Analysis Of Interface Damage Behavior Of Flexible Substrate-metal Film Structure

The flexible substrate-metal film structure is the most basic structure in the field of flexible electronics.It usually assumes the role of metal wires and metal electrodes.When subjected to external loads,the non-coordinated deformation of the metal film and the flexible substrate will cause the interface debonding and it's the main cause of damage and failure of flexible electronic devices.In order to avoid the overall failure of the flexible electronic device due to interface damage and failure,and to improve the reliability of the flexible substrate-metal film structure during service.This paper will study the interface damage behavior of flexible substrate-metal film structure from two levels of theory and numerical simulation.Theoretically,a flexible substrate-metal film structure interface stress transfer model is established,and the stress transfer mechanism between the film and the substrate is revealed;based on the cohesion theory,an analytical model of the flexible substrate-metal film structure interface that can be used for interface damage analysis is established.In terms of numerical simulation,the finite element numerical model of the flexible substrate-metal film structure is constructed through the cohesion unit,and the established numerical model is used to analyze the damage and failure behavior of the structure interface,and the factors affecting the flexible substrate-metal film structure are studied.The main work and research results of this paper are as follows:1.Based on the shear hysteresis theory,a stress transfer model of the flexible substrate-metal film structure interface considering the influence of the structure thickness is established.The established model is suitable for the initial stage of service and the interface damage under uniaxial tensile load can be negligible.The stress and strain field of the substrate,film and interface can be obtained through this model,and then the interface stress transfer mechanism can be obtained.Under uniaxial tensile load,the stress in the metal film is transferred from the flexible substrate through the interface,and the interface mainly transfers the stress in the flexible substrate to the metal film in the form of interfacial shear stress.The interface shear stress reaches its maximum value at the position of the structural load and is zero near the symmetry axis of the structure,while the normal stress in the film is zero at the position of the load application and increases to the maximum near the symmetry axis.Based on this model,the influence of structural size parameters and elastic parameters on stress transmission can be analyzed,so as to provide a theoretical analysis method for the reasonable adjustment of the thickness and elastic parameters of the film and the substrate during the preparation process of the flexible substrate-metal film structure.2.Combining the analytical method with the bilinear cohesive force model,an analytical model of the cohesive force interface of the flexible substrate-metal film structure is established.The established model has good applicability in the entire process from the elastic deformation stage to the failure of the structure interface when the flexible substrate-metal film structure is subjected to uniaxial tensile load.The model can be used to obtain the stress and strain fields of the flexible substrate,the metal film and the interface under different interface stress states.The results showed that damage and failure occurred at the edge of the interface of the flexible substrate-metal film structure first,and then expanded to the inside of the interface.This model can reveal the influence of structural size parameters,mechanical parameters and cohesion parameters on the damage evolution process of flexible substrate-metal film structure,and can provide theoretical basis for finite element numerical simulation and avoid blind selection of cohesion parameters.3.By constructing the cohesive force model unit,the finite element numerical model of the flexible substrate-metal film structure is established.This model can analyze the mechanical response of the flexible substrate-metal film structure under different service loads.The results show that for the cohesive unit at the interface,the tensile load has more influence on the interface debonding than the bending load.By comparing the calculation results obtained by the finite element model with the calculation results obtained by the theoretical model,it is found that the two are in good agreement.4.Using the finite element numerical model of the flexible substrate-metal film structure to study the factors affecting the interface damage.The results show that the material properties,structure size and cohesion parameters of the flexible substrate-metal film structure will affect the size of the damage range in the interface.Among them,the increase in the elastic modulus of the metal film and the flexible substrate will increase the range of interface damage;the increase in the ratio of the thickness of the flexible substrate to the thickness of the metal film will reduce the range of damage in the interface;the initial displacement of the interface damage increasing will reduce the range of damage in the interface;while the increase of the interface debonding failure displacement and the increase of the interface shear strength will increase the range of damage in the interface.When designing the flexible substrate-metal film structure,methods such as improving the interface bonding strength,increasing the thickness of the flexible substrate,and reducing the elastic modulus of the film and the substrate can be used to improve the reliability of the flexible substrate-metal film structure.