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Effective power dissipation and thermal management are critical in small and thin packages. In direct chip attach where flip chip and chip-on-board packages are employed, the polymer encapsulant material used is an important factor in package heat dissipation. This study deals with the development of liquid epoxy-based encapsulants with high conductivity fillers, allowing them to have enhanced thermal conductance. Two epoxy resins and a silicon-carbon liquid system, as well as aluminum nitride and boron nitride fillers,
were investigated in this study. The study revealed that packing density, which is greatly influenced by particle size and shape, is more important than the intrinsic thermal conductivity of the fillers as far as attaining high thermal conductance for liquid encapsulants is concerned. A 60 wt% load of aluminum nitride (AlN) resulted in a thermal conductivity similar to that obtained from 40 wt% load of boron nitride (BN). Without filler particle surface treatment to improve packing density and reduce viscosity, the practical loading levels for BN and AlN are 35 wt% and 55 wt%, respectively. Aluminum nitride filled resins showed higher flexural strength than boron nitride at equivalent loading levels. Both the untreated AlN and BN fillers can be used with silicon-carbon resins, with the AlN-filled system achieving a higher flexural strength and viscosity than the BN-filled system.
The study noted, however, that pretreatment of the filler particle surface is needed to reduce the viscosity of the encapsulant so that it will not incur a severe penalty in terms of rheological and mechanical properties.
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