Synthesis and characterization of silica-silver core-shell structural spheres and its application in conductive adhesive

摘要

In recent years, the core-shell hybrid materials are one of the hotspots in current research and attracted widely attentions[1]. The hybrid particles have good conductivity, while the density and cost would be greatly reduced as compared with the pure silver powder. And the hybrid particles have applied in the electromagnetic shielding materials, conductive coatings and absorbing materials because of its unique structure and physical and chemical properties. As a substitute for tin-lead solder, the conductive adhesive had some defects, such as high cost, high volume resistivity and thermal expansion coefficient (CTE) [2]. The silicon oxide had extremely low thermal expansion coefficient (CTE) and low price and the nano-silver particles had low temperature sinterability. So the SiO_2@Ag hybrid materials applied in conductive adhesive may obviously reduce the thermal expansion coefficient (CTE) and cost, while maintaining a low volume resistivity. However, most of hybrid materials synthesis processes involved complicated procedure and equipment or expensive reagents and poor stability. [3, 4] So, herein, SiO_2@Ag hybrid particles with uniform, dense coverage and thickness controllable silver layers were successfully prepared by a simple and environmentally friendly approach without surface modification of SiO_2. The effects of activation process, reaction solution concentration and size and type of silicon oxide on the growth of silver nanoparticles were studied emphatically. At the same time, the hybrid particles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Energy Dispersive X-ray microanalysis (EDS) and UV-Vis absorption spectroscopy. The results show that the crystallinity of silver layer was good and the morphology of silver nanoparticles on the surface of SiO_2 could be tailored with changing in the type of silicon. If sintering the hybrid particles at 200°C for 30min and the silver nanoparticles on the surface of SiO_2 became larger obviously. Comparing with the traditional conductive adhesive which usually has the CTE1/CTE2 at 120ppm and 220ppm, here using the SiO_2@Ag hybrid particles as filler, the CTE1/CTE2 could be greatly reduced to 25ppm and 45ppm meanwhile still keep the good conductivity of 5.0×10~(-5)Ω·cm.