Effect Of Trace Rare Earth Sm On Sn-Cu-Ni Solder And Joint Intermetallic Compounds

Network and information economy is one of the most rapidly developing industry fields in the world, which is based on the microelectronics industry. Connection is a key technology in the manufacturing of electronic products, which not only can guarantee the design performance of the chip, but also is a bottleneck restricting the production efficiency and reliability of electronic products. Reliable connection needs excellent solder, and because of the low cost, as well as the physical and mechanical properties can meet the requirements of a variety of soldering methods, Sn-Cu series lead-free solder has become one of the largest amount of lead-free solder varieties in use.In this paper, Sn-0.7Cu-0.05Ni-XSm solder was the research object, by adding different mass(0, 0.25, 0.05, 0.1, 0.2 wt %) of rare earth samarium(Sm), to study the melting point, wettability properties of Sn-0.7Cu-0.05Ni-XSm solder and the interface microstructure and shear properties of joints formed by the solder and the bare copper PCB substrate, and then carry out aging experiments for 24 h, 96 h, 360 h at 160 ?.The melting point of Sm was measured by DSC, and the results show that the melting point of Sn-0.7Cu-0.05 Ni can be reduced by proper amount of Sm, and when the content of Sm is 0.05 % the melting point is the lowest, which is 226.81 ?.The effect of Sm on the wettability was studied by measuring the spreading area on copper sheet with Auto CAD. The results show that the proper amount of Sm can improve solder wettability, and when the Sm content is 0.1 %, the wettability is the best.The solder's microstructure was observed and analysed with scanning electron microscope(SEM). The results show that in the process of forming solder joints the addition of Sm can improve the interfacial morphology and inhibit the growth of interfacial compounds(IMC), but it can not change the chemical composition of the interfacial compounds, which is still(Cu,Ni)6Sn5.It was found that the interfacial compounds' morphology was changed from the initial scallop shape to become flat and uniform since the longitudinal growth and relatively fast lateral growth, and the thickness was increased by the time; In aging Sm can inhibit the growth of interfacial compounds, and when Sm content is 0.025 %, the inhibition effect is best, but with the increase of the content, it will still play an inhibitory effect, but the effect is weakened, until no effect.Carry out shear test with different Sm content solder joints, and the results show that the amount of Sm can improve the shear strength. When the Sm content is 0.025 %, the shear strength is the maximum, and it is decreased with the increase of Sm content. After aging for 360 hours at 160 ?, when the Sm content is in the range of 0.025 %~0.05 %, the shear strength of solder joints is higher than the solder joints without Sm.