| The conductive adhesive has better printing performance than the solder paste,which can meet the requirements of higher precision.Jet printing technology solves the problem of control of solder paste’s height in screen printing and it is also suitable for soft substrate printing,which may possible make it have wide application in complex integrated circuit.However,jet printing technology has not been developed completely and it is time to explore a kind of conductive adhesive which is suitable for jet printing and fast curing at the same time.The effects of different components of conductive adhesives on printing and curing performance are studied in this paper.Different analysis methods are used to test viscosity,volume resistivity,phase transformation temperature and so on.The influences of opening time,printing temperature,curing agent and content of silver powder on printing are studied.Besides,curing time,curing temperature,curing agent and content of silver powder are studied in curing performance.The opening time has little effect on the shape and diameter of the printing point.However,the weight of the printing point decreases first and then increases with the increase of opening time.Besides,there are sharp and irregular shapes in the printing points when the temperature is below 55℃.The curing process has influence on the electrical and mechanical properties of the conductive adhesive after curing.When the curing temperature is lower than the temperature of the crosslinking reaction,the curing process is not complete,and the resistivity shows large.The shear strength of the conductive adhesive increases with the increase of curing time.The conductive adhesive can be cured completely when the curing temperature reaches the temperature of crosslinking reaction and the resistivity decreases with the increase of the curing temperature.The shear strength increases with the increase of curing time in the initial stage of curing process and the conductivity and shear strength begin to decrease when the curing time reaches a certain range.Curing temperature over 140℃ can be difficult to get good conductivity and shear strength.Compared with the conductive adhesive containing triethanolamine which can be printed well,the conductive adhesives containing methyl hexahydrophthalic anhydride and dicyandiamide are difficult to be printed.According to the results of viscosity test,when the shear rate is low,the viscosity-shear rate curves of conductive adhesives which contain triethanolamine and dicyandiamide are similar,which means that they have the similar rheological properties.However,the viscosity of conductive adhesive which contains methyl hexahydrophthalic anhydride is higher.It is found that the volume resistivity of conductive adhesives with different curing agents continue to decrease with the increase of curing time.The high volume resistivity shows that the conductivity of conductive adhesive which contains methyl hexahydrophthalic anhydride is weak and the shear strength is lower than conductive adhesives which contain triethanolamine and dicyandiamide.It is also found that when the curing time is more than 20 minutes,the shear strength of conductive adhesives which contain triethanolamine and dicyandiamide is stabilized at about 11MPa.The nozzle can be blocked when the content of silver powder rise to 50vol%while it has great printing performance when the content is 40vol%and 30vol%.Although the conductive adhesive with 30vol%silver powder has strong shear strength,the weak conductivity limits its application. |
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