Preparation Of SACBN07 Solder Paste And Its Joints Resistance To Thermocycling

Lead free solder paste is an important material in Surface Mount Technology(SMT).With the rapid development of surface mount technology,the reliability of lead-free solder paste has been widely concerned.The reliability of lead-free solder paste is related to the composition of the solder,the viscosity of the solder paste,the printing effect and the reflow temperature curve.In this paper,a new type of lead-free solder paste is prepared to match the performance of SACBN07;in the printing of new type of lead-free solder paste controlling the printing parameters and setting the reflow curve for reflow soldering;with the prepared Comparison of hot and cold cycles between new solder paste and SAC305 solder paste on the market.The microstructures and mechanical properties of the interface were studied by microstructures such as shear test and nano-indentation experiment.The details and results are as follows:The results show that the viscosity of the solder paste is the best when the quality of the new solder powder is 87.5% in the experimental group by the comparison between the three groups.According to the DSC curve of SACBN07 solder,the appropriate return flow curve is developed to make the solder paste better and get reliable solder joints.The improvement of the reflow profile is the preheating zone temperature of 150 ?,the active zone temperature of 195 ?,the temperature of the insulation zone of 260 ?,the cooling zone temperature of 150 ?,and the welding time of 554 s.The spreading experiments were carried out on two kinds of solder paste SAC305 and SACBN07 under the appropriate reflow process.The spreading coefficient of SACBN07 is 84.3%,and the spreading coefficient of SAC305 solder paste is 81.1%.The spreading coefficient of the new solder paste is slightly higher than that of the SAC305 solder paste;The addition of Bi and Ni increases the spreading area of the SAC solder and improves the wettability of the solder paste.After 600 h thermal cycling,the ratio of cracked solder joint on SACBN07 / Cu is 29.2%,and the ratio of cracked solder joint on SAC305 / Cu is 48.3%,so the performance of anti-hot and cold cycle on SACBN07 solder paste is better than SAC305 solder paste.After the hot and cold cycle test,the interface layer of SAC305 / Cu interface was significantly thicker than that of SACBN07 / Cu interface after 600 h.The Bi and Ni elements in the new solder paste effectively inhibited the growth of IMC.The IMC of SACBN07 / Cu interface was worm-like(Cu,Ni)6Sn5,which was significantly fine compared with the Cu6Sn5 grain size in the interface of high silver solder paste SAC305 / Cu solder.The thickness of SACBN07 / Cu interface is 16% lower than that of SAC305 / Cu,and the growth rate of SACBN07 / Cu interface is smaller.The addition of Ni can inhibit the growth of IMC layer,The addition of Bi decreased the growth rate of IMC layer,which was lower than that of SAC305 / Cu interface IMC.After thermal cycling experiment,the hardness of SACBN07/Cu solder alloy was reduced by 17.4% compared with that before the test;the hardness of SAC305/Cu was reduced by about 31.3% compared with that before experiment,so the softening degree of SACBN07/Cu was less than SAC305/Cu.The shear strength of SAC305/Cu is 31.4% lower than that of SACBN07/Cu after thermal cycling experiment,so the shear resistance of SACBN07/Cu is better than SAC305/Cu.