This paper describes studies of heat transfer in a rapid thermal processing-type oven used for several semiconductor wafer processes. These processes include 1) rapid thermal annealing, 2) thermal gradient zone melting, and 3) lateral epitaxial growth over oxide. The heat transfer studies include the measurement of convective heat transfer in a similar apparatus, and the development of a numerical model that incorporates radiative and convective heat transfer. Thermal stresses that are induced in silicon wafers are calculated and compared to the yield stress of silicon at the appropriate temperature and strain rate. Some methods of improving the temperature uniformity and reducing thermal stresses in the wafers are discussed.
A h i t e Werence analysis has been developed which predicts the temperature, pressure, and velocity distributions for the flow of thermoplastic materials in straight and tapered, hot and cold walled circular flow channels. This analysis when combined with the cavity Elling analysis described in Part 11, gives the molding engineer the capability of modeling the injection molding process from the shot to the cavity during injection. The information that is obtained from these analyses is useful in equipment design and modification since it allows numerical experiments to be performed so that one ma ascertain the effects on moldability of flow channel a n 8 cavity geometry, material properties, and operating conditions. In addition, the information is useful in problem diagnosis and analysis to ascertain causes of and evaluate potential solutions to moIding problems.
A practically-oriented computer model which computes the temperature, pressure, andvelocity fields in a cavity during the mold filling portion of the injection molding process is described. The model is structured so that it can be used for cavities having non-simple shapes and for commonly used molding compounds with complicated viscosity, shear rate, temperature relationships. Predictions from the model are found 'to be in good agreement with results obtained from exact solutions to special cases. Model predictions in molding problems have been found to correctly describe trends such as an increase in the pressure required to fill molds as injection rate, shot temperature, and mold temperature decrease, and to be reasonably accurate when compared to data for plaque, disc, and telephone housing molds over a wide range of molding conditions. Some illustrative examples of the use of the model in solving real molding problems are provided.
In response to increasing ecological and economic pressures, a two‐shot molding process has been developed to recycle molding plastics. This process buries scrap plastic under a skin of virgin plastic in the molded part, resulting in a laminate that has the appearance of and similar mechanical properties to the skin material only. Two injection units and a special nozzle design are used to achieve the desired lamination. Theoretical and experimental studies have been conducted to determine the effects of parameters on the amount of scrap material that can be buried and its effect on impact strength. With conventional production molding dies, scrap plastic comprising approximately 40 percent of the total shot has been molded beneath virgin plastic in parts having stringent appearance requirements.
Considerable effort has been expended recently by a number of researchers to develop methods of simulating the flow of polymers in injection molding dies. The computer models developed by these researchers provide the mold designer with useful quantitative information concerning the predicted effect of design parameters on mold, filling characteristics. This paper will describe some recent work which is aimed at increasing the usefulness of these models by more accurately describing the flow behavior of those polymers, such as polycarbonate resins, which exhibit a strong effect of pressure on viscosity.
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