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Predicting Thermal Conductivity of LTCC with Thermal vias Using an Interface Area Method
Keywords: Thermal via, LTCC, Interface method
Increased power density in microwave design for front end modules has created the need for improvement in the thermal conductivity of electronic substrates. Although LTCC has a lower thermal resistance than PCB substrates, it is still necessary to lower the resistance further by introducing thermal via arrays. The design and optimisation of vias is poorly understood and this paper addresses the theory and practice of such vias. The temperature of the filled via and LTCC interface is calculated and a method of predicting thermal performance is described using the via cylinder circumference area. From a previous study: the rule of mixtures can only indicate a trend when the fraction volume of dissimilar materials is altered. However, it does not show how via size and density influences the thermal conductivity when the percent amount stays the same. The fact that the thermal conductivity and diffusivity of the filled via is so much greater than the LTCC material means that another method of theoretically calculating the thermal conductivity can be used by studying the thermal path. The paper compares the rule of mixtures and interface area methods to the measured results. It is seen that the new method, using interface area, provides a good method of predicting the actual performance of an LTCC via array.
Tracey Vincent, Graduate Student
Worcester Polytechnic Institute
Worcester, MA

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