Study On The Microalloying And Interface Microstructure Of Sn-0.7Cu Lead-Free Solder

Sn-Pb solder is the kind of solder,which was widely used in electronics industry because of its lower melting point,good wetting property and mechanical properties.It has been mainly used in the fields of electronic packaging for a long time.With the increasing awareness of people's health and environmental protection,many countries have promulgated corresponding laws and regulations to strictly limit the production and use of lead-containing products.The use of lead-free solder in the field of electronic packaging has become an irresistible trend.Through the unremitting efforts of researchers all over the world in recent decades,a series of lead-free solders have been developed.The most common lead-free solders such as Sn-Ag-Cu,Sn-Ag,Sn-Cu,Sn-Bi and Sn-Zn.Among them,Sn-0.7Cu lead-free solder has an absolute price advantage and is widely used in lead-free wave soldering,however,the solder also has some disadvantages,such as poor wettability,low tensile strength,and the melting point is higher than Sn-37Pb solder.Microalloying of lead-free solder is a very effective way to improve solder properties.This paper mainly analyzes and explores the effect of adding a small amounts of Ni and In on the Sn-0.7Cu lead-free solder to the properties of the solder and the microstructure of the solder joint.In order to study the effect of the addition of trace amount of Ni and In elements on the thermal behavior of Sn-0.7Cu binary eutectic lead-free solder,Sn-0.7Cu-xNi?x=0,0.1,0.25,0.5 and 1.0 wt.%?and Sn-0.7Cu-0.1Ni-xIn?x=0,0.5,1.0 and 2.0wt.%?solders were analyzed by DSC differential thermal analysis.The results show that the addition of Ni has an effect on the melting point of Sn-0.7Cu solder.It is not obvious,but it can significantly reduce the undercooling of the material.The addition of 1.0 wt.%Ni reduces the undercooling degree of Sn-0.7Cu solder by 20.4 ^oC;the addition of In element reduces the melting point and undercooling of the solder.Degree,in which 2.0 wt.%of In element was added,the melting point of Sn-0.7Cu-0.1Ni solder was lowered by 6.3 ^oC,and the degree of undercooling was decreased by 11.2 ^oC.The microstructure of Sn-0.7Cu-xNi and Sn-0.7Cu-0.1Ni-xIn solder alloys were observed by scanning electron microscopy?SEM?.It was found that the?-Sn grains in the microstructure of the solder alloys were refined after adding a small amount of Ni element.And a larger size of?Cu,Ni?₆Sn₅ compound was formed;after adding a small amount of In element,the?-Sn crystal grains are also refined and more?Cu,Ni?₆Sn₅ compound was produced,and the energy spectrometer?EDS?was obtained.Microscopic analysis did not reveal the formation of intermetallic compounds?IMC?containing In.The micro-lap shear test of Sn-Cu-Ni/Cu solder joints shows that the shear strength of the solder joint increases with the increase of Ni content,and the fracture type is ductile fracture.After observing and measuring the IMCs at the solder joint interface,it was found that the addition of trace amounts of Ni increased the thickness of the interface IMC layer,and the morphology of the IMC layer changed from scallop to particle accumulation,and significantly inhibited the growth of Cu₃Sn interface compounds.IMC grain size measurement shows that the addition of0.1 wt.%Ni has a significant inhibitory effect on the grain size of IMC,and the IMC grain size decreases with the increase of Ni content.The addition of In element did not significantly inhibit or promote the growth and grain size of the IMC at the Sn-0.7Cu-0.1Ni/Cu solder joint interface.The interface IMC was tested by EDS and there was no In element was detected in the interfacial IMC of solder joints.The elements are evenly distributed in the solder matrix.The wetting and spreading test of Sn-0.7Cu-0.1Ni-xIn solder alloy on Cu substrate shows that the wetting and spreading properties are greatly improved after adding a small amount of In element to Sn-0.7Cu-0.1Ni solder.When the In content is 1.0 wt.%,the wet spreading area is increased by nearly 60%compared to the Sn-0.7Cu-0.1Ni solder.