Preparation And Performance Study Of Lead-free Solder Paste With High Thixotropic And Fine-pitch

With the rapid development of electronic packaging materials,the CBGA,(Ceramic Ball Grid Array Package),PBGA(Plastic Ball Grid Array Package),QFN(Quad Flat No-lead Package),0201,01005(package size)and other resistance capacity components have been widely used.However,higher requirements for surface mount technology and solder paste was put forwarded due to increased component mounting density and minute spacing between leads.Solder paste specific printing and anti-collapse has become the focus of the current reflow soldering technology development.But,our country started relatively later in this filed,especially in the fine-pitch,fine pitch and ultra fine pitch field,the solder paste used entirely rely on imports.In this paper,Sn0.3Ag0.7Cu lead-free solder paste with high thixotropic and fine-pitch was chosen as raw materials,and then the effects of film-former,active and solvent on the fine-pitch printing and weldability of solder paste were investigated.By optimizing the flux component of film-former,active,solvent and thixotropic agent and solder powder for the solder paste.The relationship and influence mechanismbetween the solder paste component and its performance were also discussed and characterized by using screen printing and reflow soldering technology and thermogravimetric analysis(TGA),viscometer,SEM,etc.The main conclusions are as follows:(1)The tetrahydrofurfuryl alcohol was selected as solvent.Also,KE-604 and Foral AX-E with 1:2 composition of the mixed rosin was used as film-forming agent,the solder paste fine-pitch printing performance is best,which can achieve 0.41mm fine-pitch pad printing.(2)The tetrahydrofurfuryl alcohol and diethylene glycol monohexyl ether were used as the solvent agent according to 1:2 proportion,KE-604 and Foral AX-E were composed of 1:2 compound rosin as the film-forming agent,and the fine-pitch pad printing spacing was reduced to 0.33mm.(3)Chosing the modified hydrogenated castor oil and BE1 combined into a complex thixotropic agent 1:2 distribution,the solvent is tetrahydrofurfuryl alcohol,film-forming agent is the KE-604 and Foral AX-E compound with rosin composed of 1:2,the resulting solder paste has excellent anti-slumping,and the fine-pitch pad printing spacing reach to 0.20mm.The slump distance of solder joint showed a trend of increase first and then decrease with the increase of thixotropic agent content,and when the thixotropic agent in a high temperature is added flux agent,the content of compound thixotropic agent was 6%,the slump distance of solder joint at the lowest level,to 0.290 mm.And the thixotropic agent in a low temperatureis is added flux agent,the slump distance of solder joint is further reduced to 0.287 mm.(4)The slump distance of solder joint decreases first and then increases with the increase of the content of the solder powder.When the solder powder content is 89.0%,the slump distance of solder joint reached minimum,with a value of 0.261mm.And the less of solder paste coating quantity,the better of the anti-slump,and the minimum slump distance of solder joint is 0.253mm.(5)Selected the main components of flux as follow:film-forming agents is KE-604 and Foral AX-E according to 1:2 composition,its quality accounts for 40%of the total mass of flux,the active agents for the azelaic acid and adipic acid with 3:1 complex,its quality accounts for 7.5%of the total mass of flux,the solvent agents is tetrahydrofurfuryl alcohol and diethylene glycol monohexyl ether by 1:1 complex,its quality accounts for 35%of the total mass of flux,the thixotropic agents is modified hydrogenated castor oil and BE1 in 1:2 combination,its quality accounts for 7%of the total mass of flux.Finally,use the selected flux and solder powder to make the solder paste at the ratio of 11:89,with high thixotropy(thixotropic coefficient Ti=0.813),cold and thermal slump resistances is perfect,and the minimum slump distance of solder joint is 0.180mm,and the bridge distance of fine-pitch pad less than or equal to 0.06mm,after reflow soldering,which can meet the fine-pitch of welding requirements.