Analysis of the three-dimensional delamination behavior of stretchable electronics applications

Stretchable electronics offer potential application areas in biological implants interacting with human tissue. Furthermore, they facilitate increased design freedom of electronic products. Typical applications can be found in healthcare, wellness and functional clothes. A key requirement on these products is the ability to withstand large deformations during usage without losing their integrity (i.e., large stretchability). One of the possible basic designs for stretchable electronics is to interconnect small rigid semiconductor islands with thin metal conductor lines on top of a highly deformable substrate, such as a rubber material. In this case, large stretchability must also be provided by these thin metal conductor lines. The adhesion of the conductor lines to the rubber substrate is of major importance from a reliability point of view. Experimental observations show that delamination between the metal conductor lines and the stretchable substrate may eventually lead to short circuits while also the delaminated area could result in cohesive failure of the metal lines. To understand and quantify the behavior of the copper-rubber interface, peel tests are performed and analyzed by means of experiments and numerical simulations. Interestingly, experimental observations show that the rubber is severely lifted at the delamination front caused by its high compliance. To quantify the interface properties, numerical simulations of the peel test have been performed by developing a finite element model comprising of cohesive zone elements by which the transient delamination process during the peel test is described in detail. By means of an extensive model parameter sensitivity study combined with the measured peel-force curves and the rubber-lift geometry at the delamination front, the final set of model parameters has been determined. Finally, the thus obtained model parameters are used to simulate the delamination behavior of actual three-dimensional stretchable elec- tronics samples loaded in tension.