| The performance of microelectronic devices is sensitive to temperature. When a diode assembly is electrically powered, heat is generated and the temperature in the assembly rises. In a TVS diode assembly composed of silicon, nickel, solder and copper, the solder controls the extent of temperature rise since it is the material with the lowest thermal conductivity. Hence, it is essential to know the minimum value of thermal conductivity in the solder that delivers acceptable performance and reliability. A finite element program was used to calculate thermal transients in a diode assembly with a fixed current of 60 A. It was found that if the thermal conductivity of the solder layer falls below 12.7 W/m-K, the assembly will not operate reliably.; Voids in the solder will reduce the effective thermal conductivity of this layer. A model was used to relate the effective thermal conductivity of the solder layer to the void fraction and thus evaluate the maximum void fraction that allows reliable operation and acceptable diode performance. It was found that the solder layer should not contain more than 33% spherical voids. |
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