photonic curing/sintering equipment.
DektatkXT	Bruker		Stylus Profiler with stylus tip of 12.5 µm diameter and constant force of 4 mg.
C4S	Cascade Microtech		Four-point-probe measurement head.
2000	Keithley		Multimeter to evaluate the measurements using the four-point-probe.
Helios NanoLab600i	FEI		Focused Ion Beam analysis station which provides high-energy gallium ion milling.
SeeSystem	Advex Instruments		Water contact angle measurement device.
Projet 3500 HDMax	3D Systems		Professional high-resolution polymer 3D-printer. See also (accessed Sep. 2018): https://www.3dsystems.com/sites/default/files/projet_3500_plastic_0115_usen_web.pdf
Polytec PU 1000	Polytec PT		Electrically conductive adhesive based on Polyurethane, available
Microdispenser	Musashi		Needle for microdispensing.
Micro-assembly station	Finetech		Equipment for assembly of, e.g., printed circuit boards (PCBs) and placing of chemicals (e.g. solder) and SMD parts.