Preparation And Mechanism Of Nano-silver Conductive Composites

With the development of electronic packaging, electrically conductive adhesives (ECAs), one of the interconnecting materials, have experienced huge application and advancement. ECAs with high conductivity own great potential market share. Metal nanoparticles sinter at a temperature much lower than the melting point of its bulk material. And metal nanoparticles are able to be applied for much finer pitch interconnection. With the above advantages, metal nanoparticles have been the focus of research and applied in the electronic packaging industry. Research on the low temperature sintering of silver nanoparticles and surface treatment of silver fillers were conducted in this paper in order to improve the conductivity of ECAs.The sintering behavior of silver nanoparticles was observed by SEM. Different kinds of reagents were applied to surface functionalize silver nanoparticles. Surface functionalized silver nanoparticles were filled into the ECAs. ECAs filled with propanedioic acid, pentanedioic acid and hexanedioic acid treated silver nanoparticles showed lower resistivity. The adsorption of pentanedioic acid on silver nanoparticles was studied by DSC and Raman spectroscopy. Pentanedioic acid replaced the original organic layer on silver nanoparticles and desorbed from 150℃. TGA curve showed that the amount of pentanedioic acid adsorbed on silver nanoparticles was 1.67wt%. ECAs with silver nanoparticles as part of conductive fillers, had higher resistivity than those with micro-sized silver flakes.The conductivity of electrically conductive adhesives (ECAs) was improved by surface functionalizing silver flakes with dicarboxylic acids, or by directly adding dicarboxylic acids into ECA. The resistivity of ECAs was among 2-5×10-5Ω·cm. Raman spectroscopy and X-ray photoelectron spectroscopy revealed that the pentanedioic acid was chemically adsorbed onto the silver flake surface with monodentate bond. The differential scanning calorimetry (DSC) results indicated that pentanedioic acid promoted the curing reaction of epoxy in both processes, and thus increased conductivity of ECAs.Printed electronics have become research focus due to their distinct characteristics such as tiny, flexible, thin, and easy to carry. Printed electronics have shown great potential in daily use, such as RFID tags, smart cards and displays. Silver nanoparticles have been applied as conductors in printed electronics. Different kinds of chemicals were used as solvent and stabilizers to prepare silver ink in the paper. Silver inks were annealed at certain temperature to thermally decompose the stabilizers and solvent. The resultant nano silver films were sintered and highly conductive. The resistivity of conductive silver films prepared by using lactic acid and ethylene glycol was 2.6×10-5Ω·cm and 6.4×10-6Ω·m after annealing at 200℃and 250℃for 30min, respectively. The microstructures of conductive lines formed by this method were investigated by SEM and SPM.It is possible to prepare highly conductive ECAs that are cured at a lower temperature if silver nanoparticles with smaller dimension were used as conductive fillers. Future work can also pay attention to the choice of reagents and resins in the formula of ECAs to make full use of the low temperature sintering and high line resolution of silver nanoparticles.