Effect of surface modification of multi-walled carbon nanotubes on thermal conductivity of underfill for microelectronic packaging

Abstract

In this research, multiwalled carbon nanotubes (MWCNTs) were directly functionalized with benzene-1,3,5-tricarboxylic acid (BTC) and 3,5-diaminobenzoic acid (DAB) via a Friedel-Crafts acylation with less structural damage as confirm by FT-IR, XPS and FT-Raman analysis. The functional groups on MWCNT surfaces can accelerate the curing reaction of epoxy composites remarkable inducing rather low exothermic peak temperature (T[subscript p]), exothermic heat of reaction (∆H) and activation energy (E[subscript a]). Additionally, the crosslink density (ρ) increased and free volume fraction (f[subscript g]) decreased with the addition of functionalized MWCNTs, resulting in dramatic increase of glass transition temperatures (T[subscript g]) and decrease of coefficient of thermal expansion (CTE). The thermal conductivity enhancement can be observed with functionalized MWCNT systems probably due to good dispersion and decreased interfacial thermal resistance between MWCNT and polymer matrix. Moreover, the modified Maxwell-Garnett typed EMA model is appropriate for predicting effective thermal conductivity of epoxy composites filled with low concentration of MWCNTs. Epoxy composites incorporated with hybrid fillers which consisted of MWCNTs and submicron-sized silicon nitride (Si₃N₄) exhibit higher thermal conductivity than those with single filler, thereby forming high packing density and perfectly heat conductive pathways.