Direct Thermal Path Pcb

- Jan 03, 2017 -

Abstract 

Discrete power sources, such as light emitting diodes (LEDs), are often mounted on a metal core printed circuit board (MCPCB) in an effort to manage the heat output of these power sources.  The metal core, typically aluminum or copper, dissipates heat from the power sources by functioning as a heat spreader. With the increasing heat fluxes from LEDs, a metal core with a higher thermal conductivity will be required to cool future heat fluxes.  This paper will introduce a replacement for the MCPCB that utilizes the superior thermal spreading of 500 W/mK natural graphite in conjunction with a unique assembly design using standard FR4 printed circuit boards or flex-circuits.  The MCPCB replacement has a ~ 22% reduction in weight when compared to the aluminum MCPCB.  The natural graphite solution was shown to reduce the overall thermal resistance by ~ 1.7°C/W, mitigate “hot-spots” and improve temperature uniformity. Both experimental measurements and numerical models were used to analyze the aluminum and natural graphite configurations. 

Introduction 

The continuing increase in electronics power density, specifically in discrete heat generating electronic components such as LEDs, ASICs, CPUs, GPUs and solid state relays, has required the industry to redesign circuit boards for optimum thermal performance.  Today, the metal core printed circuit board provides improved thermal performance over standard FR4 circuit boards, even with thermal vias [1].  The MCPCB commonly consists of a metal core layer (typically aluminum or copper), a continuous dielectric layer and a copper circuit layer.  The metal core provides a means for heat spreading as a result of its high thermal conductivity.  The increase in the LED junction temperature has been known to have many detrimental effects including the reduction in lifetime, reliability and lumen output [2].  

One emerging material in many consumer electronic applications is natural graphite.  Natural graphite, with its light weight, formability and high in-plane conductivity of 500+ W/mK, has emerged as a superior heat spreading solution in many consumer electronic applications including cell phones, laptops and plasma display panels (PDPs)[3], [4].  In this work, experiments were performed to compare the thermal performance of a LED mounted on a commercially-available MCPCB compared to a natural graphite replacement. 

Board Configurations and Setup 

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