Isotropically conductive adhesives filled with copper nanoparticles and micron-sized flakes

To meet the requirements for future fine pitch and high-performance interconnects in advanced packaging, ICAs with nano-materials are attracting more and more interest due to their specific electrical, mechanical and optical properties. There has been extensive research on nano-conductive adhesives containing nanofillers such as nanoparticles, nanowires or carbon nanotubes. In this paper, copper nanoparticles were introduced into ICAs filled with micro-sized copper flakes to study the effect of nanoparticles on the performance of ICAs. Copper particles (mainly 5~10 nm) were synthesized by reduction of copper acetate with hydrazine hydrate in the presence of cetyltrimethylammoniumbromides (CTAB) and polyvinylpyrrolidone (PVP, K-30). The nanoparticles were then surface treated with lactic acid and incorporated into epoxy matrix together with copper flakes as conductive fillers. The content of the nanoparticles varies from 3 to 30 wt.% of micro-sized particles, and the total copper filler loading in ICA is from 50 to 75 wt.%. The ICA was blade coated on glass slides and cured at proper temperatures. The effect of nanoparticles dosage on the bulk resistivity of the ICAs was studied. The microstructure of the ICAs was analyzed by SEM. The morphology studies showed that the decreased resistivity was resulted from the sintering of the copper nanoparticles.