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Over the glass transition temperature, epoxy molding compound strongly exhibits viscoelastic behavior which causes its Young's modulus to be not only temperature-dependent but also time-dependent. In the present study, the viscoelastic properties of epoxy molding compound such as Prony coefficients, relaxation time and time-temperature shift factors are used for the delamination analysis. At the same time, end-notched flexure tests have been conducted at high temperatures under different loading rates for the investigation of the effect of viscoelasticity on the interface delamination between epoxy molding compound and copper. It is found that the energy release rate can still be a criterion for the viscoelastic bimaterial interface crack problem during lead-free solder reflow process. Furthermore, the critical energy release rate is rate-dependent and usually the critical energy release rate increases with the increase of loading rate for the interface delamination between epoxy molding compound and copper.