Evaluation on interfacial strength of polyimide film/si substrate structure by nanoindentation method

Nanoindentation tests were conducted for polyimide (PI) coating/Si substrate specimens and the energy release rates were evaluated as the interfacial strength. The energy release rate due to a coating delamination was obtained from the load-displacement curve by the method proposed by Omiya et al. The correcting method was proposed for the case that the energy dissipation due to the viscosity of materials occurs. Three specimens that have different thickness were prepared. The dependencies on the coating thickness and delamination propagation rate were investigated. The interfacial strength of the thinnest coating case is underestimated, since small scale yielding conditions were not satisfied. The value of the interfacial strength between PI coating and Si substrate increases with increasing of the delamination propagation rate. The value becomes constant when the delamination propagation rate exceeds around 7.0 × 10-3mm/s. On the other hand, the critical strain intensity factor is constant irrespective of the delamination propagation rate. This result suggests that the opening displacement at the delamination edge is constant for the range of the propagation rate investigated.