An energy-based method to predict delamination in electronic packaging

The propensity and significance of interfacial delamination as a crucial failure mechanism in electronic packaging have been well documented in many papers. Many of the failure criteria were used to solve 2-dimensional problem with a pre-crack. However, in real electronic packages, the size and location of the cracks or/and delamination cannot be predicted. It is not easy to use the traditional fracture criteria to deal with more complicated 3-D delamination problems. The potential delamination interface of copper leadframe/Epoxy Molding Compound (EMC) was selected in the study. The stresses of the interface were evaluated by the Button Shear Test. A series of Button Shear Tests was conducted to evaluate the adhesion properties of Epoxy Molding Compounds (EMCs) on copper substrate. In each of the tests, the critical load acting on the EMC of the button shear sample was measured at different shear angles and a finite element model was used to evaluate the stresses at the interface between the mold compound and the copper substrate. In this paper, an energy-based method is proposed by deriving the energy to initiate each of the tensile and shear modes of failure across the interfaces of the button shear test samples for the chosen EMC/leadframe material system. Component stresses were extracted from the numerical simulation in order to compute the distortional strain energy density, (U_d), and the hydrostatic strain energy density, (U_h), relating respectively to the shear and tensile mode. (U_d) and (U_h) were calculated from the Young´s modulus of EMC and the average stresses within a selected region of the finite element model where it exhibits high stress values.