Dynamic constitutive relation of EMC over a broad range of temperatures and strain rates
In this paper, dynamic properties of EMC were studied sat different temperatures and different strain rates. Firstly EMC was investigated by quasi-static tests. Secondly a series of dynamic compressive experiments of EMC were conducted using the Split Hopkinson Pressure Bar (SHPB) at high strain rates. Corresponding measurements were conducted at temperatures ranging from 20°C to 200°C. The results indicate that the yield strength and flow stress of EMC increase remarkably with the increase of strain rate. However, the yield strength of EMC is almost unchanged with the increase of temperature which is ranging from 20°C to 200°C.
EMC characterization and process study for electronics packaging
Transfer molding process has been used in the packaging industry for decades for the encapsulation of all kinds of plastic packages. In the transfer-molding process, the solid but reactive epoxy molding compounds (EMCs) in the preformed pellet form are injected into the preheated mold that contains the substrate and the attached chip. The EMCs are thermally cured and then ejected with encapsulated parts. For microelectronics encapsulation, EMC selection and molding conditions can strongly affect the final quality of the encapsulated parts, such as warpage, wire sweep, microvoid formation and reliabilities. In this study, the curing behavior of two epoxy molding compounds from different sources was evaluated. The activation energies for curing reactions were estimated using Kissinger and Ozawa methods. These two EMCs were also subjected to process study through transfer molding. The warpage values of the encapsulated substrates with a dummy die were measured and the molded parts were inspected using an acoustic microscope. The processing conditions of these two EMCs were optimized. The determining factors for warpage control and void formation were evaluated through the design of experiments.
Studies of effect of dynamic preloads on mechanical properties of steel
In order to determine the effect of load history upon the yield characteristics of a low-carbon steel, specimens of low-carbon steel have been subjected to initial dynamic compressive or tensile loads. The load-time function was approximately that of a sine wave of half-period duration with a half-period time of about 1 msec. The intensity of the load was varied; scme specimens were subjected to elastic strains for loads in excess of the static yield stress but less than the dynamic yield stress, while in others gross yield was initiated. These specimens were then aged for a short time at temperatures ranging from 68 to 250°F and then retested dynamically or in static tension. Upper and lower yield stresses and the inelastic microstrain which preceded gross yield on the retest have been used to evaluate the extent of damage and recovery. The results of these studies tend to confirm a yield phenomenon predicted by dislocation theory.