| Electrically Conductive adhesives(ECAs)are functional adhesives with both adhesion and conductivity,which mostly applied in the form of paste dispensing or film coating.ECAs with film form can be machine shaped by die cutting or laser cutting,and the uniformity and viscosity of the film are easy to achieve a thickness uniformity and low overflow of the adhesive layer.These features would lead to many advantages in performance and processing technology,such as more precise relolution,simple process and easy large-scale application,for example,conductive bonding for PCB board and metal plate,radar antenna array,heat sink and RF module.In this paper,the preparation mechanism and method related to the resin matrix of the conductive adhesive film are analyzed.The effects of resin components,additives and conductive silver powder on the properties of conductive adhesives are studied.On this basis,two kinds of isotropic conductive adhesive films with different properties were prepared,which can meet the requirements for the structural bonding with high strength and the flexibility bonding with low stress.The curing behavior and process adaptability of the high strength ECA film was studied.At last,nanomaterials was introduced to the conductive adhesive film to improve the electrical conductivity.The bisphenol A epoxy based matrix for the conductive adhesive film with film-forming properties and adhesive wettability was prepared by the chain extension,elastomer toughening and other methods.The effects of toughening agents,curing agents,various additives and functional additives on the film formation,mechanical performance,conductivity and other properties of the conductive adhesive film were studied with the rheological analysis,the four-probe resistance test and other methods,and the preparation process of the conductive adhesive films was established.The effects of micron silver powders with different morphologies and content on the shear strength and volume resistivity of the conductive adhesive films were discussed.The Raman spectroscopy and SEM analytical methods were adopted to study the mechanism of improving conductivity by a surface treatment of micron silver powder with glutaric acid.The high-adhesion conductive adhesive film is based on the epoxy resin with 30%toughening agent and 7?m flake silver powder as the conductive filler.The shear strength can reach more than 17MPa,the glass transition temperature is 118?and the volume resistivity is less than 2.9×10-4?·cm.The high-adhesion conductive film is suitable for high-strength conductive bonding.It has good resistances to the environmental tests such as thermal cycling,moisture and salt spray test,the bonding performance retention rate is more than 85%,and the conductivity has no significant change,which means it has a good durability and a reliability.The research on the curing process shows that the adhesive film has a good processing adaptability,and can be fully cured within 1 hour at 120?150°C.The low-stress conductive adhesive film is prepared by adjusting the amount of elastomer and the ratio of macromolecular resin.It has a lower glass transition temperature,and can show flexibility after curing.The shear strength can reach 6MPa,the 90°peel strength is 16.8N/cm,and the volume resistivity is less than 3.5×10-4?·cm.It is suitable for bonding large areas and various surfaces with very different expansion coefficients.The conductive properties of the adhesive film are improved with the nano silver wires and graphene.The research finds that the nanomaterials can enhance the connection between the conductive particles,increase the number of conductive paths,reduce the percolation threshold and improve the conductivity of the adhesive film.The silver nanowires with a diameter of 50nm and a length of 150?m can decrease the volume resistivity of the adhesive film by 58%when the addition amount is 6%.When the addition amount of graphene is 0.06%,the volume resistivity of the adhesive film is reduced by 52%. |
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