Abstract
An epoxy-thiol system filled with boron nitride (BN), in the form of 80 µm agglomerates, has been investigated with a view to achieving enhanced thermal conductivity. The effect of BN content on the cure reaction kinetics has been studied by differential scanning calorimetry (DSC) and the thermal conductivity of the cured samples has been measured by the transient hot bridge method. The heat of reaction and the glass transition temperature of the fully cured samples are both independent of the BN content, but the cure reaction kinetics is not: with increasing BN content, the reaction first advances and is then delayed, this behaviour being more pronounced than for the same system with 6 µm BN particles, investigated previously. This dependence on BN content is attributed to the effects of heat transfer, and the DSC results can be correlated with the thermal conductivity of the cured systems, which is found to increase with both BN content and BN particle size. For a given BN content, the values of thermal conductivity obtained are significantly higher than many others reported in the literature, and achieve a value of over 4.0 W/mK for a BN content of about 40 vol %.
Highlights
The design of modern microelectronic systems involves increasing miniaturisation and operation at higher frequencies than hitherto, resulting in increased power densities, and greater risk of failure as a consequence of heat management problems
2 of 18in comparison with about 0.2 W/mK for conventional printed circuit board technology. Both higher and lower values of thermal conductivity than that presented by the above Both higher and lower values of thermal conductivity than that presented by the above commercial commercial systems have been reported in the literature for epoxy-boron nitride (BN) and epoxy-aluminium nitride (AlN) composites; systems have been reported in the literature for epoxy-BN and epoxy-AlN composites; we provide we provide here a brief review of the results obtained for epoxy-BN composites, this being the system here a brief review of the results obtained for epoxy-BN composites, this being the system investigated investigated in the present work
The cure kinetics of epoxy-BN composites, in which the epoxy is cured with a thiol, has been studied by differential scanning calorimetry (DSC), and has been found to be correlated with the thermal conductivity of the cured composites
Summary
The design of modern microelectronic systems involves increasing miniaturisation and operation at higher frequencies than hitherto, resulting in increased power densities, and greater risk of failure as a consequence of heat management problems. It has been estimated that the failure rate of an electronic device doubles with every 10 ◦ C increase in chip junction temperature [1], while for light emitting diodes (LEDs), there is a rule of thumb that every increase in operating temperature of 10% reduces the service life by 50% [2] Thermal dissipation from such devices is clearly of great importance. The usual design involves the use of insulated metal substrates (IMS), in which the printed circuit layer (the heat source) is bonded to a metal substrate (the heat sink) by means of a dielectric layer, the properties of this layer being of prime importance in defining the performance of the IMS. The two principal properties required are electrical insulation and high thermal conductivity, which should be combined with ease of processing (the dielectric layer is usually the adhesive between the printed circuit layer and the metal substrate) and affordable cost
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