A reduced percolation threshold of hybrid fillers of ball-milled exfoliated graphite nanoplatelets and AgNWs for enhanced thermal interface materials in high power electronics

Thermal interface materials (TIMs) are essential components to deplete the accumulated heat with efficient thermal management in the majority of power electronic systems such that the interfacial thermal resistance (ITR) should be significantly reduced. A reduced percolation threshold of hybrid fillers of ball-milled exfoliated graphite nanoplatelets and AgNWs are used for enhanced thermal interface materials via the assembly of high-quality ball-milled exfoliated graphite nanoplatelets (BMEGN) and AgNWs on a flexible Polydimethylsiloxane (PDMS) substrate. BMEGN modified surface with increased specific area and reduced percolation interface, together with the generation of effective 3D thermal conductive pathways between the 2D graphite and 1D AgNWs, which was experimentally measured to possess the significant improvement in thermal conductivity. The proposed method of thermally conductive film of AgNWs at the loading of 2.0 mg/mL can dramatically increase the in-plane thermal conductivity (K_//) to 29.2 W/mK, while the through-plane thermal conductivity (K_┴) shows the value of 4.94 W/mK by using the reduced percolation threshold. Anisotropy reaches up to K_///K_┴ = 5.9 with the proposed percolation, which is much larger than filler only BMEGN, indicating that the effective thermal conductive path (TCP) can be networked on a PDMS polymeric to thermally dissipate high power electronics with enhanced heat management capability. Both CPU and IGBT tests of the proposed TIMs with fillers of AgNWs loading 2.0 mg/mL can effectively minimize temperature rise to ~16 °C and ~17 °C as favorably compared with thermal grease alone. Furthermore, transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used for surface morphology, microstructure evolution, disorder evaluation, phase analysis and thermal stability of the composite material.