Effect Of Alloy Element Addtion On IMC At The Soldering Interface Of Sn-based Binary Solders

Because of the lead and lead contained compounds' toxicity to human body and the environment and the restriction of legislation, solders without lead have become the tendency of the electronic packaging's correlated welding. At present, most of the lead-free solders are Sn-based binary or ternary alloys with adding non-toxic and non-volatile elements, such as Ag, Zn, Cu, Bi, In and so on. But in the application process of lead-free solders there are many problems, one typical question is the thick Cu-Sn intermetallic compounds (IMCs) formed due to the rapid react between Sn from the Sn-based lead-free solders (Sn concentration above 90%) and the traditional Cu substrate. And thick Cu-Sn IMCs may reduce the mechanical, metallography and the thermal fatigue performances of electronic products, and correspondingly reduce the service life of the products. So to reduce the thickness and enhance the performance of IMC are important. At the same time, it has been reported that the addition of rare earth elements has the good effects on solder alloy, and suppress the growth of IMC at the interface.It is indicated that the additions of alloy elements have much influence on the thickness and performance of the interface IMC of the Sn-based binary solders joints. In order to facilitately discuss the influence on the formation and the characteristic of the interface IMC by alloy element, in this paper we add several kinds of alloy elements (Cu, Ag, Au, rare-earth element Ce and so on) to pure Sn to prepare Sn-Cu, Sn-Ag, Sn-Au and Sn-Ce binary lead-free solders. Then we focus on the effect on the formation of the interface IMC, the organizational structure, morphology and the growth kinetics of the Sn-based binary solder/(Cu or Ni) joints by the addtion of the alloy elements. The findings indicated that:1, The addition of Cu, Ag, Au and rare-earth element Ce can reduce the IMC thickness and tremendous influence the morphology of the IMC. When the substrate is Cu, the order of the element to suppress the growth of the IMC is Ag, Cu, Ce and Au; and when the substrate is Ni, the order is Ag, Ce, Au and Cu.2 When Sn-xCu reacted with Ni substrate, the composition and the morphology of the IMC have remarkable changed. When the Cu concentration is below 0.3 wt. %, a continuous (Cu_xNi_1-x)₃Sn₄ formed at the interface. When the Cu concentration is 0.7 wt. %, bigger facet (Cu_xNi_1-x)₆Sn₅ IMCs are found on the (Cu_xNi_1-x)₃Sn₄ IMCs layer. At higher Cu concentrations (0.9-1.5 wt. %), stick shaped (Cu_xNi_1-x)₆Sn₅ compounds are detected and (Cu_xNi_1-x)₃Sn₄ IMCsdisappear. The growth rate of (Nii.xCu^Sns IMCs is determined by the CugSns content or its volume fraction. According to the present results, the threshold of Cu content in the Sn-xCu solders for the evolution from (CuxNi|.x)3Sn4 to (CuxNi|.x)6Sn5 compounds would be different under different soldering or bonding methods.3^ The adsorption of Ag3Sn particles on the surface of Cu6Sn5 IMCs was found during the reflow process of Sn-3.5Ag and Cu substrate at 260, 280 and 400°C. The soldering time and temperature has a great effect on the size of adsorbed Ag3Sn particles. When soldering at a lower soldering temperature (260, 280°C), the average size of the Ag3Sn particles has decreased with increasing soldering time. And at higher soldering temperature (400°C) the average size of the Ag3Sn particles increases rapidly with increasing soldering time.