Silica Fillers Embedded in Epoxy Molding Compound Cause Inner Stress Concentration

This paper investigates the influence of silica fillers on the tensile mechanical properties of epoxy molding compound (EMC) by uniaxial tensile testing at room temperature. We adopted two kinds of EMC dog-bone shaped specimens containing silica fillers with 0 wt% <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathbf{EMC}^{\mathbf{0}\mathbf{wt}\%})$</tex> and 65 wt% <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathbf{EMC}^{\mathbf{65}\mathbf{wt}\%})$</tex>. The stress-strain <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\boldsymbol{S}-\boldsymbol{S})$</tex> curves showed that <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{EMC}^{\mathbf{0}\mathbf{wt}\%}$</tex> is ductile and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{EMC}^{\mathbf{65}\mathbf{wt}\%}$</tex> is brittle. Notably, the Young's modulus of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{EMC}^{\mathbf{0}\mathbf{wt}\%}$</tex> ‘ is smaller than that of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{EMC}^{\mathbf{65}\mathbf{wt}\%}$</tex>, but the tensile strength of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{EMC}^{\mathbf{0}\mathbf{wt}\%}$</tex> ‘ was about 25 % higher than that of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{EMC}^{\mathbf{65}\mathbf{wt}\%}$</tex> ‘. This fracture behavior was caused by the local stress concentration around the silica fillers as suggested by the finite element analysis. The scanning electron microscopy observation of the fracture surfaces also supported this view.