Multiplexing frequency mode study of packaging epoxy molding compounds using dynamic mechanical analysis

Dynamic mechanical analysis (DMA) measures mechanical properties (modulus and damping) of viscoelastic materials over a spectrum of time (or frequency) and temperature. This paper reports its use to study four epoxy molding compounds (EMC1A, 1B, 2 and 3) for electronic packaging industry using multiplexing frequency (or multiple frequency) mode DMA. The raw epoxy molding compounds were processed under 1 min transfer mold curing (TMC) but different post-mold curing (PMC) conditions. Viscoelastic properties over temperature at fixed oscillatory frequency of the compounds were studied. Specimen EMC1B with longer PMC (4 h) resulted in higher glass transition temperature (Tg) compared to EMC1A (0 h PMC) of the same brand of material. The other two brands of epoxy molding compounds EMC2 and EMC3 behave differently from EMC1 as shown from their Tg variations. It was observed that Tg’s of all compounds studied were generally increasing with higher oscillatory frequency DMA temperature sweep. Activation energies (Ea) at Tg relaxation process of compounds were calculated from Arrhenius plots, log f versus 1/Tg. Effects of different curing conditions of compounds on Ea were also discussed. It was noticed that EMC1B after 4 h PMC resulted in Ea of about 3.4 times higher than EMC1A (0 h PMC). Application of time–temperature superposition (TTS) technique to the multiplexing frequency mode analysis of the cured epoxy molding compounds was illustrated. Master curves, of modulus as a function of oscillatory frequency of the compounds, were therefore constructed and generated at temperature interval of 20° of each compound. Performance of specimens at specific operating conditions can be predicted and compared.