A Study On The Mechanical Behavior Of The Initiation And Propagation Of Cu-PDMS Interconnect Interface Delamination In Flexible Electronic Packaging

With the rapid development of microelectronics industry and semiconductor field,flexible electronic devices have been widely used in biomedical,smart phone and other fields.Compared with traditional rigid plastic encapsulated microcircuits,the complex deformation of flexible electronic devices in the process of production and service will lead to the interface delamination failure.In view of the common layered failure problem of flexible electronic devices,the paper conducts reliability analysis on the heterogeneous interface between Cu thin film and PDMS substrate during packaging.Firstly,it qualitatively analyzes the reliability problems of typical interconnect structures in production.Secondly,it studies the crack initiation and propagation behavior of the film-substrate interface by combining experiments with the finite element analysis,and explores a method for testing the interface strength so as to obtain a set of cohesive zone model parameters that could characterize the interface properties.Finally,it uses the parameters to quantitatively predict the initiation and propagation of interface delamination in the actual service process.The main results are as follows:(1)The reliability analysis of interconnect structure interface is conducted by the shared node method.Firstly,the feasibility of the method is demonstrated from the grid division method,grid density and condition setting.Secondly,the interface stress distribution and failure modes of different interconnect structures are analyzed.The failure modes of horseshoe,U-shaped and linear interconnect structures are all interface slip failures caused by the increase of local strain in the tensile process,and the failure mode of the serrated interconnect structure is the tearing failure caused by normal warping of the serrated tip.Finally,the influence of geometric shape and material parameters on the reliability of interconnect structure is discussed with the local strain variable as the index.(2)A set of cohesion parameters that can characterize the initiation and propagation of Cu-PDMS interface delamination is obtained by combining experiments with the simulation method.Firstly,an experimental loading device suitable for DMA Q800 loading block and constraint guide plate is designed,and the manufacturing method of experimental samples with prefabricated cracks is introduced in detail.Secondly,the force-displacement curve causing the crack of Cu-PDMS interface is obtained by tensile test.Finally,based on the experimental data,the critical energy release rate is obtained by theoretical calculation,and the ultimate tensile strength is obtained by the indirect inversion method,and the separation characteristics are described,and the simulation results are in good agreement with the experimental results.(3)Based on the bilinear cohesion model,the interface delamination initiation and propagation at the interface of linear interconnect structures are predicted and characterized.In the bending mode,the maximum normal displacement of crack initiation at the interface end is found to be about 2.2mm in the simulation analysis without prefabricated crack.It is found in the simulation results containing prefabricated cracks that,with the increase of bending displacement,the interface crack propagates simultaneously at the interface end and at the two ends of the prefabricated crack,and the farther the prefabricated crack is from the end,the faster the prefabricated crack propagates under the same displacement.In the tensile mode,it is found that the local transverse tensile rate of crack initiation at the interface end is about 15% in the simulation analysis without prefabricated crack.When the prefabricated crack is located between the interfaces,the interface delamination always begins on one side of the prefabricated crack.When the prefabricated crack is located on the Cu surface,with the movement of the prefabricated crack position to the end,the propagation length of the interface layer on both sides of the crack shows a decreasing trend.In this work,the research method can quantitatively predict the initiation and propagation of the interface delamination in the film-substrate of flexible electronic devices.The research results provide a basis and reference for further research on the reliability of the interface of flexible electronic devices.