Study On Microstructure And Properties Of SnCuNiGaNd Solder

Sn-Cu lead-free solder has been widely used in wave soldering because of its good soldering performance and low cost.Sn-Cu-Ni solder as the improved product of Sn-Cu lead-free solder has more outstanding advantages.It not only improves the fluidity and wettability of solder,but also reduces the"bridging"phenomenon of solder joints.With the circuit structure of electronic products becoming sophisticated,the performance requirements of lead-free solder become much more stringent.So it is urgent to develop a new type of high reliability lead-free solder.Under this background,this paper further improves the structure and properties of Sn-Cu-Ni lead-free solder by adding rare elements Ga and Nd in order to improve a new type of lead-free solder with and high reliability and market competitiveness.Take the differential scanning calorimetry and wetting balance method to investigate the melting characteristics and wettability of Sn-0.7Cu-0.05Ni-0.5Ga-xNd lead-free solder.It was found that the melting point of Sn-0.7Cu-0.05Ni solder decreased slightly from 228.2?to 226.3?,and the melting range decreased greatly from about 7?to about 3?.And the wettability of solder is significantly improved When the content of Nd element is 0.05wt%.When the test temperature reaches 260?,the wettability time of Sn-0.7Cu-0.05Ni-0.5Ga-0.05Nd solder is<1s,which meets the application standard of wave soldering.It is found that the microstructure of solder matrix and solder joint is obviously refined after adding proper amount of rare earth Nd element(0.05 wt.%).The precipitation phase size is smaller and distributed uniformly in granular form.It can be found that the precipitated phase of SnCuNiGa-xNd/Cu joint is Sn-Cu-Ni-Ga-Nd phase,and the proportion of Nd element in Sn-Cu-Ni-Ga-Nd phase increases with the increase of Nd element content;the interface layer of solder joint is composed of Cu₆Sn₅ and a small amount of(Cu,Ni)₆Sn₅,and the thickness of the interface layer is obviously reduced.When the content of Nd element is 0.05wt%,the mechanical properties of SnCuNiGa-xNd/Cu solder joints can be significantly improved.The shear strength of Sn-0.7Cu-0.05Ni-0.5Ga-0.05Nd solder joint is 46N,about 27.8%higher than that of the solder joint without Nd element.It is found that with the increase of aging time,the number of precipitates and the thickness of intermetallic compound layer increase.When the addition of Nd element is 0.025-0.05wt%,the precipitates in the interface structure of solder joints are small in size,and the intermetallic compound layer is thin and even in morphology.The shear strength of solder joints decreased with the increase of aging time,and the shear strength of Sn-0.7Cu-0.05Ni-0.5Ga-0.025Nd solder joints decreased the lowest after aging for 720h.