Authors: J. Keller, I. Maus, H. Pape, B. Wunderle, B. Michel
Affilation: AMIC Angewandte Micro-Messtechnik GmbH, Germany
Pages: 155 - 158
Keywords: mode mixity, interface cracks, fracture mechanics, electronic packaging, mixed mode bending, gray scale correlation, deformation measurement, crack tip detection
The ongoing development of highly integrated electronic packages leads to a steadily increasing number of material interfaces within a package. In combination with increasing harshness (vibration, humidity, temperature) of the system environment the reliability of such packages is often dominated by interface fracture. Therefore interface fracture mechanics is one of the main focuses of electronics reliability research. The determination of fracture mechanical properties of interface cracks is a substantial task for the design for reliability. Without experimental determined fracture mechanical parameters such as the critical energy release rate a reliability forecast based on simulation results cannot be given. As interface cracks are dominated by a mode mix between tension and shear mode (crack driving modes I and II) a method was developed to adjust the ratio of the two modes (mode mixity), Fig. 1. The so-called mixed-mode bending method is based on the work of Xiao . For a correct extraction of an energy release rate from this kind of test a finite element simulation have to be carried out. As the crack driving force is not independent from the crack length, correct crack tip detection has to be guaranteed during the test. The authors present a combined simulative and experimental method for crack tip location determination of interface specimens. The specimens are loaded in the testing apparatus and images of the crack tip at the interface are taken at different load states during the testing procedure. Then images are analyzed by image correlation techniques and the displacement fields are determined. In the next analysis step the displacement fields are compared to fields from finite-element analysis of the same specimen geometry with similar boundary conditions as the experimental setup. The point of the best matching of the experimental and simulative field is the actual crack tip location. If finite-element data or analytical solution for the crack tip displacement field is available the method can be applied for a variety of different interface samples.
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