| It has become an inevitable trend at home and abroad that lead-free solders were used in electronics,information and other fields.But research on lead-free solders mainly concentrated in component selection,as well as the effect of trace element on various properties.Preparation conditions of lead-free solders were less concerned about.While liquid-solid hereditary about structure had been noted in material production and research practice.As the breakthrough point, this paper was focused on the relevance of Sn-based lead-free melt (Sn-8Zn-3Bi,Sn-17Bi-0.5Cu, Sn-5Cu) structure with solidification structure and wettability.The contents and result are shown as follows:Firstly, Temperature and time dependence of electrical resistivities of liquid base of Sn lead-free alloys with different components was surveyed by the resistivity experiments.Different characteristics and patterns of abnormal changes along with various alloys were found on p-T curves.The result come about structural transition in alloy melts by temperature. In the DSC experiments also verify the conclusion.Secondly, Refined eutectic solidification structure might result from irreversiblepost-transition melt.This might be due to smaller clusters hindering nucleation inthe melt,resulting in lower supercooling degree and higher nucleation rate.Thirdly, The solder obtained from irreversible structural transition melt had more advantage in wettability, the spreading area of the solder alloy have improved,the wetting angle have decresed and the alloy welding joint interface layer more thinner. These advantages might be owing to that faster melting, lower melt viscosity of new solder that favorable for spreading, and smaller size of the clusters lead to slower growth of compound layer. At the same time, The capability of mechanics of the solder have improved.Perspection from melt structure to explore a new preparation process of lead-free solder is obvious technological innovation. |
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