Design of Anisotropic Thermal Conductivity in Multilayer Printed Circuit Boards

The design of anisotropic thermal conductivity in multilayer printed circuit boards (PCB) is studied, where the flow of heat is manipulated through the informed layout of circuit board electrothermal traces. Three representative circuit board configurations are considered to illustrate the basic method. A baseline circuit board (Configuration 1) comprising a heat-generating device in thermal communication with a heat sensitive device by the way of a standard electrical trace connection is studied first to characterize heat flow due to conduction and convection. Building off of this baseline structure, the thermal management advantages and disadvantages of a closed heat shield for anisotropic PCB thermal conductivity are explored using the second circuit board (Configuration 2). The design of the third multilayer circuit board (Configuration 3) with optimized anisotropic PCB thermal conductivity for enhanced heat flow control is simultaneously explored. It is experimentally shown that, for PCBs subject to free convection and power densities on the order of 1-10 W/cm
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, the design technique allows for noticeable (-10 °C) reduction in the temperature of the heat sensitive device without a significant (<;3 °C) increase in the heat-generating device temperature. The experimental heat transfer results are verified through simulations that further confirm and explain the functionality and limitations of the heat flow control concept. The effect of Joule heating is also investigated numerically. A conceptual framework for electrothermal codesign of multilayer PCBs with integrated heat flow control and more device-dense packaging is proposed.