Fabrication And Properties Of A New Type Of Low Silver Lead-free Solder Paste SACBN07

With a ban on lead publishing globally,Scholars from all countries are committed to finding a product which could replace Sn-Pb solder paste.SAC305 was widely used in lead-free electronic assembly process.But high silver content in SAC305 increased costs of solder.In recent years,our laboratory developed a new type low silver lead-free solder,Sn-07Ag-05Cu+Bi Ni(SACBN07).Three kinds of solder paste were fabricated by mixing three different kinds of flux(A?B? C)with the same solder powder SACBN07.This work focuses on the performance of SACBN07 solder pastes.The results show that:1.The stability,p H,density,and corrosion of three kinds of flux were investigated.The C flux was less stable under low temperature conditions,and the B flux was more corrosive in three fluxes.Through the metallography and scanning experiments,large lacuna was found in solder point of B solder paste.The mixing ratios of solder and flux(A,B,C)were determined according to printing performance of different kinds of flux.The mass fraction of the solder powder were 88.5 %,87.5 %,87.5 %,respectively.2.The condition of solder paste printing process and reflow soldering process were optimized,and print gap of solder paste was adjusted.The height of solder joints was quiet small with none print gap.And the phenomenon of inconsistent of joints size was found with print gap.To ensure the consistency of joints size,the pad-joined method was designed after several experiments.A suitable reflow profile of SACBN07 was set up through adjustment of soldering time and reflow soldering oven temperature of each zone.3.The wettability of solder pastes with different solder and different flux was investigated,respectively.With the same solder SACBN07,the spreading coefficients of B solder paste was 88.1 %,better than that of A solder paste was 84.3 %,and also better than the spreading coefficient of C was 79.3 %.With the same flux,the spreading coefficients of SACBN07,SAC305 and SAC0307 are 84.3 %,84.1 % and 73.3 % respectively.The Bi and Ni promoted in wetting and improved the wettability of low-content silver solder paste.4.After 165 ?,200 h aging experiment showed that the flux had little effect on the growth of IMC on the interface after reflowing.Bi and Ni elements decreased the diffusion rate between Cu and Sn,which result in the thickness of IMC layer of SACBN07 lower than that of SAC305 and SAC0307 after aging.And in a certain aging time,little Cu3 Sn compound was found between the IMC layer on the interface and the Cu pad.5.The addition of Ni in SACBN07 solder paste could refine grains,and the addition of Bi can increase the hardness of the solder joints improving the mechanical properties.Result in the shear properties of SACBN07 solder paste with the low content of silver are better than that of SAC305 and SAC0307.