Procedure to determine interfacial toughness of EMC-copper (oxide) interfaces

Microelectronic packages can be considered as composite structures fabricated from highly dissimilar materials. Interface delamination related failure often occurs when the packaged devices are subjected to thermo-mechanical loading. The analysis of delamination of a laminate structure with a crack along the interface is central to the characterization of interfacial toughness. Due to the mismatch in thermal mechanical properties of the materials adjacent to the interface and also possible asymmetry of loading and geometry, usually the crack propagates under mixed mode conditions. In this paper, the interface toughness of epoxy molding compound - copper interface in IC packages is characterized. The test specimen is directly obtained from a production process line. A small-size multi-functional mixed mode bending (MMB) tool was designed and fabricated. For measurements under various temperatures and moisture conditions, a special climate chamber is designed. The “current crack length” is required for the interpretation of measurement results through FEM-fracture mechanics simulations. Therefore, during testing the “current crack length” is captured using a CCD camera. The critical fracture properties are obtained by interpreting the experimental results through finite element modeling. As input parameters, the material properties are both experimentally and numerically characterized as functions of temperature and moisture. In order to get more accurate interfacial toughness, the influence of residual stresses in the sample is considered.