2.?Experimental Procedure2.1. FabricationThis study used commercial PI films and screen printing technology to design and fabricate a flexible large area electronics sensor. PI films with copper foils are widely used in flexible electronics sensors for flexible printed circuits [26-28]. The PI film’s mechanical hardness and stress characteristics are about 0.181 GPa, and 87.14 MPa, respectively [29]. The sensor structures mainly include two PI films, one cover layer, and bump protrusions. Two PI films were used as the top and bottom films of the flexible electronics sensor. The top film contains the row electrodes, the organic resistance layers, and the bump structures. The bottom film includes the column electrodes and a cover film, which was laminated into the PI film using hot pressing to form the post layer for supporting the membrane of the top film.

The fabrication process mainly used a Model EKRA-E1 screen printer (Ekra, Japan), for printing materials on a flexible substrate. During the fabrication process, materials were transferred onto a substrate using a squeegee via an attached stencil mask. The fabrication process was carried out as shown in Figure 1.Figure 1.Fabrication procedures of flexible electronics sensors for large area manufacturing using screen printing technology.First, the electrode patterns on the bottom film with a 12 ��m copper foil (I), were defined for column and sensing electrodes using the photolithography method. The bottom film was then put into a solution of CuSO4 for electroless plating of Au, to a thickness of about 5 ��m, to avoid the oxidation of the copper foil.

Next, a cover layer with lattice patterns was laminated on the bottom film using hot pressing to form post structures (II). The hot-press process was performed at a temperature of 180��C for 20 minutes.The second part of the top film, which contains the row electrodes (i), is similar to that of the bottom substrate, except that it has pass-through holes that were drilled using the punching method. Cu was coated on the side of these holes using a chemical plating to transfer the output signal from the back to the top view of top film. An organic resistance material (ii), Model EPO 4X330, with a viscosity of 8 �� 104cp and a glass transition temperature of 190��C, was printed on sensing electrode areas using a screen stencil mask.

The organic resistance was synthesized using a phenolic resin, organic solvents, filler, and carbon black. The phenolic resin is a bisphenol A (C15H16O2) type of organic compound with two phenol functional groups. The organic solvents included Drug_discovery dimethylformamide (formula C3H7NO) and diethylene glycol monobutyl ether (formula CH3CH2OCH2CH2OCH2CH2OH). Dimethylformamide (N,N-dimethylformamide), is a hydrophilic aprotic solvent of the organic compound material that facilitates chemical reactions by polar mechanisms.