| Conductive adhesive is a kind of functional adhesive made by combining conductive filler with polymer matrix.The polymer matrix can provide excellent mechanical properties and viscosity,and the conductive filler with different surface morphology and particle size can achieve the electrical and thermal conductivity of the adhesive.Compared with lead-tin welding,conductive adhesive has the advantages of high efficiency,low forming temperature,green environmental protection,low cost,weather resistance,acid and alkali corrosion resistance.Conductive adhesives are widely used in chip packaging,electromagnetic shielding protection,liquid crystal conductive connection and other fields.In this project,two kinds of vinyl silicone oil are used as the basic polymer of silicone conductive adhesive,an one-component addition silicone conductive adhesive with high performance,low cost and suitable for industrial application was prepared by adjusting the ratio and filling amount of flake silver and spherical silver conductive fillers.The preparation of conductive adhesive is mainly carried out from the following two aspects in this paper:（1）Formulation design and optimization.When the flake silver:spherical silver=1:1.6 and the filling amount is 740 phr,the conductive filler can effectively lap together to form an excellent conductive network and significantly improve the electrical conductivity of the adhesive.The filling of organic modified fumed silica R974 can significantly improve the mechanical properties of the conductive adhesive and endow the conductive adhesive with excellent thixotropic properties,so that the prepared conductive adhesive has the characteristics of low viscosity and high strength.The addition of silane coupling agent KH560 containing epoxy group can significantly enhance the interfacial adhesion.The final optimized formula is as follows:HG-1:HG-2=4:6,conductive filler 740phr,fumed silica（R974）12 phr,silane coupling agent（KH560）12 phr.The volume resistivity of the prepared conductive adhesive is 1.29×10-4Ω·cm,the tensile shear strength is 1.11 MPa,and has suitable viscosity.The crystallization temperature and glass transition temperature are-77.78℃and-124.54℃respectively,and the thermal decomposition temperature is 350℃,which can meet the basic needs of conductive adhesive in chip packaging.（2）Optimize the process conditions and application evaluation.Based on the effect of diluent on the system,we adjusted the curing conditions of the system,and studied the effects of vacuum defoaming temperature and time,curing temperature and time on the properties of conductive adhesive.The changes of properties of conductive adhesive before and after storage were tested.Finally,the dispensing effect of conductive adhesive was evaluated under different dispensing parameters.The conclusions are as follows:defoaming 60 min at 40℃in vacuum can effectively remove solvents,reduce the pores formed by solvent volatilization and improve adhesion,and better properties can be obtained by curing 90 min than under other conditions,with volume resistivity of 1.46×10-4Ω·cm and tensile shear strength of 1.33 MPa.Moreover,the conductive adhesive still has good practicability after being stored for 30 days.Fine dispensing can be achieved by using needles with 0.26mm inner diameter.When the pressure is 0.4 MPa,the glue output rate is about 50 mg/min,the glue point is uniform,and there is no drawing and lodging phenomenon. |
