High thermal conductivity and temperature probing of copper nanowire/upconversion nanoparticles/epoxy composite

Epoxy resin has been intensively used as an electronic packaging material for its good mechanical strength and electrical insulativity. However, the low thermal conductivity of epoxy resin limits its applications. Inorganic fillers with a high loading fraction (>30 vol%) is typically used to enhance the thermal conductivity. But the high loading fraction could degrade the mechanical property and challenge the processing. In this work, we develop a new class of epoxy composites comprising very long (up to tens of micrometers) single-crystalline copper nanowires (a diameter of ∼20 nm and a length of up to ∼40 μm) as filler. A high thermal conductivity of 2.59 W/mK was obtained at a very low loading fraction of Cu nanowires at 0.12 vol%, corresponding to an 8-fold enhancement in thermal conductivity of plain epoxy resins. We also demonstrate that ytterbium and erbium codoped sodium yttrium tetra-fluoride (NaYF4:Yb/Er) upconversion nanoparticles can be concomitantly incorporated into the epoxy composite, providing an accurate temperature of the composite. The dual functionality should render the epoxy composite an attractive candidate in electronic device.