Research On The Way To Improve The Solderability Of SnAgCu Solder And Reliability Of Soldered Joints

By means of wetting balance method and spreadability method, the wetting time , wetting force and the wetting angles of Sn3.0Ag0.5Cu lead-free solder were tested under the conditions of different temperatures and coatings on substrates. The results indicate that with the increase of test temperature the wettability of Sn3.0Ag0.5Cu lead-free solder on substrates improves remarkably, the solder possesses best wettability at 260℃and the wettability of Sn3.0Ag0.5Cu solder on Ni/Au coating substrate is better than that of the solder on OSP coating substrate.PCB and simulative specimens soldered with layer resistances were cleaned by SMT water-cleaning system. The results indicate that after being cleaned by water cleaning solution, the concentration of residue on PCB surface with layer resistances mounted by Sn3.0Ag0.5Cu solder paste meets the requirement of correlative standards but cleaning parameters, such as cleaning time, have great effect on cleaning results.Experiments on reliability of SnAgCu/Cu and SnAgCu/Au/Ni/Cu soldered joints was carried out under the condition of high temperature storage and the shear strength of SnAgCu/Cu and SnAgCu/Au/Ni/Cu soldered joints was tested, macrostructures of fracture were observed by optical microscope, microstructures of fracture were observed by scanning electronic microscope (SEM) and fracture mechanism was also analyzed with regard to the specimens experimented by way of high temperature storage. The results show that the shear strength of SnAgCu/Cu soldered joints and SnAgCu/Au/Ni/Cu joints decrease with the increase of the time of high temperature storage, but all the experimental data meet the requirement of correlative standards, so SnAgCu/Cu and SnAgCu/Au/Ni/Cu soldered joints are considered reliable under the condition of the experimental paramerers. The shear strength of SnAgCu/Cu soldered joints is larger than that of SnAgCu/Au/Ni/Cu joints, the shear strength of SnAgCu/Cu soldered joints is affected by high...