Effect Of Trace Ag On Properties And Interface Structure Of Sn-0.7 Cu Solder

Lead-tin(Pb-Sn) solder alloys have been widely used in the modern electronics industry because their low melting points,good wettability,good corrosion resistance, good electrical conductivity and reasonable price.However,due to the toxicity of lead and its alloys,increasing environmental and health concerns and legislation restriction over the use of lead,What's more,the development of packaging technology need developing solder alloys withstanding good mechanics properties as well as electrical properties.As far now,designing new lead-free solders is a hot spot of recent researches.The effect of adding a small amount Ag on properties of the Sn-0.7Cu based alloy was studied.,and the interface microstructure between solder and Cu substrate was studied in present paper.Many kinds of their properties such as melting points,mechanics properties, overflow-ability,corrosion resistance were studied by experiments,the effect of the different composition on the properties was provided as follow:The addition of Ag can reduce melting temperature of the solders.The Ag content of solder has significantly influenced on liquidus temperature of solders.The addition of Ag can improve the overflow-ability of Sn-0.7Cu lead-free solder.When wAg=0.3%, overflow-ability of solder on the surface of Cu substrate would increase by 1.8%at 270℃. Under the condition of the Ag content are less than 0.9wt%,tensile strength of solders first increases and then decreases with the Ag content,with maximum values 32Mpa when wAg=0.6%,but the plastic property decreases with increasing of Ag content.The study found that:Brazing at 270℃,Only Cu₆Sn₅ was generated in the(Sn-0.7Cu) -xAg/Cu interface,the morphology of IMC changes with the Ag content.When the Ag content is low,the Morphology of IMCs was rough.With the increasing of Ag content, when wAg≥0.6%,the morphology of interfacial IMC became smooth.