Numerical and experimental analysis of stretching induced interconnect delamination for stretchable electronic circuits

Stretchable electronics facilitate increased design freedom of electronic products. Representative applications can be found in health care, wellness and functional clothes, integrated electronics in stretchable parts and products. Typically, small rigid semiconductor islands are interconnected with thin metal conductor lines on top of a highly deformable substrate, such as a rubber material. A key requirement on these products is the ability to withstand large deformations during usage without losing their integrity (i.e., large stretchability). During stretching, the adhesion of the interconnects 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 characterize the copper-rubber interface, peel tests are performed. Experimental observations show that the rubber is severely lifted at the delamination front caused by its high compliance. When using the Environmental Scanning Electron Microscope (ESEM), actual fibrillation of the rubber at the peel front is observed at the micron scale. To quantify the interface properties, numerical simulations of the peel test have been performed by applying cohesive zone elements that describe the transient delamination process. The interface toughness is determined from the global parameters (i.e., forces and displacements) while the interface strength is defined by the local parameters (i.e., deformed rubber geometry at the delamination front and interconnect deformation). The thus quantified interface parameters are used to simulate the delamination behavior of a zigzag patterned interconnect three-dimensional structure. Furthermore, extensive in-situ failure mode analyses performed in scanning electron microscope are carried out. The occurring deformation behavior and failure mechanisms are characterized and used to validate the numerical model results