Novel PDMS(silicone)-in-PDMS(silicone): Low cost flexible electronics without metallization

Future electronics will undoubtedly require natural integration at the system, device and package level in the form of a functional, flexible package. Functional, flexible electronics expand the functionality of devices allowing morphological-electronic response for ergonomic and natural interfaces between the device and its surroundings. Recent technological successes have been able to fabricate functional, flexible electronics, however have all failed to develop a package capable of meeting the stringent cost, reliability and performance required of consumer electronics. We demonstrate the application of electrically conductive adhesive technology to produce low cost, flexible electronics without metallization. We have shown the capability of fabrication of highly conductive Poly(dimethlysiloxane) (PDMS) (ρ~7×10−4 Ω•cm) by incorporation of 80 wt% bimodal distribution of micron sized silver flakes. PDMS is both the ideal substrate and composite matrix material due to its unique properties; PDMS is optically transparent, viscoelastic, chemically and thermally stable, highly flexible, hydrophobic and can easily be molded with high resolution and aspect ratio. These unique properties of PDMS allow for high resolution molds to be prepared from photolithographically defined substrates. Screen printing of electrically conductive PDMS into these molds with micro-sized features creates a low cost, flexible electronic package. We have coined this package PDMS-in-PDMS. We show that PDMS ECA can be prepared by curing a novel formulation of PDMS at curing temperatures of 150 °C for 15 minutes. Upon curing, the ECA undergoes a transition from insulating to conductive. TMA results have shown that this transition is due to ECA shrinkage >20%. Furthermore, we show simultaneous conductivity and tensile strain measurements to show the electrical properties of PDMS ECA are unaffected by tensile strains of >40%. We show the feasibility of this technology to create low cost, flexible devices without the need for metallization.