Investigation of Fracture Toughness and Displacement Fields of Copper/Polymer Interface Using Image Correlation Technique

摘要

Delamination between the copper leadframe and the epoxy molding compound of microelectronic devices is a common failure concern. Interfacial adhesion characterizes the resistance of an interface to initiation and growth of interfacial delamination. In general, interface strength is an important factor for the successful fulfillment of package requirements such as structural integrity in micro- and nanoelectronic applications.rnIn conventional delamination testing methods, the critical force which leads to crack initiation or propagation together with the actual crack length are needed. Displacement fields can be used for the exact measurement of crack tip at the moment of crack onset or as it advances. A testing method which has been set up for a high resolution analysis of delamination process is further developed to investigate the displacement fields at the crack tip of polymer/metal interface. Bilayer metal/polymer specimens were employed to measure the adhesion strength in terms of interfacial fracture toughness using Four-Point Bending (4PB) and End Notched Flexure (ENF) delamination tests. During the bending tests, high resolution images of the crack tip area were taken at different loading stages. These images were analyzed later using the microDAC technique (i.e., micro deformation analysis by image correlation). The microDAC approach is based on the application of digital cross correlation on grey scale submatrices of the analyzed images. The result is a full-field displacement description of the analyzed surface. This allows for the in-situ measurement of the crack length during the delamination test. In addition, the effects of mode angle and elevated temperatures on the interfacial fracture toughness were investigated in this work.