Fracture mechanical test methods for interface crack evaluation of electronic packages
The experimental determination of fracture mechanical properties of interface cracks is a substantial task for the design for reliability of electronic packages. As interface cracks are dominated by a mode mix between tension and shear mode (crack driving modes I and II) a mixed mode bending method was developed to adjust the ratio of the two modes (mode mixity). For a correct extraction of an energy release rate from this kind of tests a finite element simulation has 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 at 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 displ acement 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.