Design And Performance Study Of New No-clean Flux And Solder Paste

With the rapid development of the electronic information industry,surface mount technology(SMT)has gradually become the main assembly technology.As the most critical material in SMT technology,solder paste has gradually developed into a low-silver lead-free series to reduce environmental pollution.Solder paste is mainly composed of flux and solder powder mixed in a certain proportion.In order to reduce the waste of resources and labor,the new no-clean flux gradually replaces the traditional water cleaning and solvent cleaning flux to occupy the main development trend.The nature of the solder paste affects the performance of the entire electronic assembly.Therefore,it is important to study the no-clean low-silver solder paste.This paper mainly studies the determination of the flux composition of the solder paste and the related performance test of the flux,the selection of the solder powder,the preparation of the solder paste and the performance test of the solder paste.The mass ratio of the solvent was determined by orthogonal test:isopropanol:diethylene glycol:glycerol:ethylene glycol butyl ether is 3:5:8:1,accounting for 70 wt.%of the total mass of the flux.The active agent was selected from lactic acid:glutaric acid is 3:2;the ratio of the compounded acid to triethanolamine was 7:3,and the total mass fraction was 13 wt.%.Film former was hydrogenated rosin:polymerized rosin=1:1,10 wt.%;thixotropic agent was activated hydrogenated castor oil,4 wt.%;corrosion inhibitor was benzotriazole,0.5%;antioxidant was OP-10,0.5 wt.%;stabilizer was paraffin,1 wt.%.The performance of the formulated flux was investigated and compared with two commercial fluxes.The self-made flux was light yellow viscous liquid with good stability,no precipitation and stratification,and the pH is 5.8.The self-made flux had good wettability;the expansion rate of the solder joint reaches was 80.5%,and the contact angle was 23°.It was less corrosive to the copper substrate,no penetrating corrosion,no patina and corrosion spots.The non-volatile content was 32.5%,halogen-free,and overall performance was good.The prepared flux was stirred and mixed with SAC0307(Sn99Ag0.3Cu0.7)solder powder having a particle size of 25-45 ?m in a ratio of mass ratio of 10.5:89.5 to obtain a solder paste.Compared with two commercial solder paste,the viscosity of the self-made solder paste was 116 Pa·s,the thixotropy coefficient was 0.59,the coefficient of non-recovery was 0.52;there was no collapse under cold and hot conditions,no bridging.The tensile strength was 12.7MPa,the shear strength was 20.11MPa,which was ductile fracture.The evaluation grade of the paste tin bead was one grade.After heating for 6 min according to the reflow soldering curve,a continuous dense intermetallic compound layer was formed at the joint of the solder joint and the substrate,the thickness was 6.57 ?m.When a circular hole with a diameter of 0.8 mm was used as a template,the spread area of the solder joint was 1.21 mm2.