Research On Preparation Technology Of Jet Printing Solder Paste And Solder Flux For Electronic Packaging

In order to fulfil the requirements of individual,small batch production and 3D packaging technology with a further reduction of solder joints spacing,the solder paste jet printing technology has been developed.However,the mature jet printing solder paste products are foreign products up to now.For the sake of achieving the domestication of jet printing solder paste,this paper studies the comprehensive performance of the self-developed flux system,and the flux of the optimized formula was used to mix with SAC105 NO.5 fine powder to make the solder paste.The anti-collapse property,jet printing performance,microstructure and hardnessof these formulas were tested and analyzed for the purpose of improved performances.The results showed that the acceptable solderability and spreading ability of SAC105/Cu joints can be achieved by using the as-designed solder flux with 4wt.% of weak organic acid activator composed of glycolic acid and phthalic acid with a proportional ratio of 1:1,and the solder flux prepared by the activator can avoid the failure of ion transfer due to ionic migration under humid condition,and has strong electronic stability on PCB.A series solder flux with the concentration of ST-modified hydrogenated castor oil(ST-HCO)as the single thixotropic agent with the content of 4wt.%-10 wt.% was designed.The corresponding test results showed that the A6 solder flux composed of 9wt.% ST-HCO,50 wt.% film-forming agent,4wt.% activtor,30 wt.% solvent and 7wt.% other additives has the highest thixortopy index of A series solder flux,featuring with 30.2Pa·s,0.51 and 7.62% of the viscosity(?),thixotropic index(TI)and non-recovery rate(R),respectively.B series solder flux with ST-HCO and polyamide wax 6650(PA-6650)as the composite thixotropic agent,consisting of 7wt.%-5.5wt.% and 2wt.%-3.5wt.%,respectively was designed.The corresponding test results showed that the B4 solder flux composed of 5.5wt.% ST-HCO,3.5wt.% PA-6650,50 wt.% film-forming agent,4wt.% activtor,30 wt.% solvent and 7wt.% other additives has the highest thixotropy index of B series solder flux,featuring with 75.3Pa·s,0.77 and 0.27% of the viscosity(?),thixotropic index(TI)and non-recovery rate(R),respectively.C series solder flux with 125 hydrogenated rosin as film-forming agent with a content of 42-50 wt.% was designed.The corresponding test results showed that the C3 solder flux composed of 5.5wt.% ST-HCO,3.5wt.% PA-6650,44 wt.% film-forming agent,4wt.% activtor,36 wt.% solvent and 7wt.% other additives has the highest thixotropy index of C series solder flux,featuring with 36.2Pa·s,0.81 and 6.63% of the viscosity(?),thixotropic index(TI)and non-recovery rate(R),respectively.A6,B4 and C3 solder fluxes were chosen to mix with SAC105 NO.5 fine powder for the preparation of jet printing solder pastes.By performing the collapse tests under room and high temperatures,all three solder pastes were found to meet the requirement of JIS-Z-3284 standard.Through jet printing tests,C3 solder paste whose thixotropic index is the highest found to have the best continuous jet printing performance with a smooth accomplishment of 60×40 array jet print.Microstructure observation showed that C3 solder paste welded joint had compact structure and no voids.The thickness of intermetallic compound layer was about 4 microns.The results of nanoindentation test showed that the hardness of C3 solder paste is 190.51 MPa.