Nanoindentation loading rate sensitivity of the mechanical behavior of cured isotropic conductive adhesives

The mechanical properties of isotropic conductive adhesive (ICA) have received increasing attention due to its widespread application in microelectronic packaging. In this work, the loading and strain rate sensitivity of cured epoxy-based ICA were investigated using nanoindentation. The ICA was prepared and indented under quasi-static and continuous stiffness measurement (CSM) modes under varying loading rates (\(\dot{P}\)) and loading strain rates (\(\dot{P} / P\)). The results demonstrate a loading/strain rate hardening effect on the hardness of ICA. Compared with quasi-static test measurement, the CSM mode seems to be a more effective measurement for the hardness results of ICA. During nanoindentation, a competitive interaction between hardening and softening mechanisms was observed: softening dominated at higher loading strain rates, while hardening prevailed at lower rates. Under both loading modes, creep displacement and creep strain rate increased with strain/loading rate. In addition, the creep displacement rose rapidly during the initial holding time before stabilizing, while the corresponding creep strain rate decreased progressively to a steady-state creep stage.