Capacitive touch sensor for packaging application

Abstract

Low cost, fast and accessible electronic circuits can be fabricated on light-weight stretchable substrates. The integration of functional conductor on 3D (printed) complex geometries by vacuum forming techniques has potential for packaging applications. The Fujifilm Dimatix DMP-2800 inkjet printer is easy to use and very cost-effective. However, ink formulation is complicated and the property window for jettability is small. When formulating a functional ink, it is therefore important to tune all parameters (e.g., viscosity, surface tension, and density) such that a jettable ink is achieved [1]. In this study CleviosTM PH1000 (polymer-based PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate)) was applied to achieve a stretchable and conductive ink. The different parameters of the ink were adjusted by mixing dimethyl sulfoxide (DMSO) and PEDOT:PSS in different proportions. Jettable inks were printed on a thermoplastic polyurethane film (TPU) in different configurations. The printed layers were sintered in an oven at 110°C for 10 minutes. The printed films were subsequently characterized for sheet resistance, transparency and stretchability. Sheet resistances as low as 1100 Ω/sq were measured by Van der Pauw when only one layer was printed. By printing more than one layer, the sheet resistance could be reduced to 150 Ω/sq. To show its applicability towards 3D integration for packaging applications, the printed layer was stretched and integrated on a cone by vacuum forming (Fig. 1). The resistance change upon stretching was investigated and shows promising results. It can be concluded that the developed inkjet printable and stretchable conductor shows the capability to be formed around 3D parts, which can be useful for innovative 3D-packaging applications.