The Effect of Cu Content on Performance of SnAgCuNiBi /Cu Soldering

In recent years, SnAgCu (SAC) lead-free solder is widely used to substitute for SnPb solder. However, there are still two issues to be solved urgently.One is that the price of mainstream SAC solder is much more higher because of higher Ag content in the solder.The other is that high-Ag lead-free solder appears more brittle and is susceptible to impact and vibration. It is difficult to meet the requirement of electronic product, especially in the field of mobile devices. So it is necessary to develop a low-Ag lead-free solder with low cost,excellent solderability and improved strenth.

In this paper, A new low-Ag lead-free SAC solder is shown.The effect of Cu content on the solderability and joint performance are investigated. Interface IMC layer morphology and fracture mechanism of joint are analyzedd by SEM, Deep-etched and shear strength test. It is revealed that higher shear strength of joint appears only Cu element content is about 0.5% in solder. Polyhedron IMC grains appears in the interface only Cu element content is about 0.5% in solder after aging. As Cu content increases in the bulk solde, the IMC grain size and number increase. On the other hand, the interface IMC layer is thinner and IMC grain size is bigger, which is the reason that the shear strength of solder joint decrease when adding excess Cu element in the solder.