The Effect Of RE Content On Creep And Aging Properties Of Low Ag Content SnAgCu Solder Joints

With the rapid development of Surface Mount of Technology (SMT) and lead-free solder alloy, the reliability of lead-free solder joints has become one of the focusesin the fields of micro-joint. SnAgCu system solder alloy is considered as one of themost potential succedaneums. The creep and aging properties of reliability of lead-freesolder joints has become the focuses. But science nowadays, it is rarely reported thereliability of low Ag content SnAgCuRE solder joints, so it is becoming the very keyproblem in the SMT practical application in the recent years. It has extraordinarysignificance to investigate lead-free solder and corresponding to improve the quality ofelectronic products by carrying out relative work.In this paper the low Ag content SnAgCu solder alloy is melted under the vacuumconditions, the commerial used Sn3.8Ag0.7Cu solder alloy is as the reference frame.The best RE adding content can be found from the effects of adding tiny rare earth inthe Sn2.5Ag0.7Cu lead-free solder alloy on creep properties, and it is also investigatedthat the effect of environment conditions on creep properties. The growing dynamicsof intermetallic compound (IMC) of solder joints interface region and the effect oftemperature on the thickness of IMC are analyzed in the oil mediator aging processbased on the shear strength of Sn2.5Ag0.7Cu and Sn2.5Ag0.7Cu0.1RE solder joints.The RE adsorption property and the effect of the thickness of intermatllic compound ofinterface region on the shear strength are also discussed in the creep and aging process.The creep test results show that adding tiny rare earth (RE) in the low Ag contentSn2.5Ag0.7Cu solder alloy is just changing the size and shape of IMC of solder jointsinterface region to improve the reliability. When the RE adding content ofSn2.5Ag0.7Cu solder alloy is 0.1wt%, the creep rupture life of solder joints is longest(5760min.), which is more highly than that of Sn2.5Ag0.7Cu solder alloy (804min.)and is obviously higher than that of commercial used Sn3.8Ag0.7Cu solder alloy (1116min.), the initiation place of crack of Sn2.5Ag0.7Cu0.1 RE is in the center sectionof solder alloy and the crack character is mainly intergranular crack with little"mountain peak" transcrystalline fracture. But the crack origin is in the intermatlliccompound of interface region and the fracture pattern is intergranular crack ofSn2.5Ag0.TCu solder alloy. When the RE adding content of Sn2.5Ag0.7Cu is 0.5wt%,there would be petal-like RE compound in the solder alloy, which can prevent thesolder alloy wetting properties and forming the soldering flaw, so the fracture patternis intergranular crack.The interface region Cu₆Sn₅ thickness of solder joints is considered as one of themost importance factors of reliability, the reliability can be improved by adding tinyrare earth, which can inhabit the growing of Cu₆Sn₅. The aging test results show thatthe shear strength of solder joints is decreasing with increasing of aging time andheightening aging temperature. The dynamics curve of IMC(Cu₆Sn₅,Cu₃Sn) thicknessis coincidence with the law of parabola-growth in the aging process of Sn2.5Ag0.7Cuand Sn2.5Ag0.7Cu0.1RE solder joints, the constant of Cu6Sn5 and Cu3Sn growing rateof Sn2.5Ag0.7Cu0.1RE decrease to 79.3% and 82.8% of that of Sn2.5Ag0.7Cu solderjoints, in other words, the reliability can be improved by adding tiny rare earth toprevent the IMC growing. When the general intermatllic compound in the interfaceregion is over the 4μm, the shear strength of solder joints is sharply decreased, and thefracture pattern is changing from the typical transcrystalline crack to transcrystallineand intergranular crack with the aging time increasing and aging temperature rising.So considering comprehensively Sn2.5Ag0.7Cu0.1RE solder alloy has goodproperties and has better foreground for applying.