Preparation Of Micro-silver Powder And Application In Conductive Silver Pastes

Silver is the most common metal raw material in the electronics industry.Due to the low resistivity,environmental protection,and stable physical and chemical properties,the conductive silver paste prepared by silver particles is widely used in solar cells,membrane switches,conductive adhesives and other fields.Micron-sized flake silver powder is considered as an ideal silver paste conductive filler.In the same quality,the flake silver powders have a high volume conductivity,not only improving the conductivity of silver paste,but also reducing production costs.Among the important performance indicators of conductive silver pastes,there are many studies on the effect of silver powder on the conductivity of silver paste,but few reports on the particle size of flake silver powder influencing the flexibility of silver paste,and few of those silver paste can keep both excellent electrical conductivity and flexibility.In this paper,Micron-sized flake silver powders with different particle sizes were successfully prepared by liquid phase chemical reduction method and ball milling method.The effect of reduction and ball milling parameters on the morphology and particle size of silver powder products was studied.In addition,flake silver powders with different particle sizes were used as conductive fillers to prepare conductive silver pastes with excellent conductivity and flexibility simultaneously.The influence of particle sizes on the resistivity and flexibility of silver paste was investigated.The main conclusions of this paper are as follows:(1)Micron-sized flake silver powders and spherical silver powders were successfully prepared by the one-step liquid-phase chemical reduction method using citric acid and succinic acid as dispersants respectively.The particle size of silver powders can be controlled by changing the dispersant concentration.The particle size of flake silver powders are 1?2?m.With the increase of citric acid concentration,the particle size of silver flakes increases,and the edge morphology changes from smooth to rough.The particle size of spherical silver powders are 3?8?m.With increasing the concentration of succinic acid,the particle size of the silver powder increases and the agglomeration phenomenon is reduced.It shows that the type and concentration of dispersant can control the morphology and particle size of silver powder,and the mechanism of controlling the growth of silver powder has been explored.(2)Micron-sized flake silver powders were successfully prepared by high-energy ball milling method using 1?3?m silver particles as raw material.The effects of ball milling parameters on the morphology and particle size of silver powders were investigated.It was found that the longer the ball milling time was used,the better the flake-forming property and the larger the particle size of the silver powder were obtained.The ball milling efficiency and the flake-forming property of the silver powders were also affected by the ball milling speed,the ball-to-material ratio and the concentration of the ball milling medium.When the ball-to-material ratio is 10:1,the ball milling speed is 250 r·min^-1,the ball milling time is 24 h,and adding 3 ml anhydrous ethanol,the silver powders prepared by ball milling have less agglomeration and better flake-forming property.The particle size of the silver powder are 2?6?m.(3)Different kinds of low-temperature solidified conductive silver pastes were prepared by mixing different micron-sized flake silver powders.10?m,5?m,and 3?m,and 200 nm nano-silver powders were using as conductive fillers.The resistivity and the resistance folding change rate were tested to characterize the electrical conductivity and flexibility of the silver paste.The results show that using the silver with large particle size,the better electrical conductivity and the worse folding resistance are obtained.As the particle size becomes smaller,the electrical conductivity of the silver paste decreases,and the folding resistance increases.Therefore,in the experiment,10?m silver powder with the best conductivity and 5?m silver powder with the best bending resistance were mixed in different proportions to prepare conductive silver paste,maintaining the original excellent conductivity and improving the flexibility of the silver paste.The influence mechanism of the particle size of silver powders on the properties of silver pastes were explored.It is proved that small silver flakes can fill the pores of the large silver flakes,which increasing the contact area between the silver powders.After folding,the small silver flakes can complement in the crash to maintain conductivity aisle.In addition,the nano-silver powder is added to the mixed silver powder,and the performance of the silver paste is further improved.When the proportions of four types of silver powder are 60%,20%,10%,and 10%,a specific resistance of the silver paste is 2.27×10^-6?·m and the resistance change rate is 23.5%.