A mathematical model for predicting heat generation caused by the chemical reaction of epoxy compounds used for encapsulation of semiconductor devices has been developed. First, a model to describe isothermal heat flow changes was derived as a function of time and temperature. On the basis of this model, procedures to describe heat generation under actual non-isothermal conditions were developed. Two kinds of commercial molding compounds were used in this study. Parameters in the model were determined by isothermal DSC (Differential Scanning Calorimetry) runs. The calculated heat flow profiles fit well with experimental data for both isothermal conditions and for a heating rate of 5K/min. For a heating rate of 20K/min, the peaks of the calculated values of both materials were higher than those for the experimental data. The discrepancy was caused by the model neglecting the phenomenon of total heat saturation at a defined temperature T_L corresponding to the glass-transition temperature T_g. After accounting for the T_L, calculated profiles fit well with the experimental data under all conditions.

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The reciprocating plastication process in injection molding is a dynamic phenomenon during which the relative positions of the screw and the heating cylinder change cyclically. In our previous report, we proposed a visualization analysis method for this process using a glass-inserted heating cylinder. In this study, based on the above proposed method, we carried out an analysis of the reciprocating plastication process using polyethyleneterephthalate, polyamide, polystyrene and polycarbonate. The results are summarized below:
(1) The characteristic plastication processes of the above-mentioned resins in the screw channel could be explained by an extended lamination image of the screw channel and the solid-bed ratio calculated from the image. We were also able to explain the phenomenon of the formation and disappearance of a void (pellet-unfilled area) in the screw channel of the feed zone during the early stages of the charging process for each resin.
(2) The void formed during the initial stages of charging because of a melt-plugging phenomenon occurring in some parts of the screw channel in the feed zone, due to the melting of the resin during the waiting time. This phenomenon resulted in an insufficient supply of resin in the nozzle side of the melt-plugged area, hence forming a void. Moments later, pellets with a wider volumetric space located on the hopper side and compressed by the continued screw rotation would push the melt-plugged area to the nozzle side, causing the void to disappear.

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The sandwich injection molding technique can be adopted in a wide range of engineering applications. In this study, plate samples with holes were molded by using the sandwich injection molding technique, and the effects of the injection velocity of the core material and the viscosity ratio of the skin/core materials on the weld line generated in the region just behind the hole were examined. The results clearly showed that the lower viscosity and the higher injection velocity of the core material result in the thicker core layer, and that the depth of the V-notch of the weld line decreased with this. This suggests that generation of the weld lines in sandwich injection moldings, which is due to combination of two flow fronts of the skin material, is also affected by the flow behavior of the core material.

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