Browsing by Subject "Solder and soldering--Mathematical models"

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A numerical study of the thermal processes relevant to infrared solder reflow
(1990) Bhandari, Ravi Kumar, 1947-; Bergman, T. L.
A numerical model has been developed to predict the transient thermal response of a card assembly subjected to heating conditions found in the infrared solder reflow process. Predictions are compared to analytical solutions and experimental results to validate the model. Additional simulations give insight to important transport mechanisms and suggest the level of sophistication needed to model the infrared solder reflow process. A PCB populated with an array of nine modules is simulated with radiative heating supplied from above and below. The center module's thermal response and the temperature differences across the board and leads are reported. The card assembly geometry is varied to investigate the effects of shading. These simulations are repeated with the use of two simple radiative analyses, which assume minimum and maximum shading effects, respectively. The detailed radiative analysis predictions exhibited the important effects of shading. As shading is increased by increasing the modules' heights, the increased module surface area counteracts the decreased module-to-panel heater view factor and the module's thermal response and temperature differences across the board and leads are relatively unchanged. As shading is increased by decreasing the intermodule spacing, a slower module thermal response causes a greater temperature difference across the board and leads. In contrast, these thermal characteristics were not shown in the predictions of the simple analysis models
An experimental study of the thermal processes relevant to infrared solder reflow
(1990) Fernandes, Neil Joseph, 1967-; Bergman, T. L.
An experimental system has been built to replicate, as closely as possible, the radiative and convective conditions during the infrared solder reflow process. Experiments were performed to measure the transient thermal response of modules for different module array configurations, under combined radiative and convective conditions. Numerical predictions have been obtained to i) identify and quantify the heat transfer mechanisms responsible for the transient thermal response of a center module within different array configurations and ii) to determine the level of modeling sophistication necessary to develop a detailed numerical model that can predict the thermal response of the card assembly. A comparison of the center module's thermal response in a uniform height array and in an array with different module heights illustrates the the module's sensitivity to shading. The predictions and measurements show the general need to incorporate the radiative exchange analysis which includes module-to-module radiative interactions and detailed evaluation of view factors. The predicted heat transfer mechanisms associated with the center module's thermal response shows that, for the case considered here, radiation is the dominant mode of heat transfer and is influenced by i) shading of the module's sides from the infrared panel heaters and ii) radiative exchange with neighboring modules. The convective cooling rate, although smaller than the radiative heating rates for the results presented here, increases with Reynolds number due to increasing convection coefficients. Radiative and conductive heat transfer rates through the gap separating the module and the card are small