Plastic deformation and failure modes of moulding compounds during indentation loading and their importance for the quantitative characterisation of adhesion

Different test methods are used within the microelectronics community to quantify adhesion of material combinations interacting inside the package. Button Shear Tests or Bending Tests are popular test methods for studying moulding compound adhesion on various surfaces. The measured data obtained from these tests is a superposition of the characteristics of the interface, the experimental setup, and the test vehicle's geometry and materials used. Compressive contact, for example, between shear or bending tool and the sample might lead to plastic deformation. Nanoindentation on bulk moulding compound strips showed that plastic deformation under compressive loading does occur. Low indentation forces lead to a levelling of the rough surface. For higher forces residual imprints after indentation can be as deep as 15 μm. Test vehicles are very often only a few millimetres in size. Thus, sub-micron accuracy for displacement measurements becomes a necessity when extracting energies from force-displacement curves. Plastic deformation at the shear contact then needs to be subtracted from measurement data in order to achieve accurate adhesion results.