Study On Preparation And Curing Properties Of Copper-based Conductive Paste

With the updating and iteration of intelligent electronic products,miniaturization,high integration and three-dimensional packaging have become the general trend of the electronic packaging industry.It plays a key role for conductive paste in the assembly and packaging of various chips and components.However,it is expensive and prone to electromigration phenomenon for traditional conductive silver paste,which can destroy the reliability of packaged components.Copper powder is cheap and has high conductivity,so it is particularly necessary to study a new copper-based conductive paste with better curing properties,which meets the need of jet printing technology and can be used for multi-dimensional packaging.In this paper,copper powder was used as the conductive phase,and the low-melting alloy Sn-3Ag-0.5Cu powder was used as the reinforced phase.The effects of curing temperature,time and the content,morphology and particle size of the copper powder and the reinforced phase on the properties of the copper-based conductive paste were studied systematically with a combined method including viscosity test,conductive performance test,shear strength test and other test.The mechanism of the low melting point alloy powder as the reinforced phase were explored as well.In addition,combined with the jet printing technology,the influences of jet printing parameters such as rammer pressure,paste pressure,nozzle temperature,the content and morphology of metal powder on the jet printing performance of conductive copper paste were also investigated.It was found that the increase in curing temperature and time is conductive for the low melting point alloy powder to wet the copper powder particles and form a good bond on the surface of the copper powder,fully connect the copper powder particles which have not formed contact.It can optimize the internal conductive path of the copper-based conductive paste and improve overall properties.However,the initial decomposition temperature of epoxy resin,the binder of copper-based conductive paste,is about 250?to 280?.A large amount of epoxy resin will be decomposed,and some organic carriers will be evaporated,which will result in many pores and cracks to destroy the internal conductive path if the curing temperature continues to increase.What is worse,stress concentration phenomenon is likely to occur,which will worsen the bonding strength.All things considered,a suitable curing process for the copper-based conductive paste prepared in this paper is to cure at 250?for 20 minutes in N₂atmosphere.It can enhance the conductivity and binding strength to add appropriate low melting point alloy powder to conductive copper paste.Adding low melting point alloy powder too much will reduce the proportion of copper powder,which is not conducive to comprehensive performance,so the reasonable quality ratio of copper powder to alloy powder is 3:1.There is a seepage threshold in the influence of the content of total metal powder on the paste.After reaching this value,continue to increase the content of the metal powder,the electrical conductivity will no longer be significantly improved.On the contrary,it will deteriorate the mechanical properties of the paste after curing.There is a certain relationship between the printing performance of the copper-based conductive paste and the jet printing parameters such as the rammer pressure and the nozzle temperature.But the paste pressure of paste has little effect on it.As the pressure of the striker increases,the greater the positive pressure received when the paste is sprayed,the greater the impact force when the dots reach on the substrate surface.The temperature of the nozzle will change the viscosity and surface tension of the paste during printing.At the same time,the content of copper powder and low melting point alloy powder and the shape of the copper powder will also affect the viscosity of the paste.If the viscosity of the paste is too large,the fluidity is low,it will easily lead to more sharpening and bridging of the printing dots.If the viscosity is too small,the printing dots will easily collapse and the dot diameter will increase,which will affect the printing accuracy.In this paper,the P1 component copper-based conductive paste exhibits the best printing performance at a rammer pressure of 450 k Pa and a nozzle temperature of 50?.