| To meet the requirement of environmental protection, lead-free solder is developed with promising market potential as environment friendly solder. At present, investigation about lead-free solder alloy is tendency of multicomponent alloy, the interaction among components of the solder becomes more complex, experimental "trial and error" approach is difficult to systematically fulfill solder study. On the other hand, alloy molten thermodynamics is fundamental science of component systems, material composition and interaction for alloy molten, which is an important basic theory for material researching and development. Because of the complexity and equipment of experiment being very difficult to guarantee good accuracy under high-temperature, high-temperature experiment is still limited in testing thermodynamics property of alloy molten at present. Therefore, thermodynamic data about ternary and multi-components solder alloy system experimentally determined are limited, and much thermodynamic data has not been determined. On the other hand, business thermodynamic database about lead-free solder alloy is very expensive and it is difficult to apply directly in study. Therefore, with the theoretical calculations, it is very necessary and meaningful to predict thermodynamic properties of molten solder alloy, and to guide the study about lead-free solder as well.In this paper, using Miedema model, combined with Chou model, molten thermodynamic parameters of major lead-free Tin-based solder alloy system was calculated, analyzed and evaluated. And wettability, melting temperature, surface tension, and interfacial microstructure about lead-free solder was theoretically analyzed from theory of molten thermodynamic as well.Formation enthalpy for major binary tin-based solder alloy system was calculated, using Miedema model and MAEAM, respectively, in which, difference between predicted value from Miedema model and measured values is less than2KJ mol"1,which indicate that Miedema model, has a good prediction. In spite of relating to specific alloy structure, thermodynamic calculated value from MAEAM model is significantly less than that of measurement. Moreover, free energy for the ternary tin-based solder alloy system was calculated, using Miedema model, combined with Chou model, the calculation model has higher accuracy.Based on free volume theory, excess entropy of binary Tin-based alloys were calculated, using Miedema model, and found that model has a greater deviation between the calculated values and measured values.Therefore, predicted values can not apple in the thermodynamic calculations about higher temperatures condition.Based on the Miedema model, activity, activity coefficient and activity interaction coefficients of component for major binary and ternary lead-free solder alloy system were calculated and found that the activity coefficient from calculations can basically reflect the interaction between solute atoms and solvent atoms. When element interaction among the components of the solder, is too complicated, due to the limitations of Miedema model itself, predictive value could be greater of the deviation, however, based on calculating and theoretical analysis about activity interaction coefficient of the ternary lead-free solder alloy system, the prediction model has good precision.Effect of trace elements Pb on wettability of Sn-9Zn solder was investigated through experiments, and found that Pb can decrease wetting angle of Sn-9Zn solder alloy, and increase wetting area, which improve wettability of Sn-9Zn solder. Based on Butler equation, surface tension liquid solder of Sn-Zn, Sn-Pb and Sn-Zn-Pb solder alloy systems was calculated using Miedema model with Chou model, values calculated the model is very similar to measured values not only in the magnitude aspect but also trend in aspect. Based on the calculating from whole range of Pb and Sn-rich side in the Sn-Zn solder, Pb can decline surface tension of the solder, which improve wettability of Sn-Zn-Pb solder ternary alloy system.Effect of trace rare earth elements La on microstructure, interfacial microstructure between the solder and Cu substrate and microhardness for Sn3.OAgO.5Cu solder was investigated through experiments, and found that La do not change component phase of the solder, however, microstructure of the solder significantly fine and thickness of Cu6Sn5compounds the solder/Cu at the interface decrease, the interface morphology becomes flat at the same time. Moreover, microhardness of Sn3.OAgO.5Cu solder increased14.3%, reaching to25HV. From the component activity coefficient and activity interaction coefficient, thermodynamic properties of Sn-Ag-Cu-La quaternary alloy system was calculated and find that strong interaction trend between La and the component of Sn, Ag and Cu respectively, can significant fine microstructure of the solder, and reduce the growth driving force of intermetallic compounds for Cu6Sn5of Cu6Sn5/Cu interface at same time.Effect of the external magnetic field on melting temperature for Sn-9Zn solder was investigated through experiments, and found that0.45T static steady magnetic field can drop melting temperature of Sn-9Zn solder alloy to nearly2℃.Comparing to no magnetic field to the solder, the potential barrier overcome by the atoms migration from the liquid phase to the solid phase is increase, which lead to the solder melting point drop. |
PDF Full Text Request