| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程學系 === 102 === The flux has been widely used for soldering in the electronic package, since the flux can effectively remove the oxidation layer of the molten solder and ensure a good wetting during the reflow process. However, after the reflow process, the residual flux will cause the life-time degradation of the solder joints. Therefore, developing the fluxlessreflow process is an important issue for the IC package industry.
In this study, without using flux, the Sn-based solders (SnCu, SnNi) were reflowed on the PCB with ENIG (Cu/Ni(P)/Au) and ENEPIG(Cu/Ni(P)/Pd/Au).We found that all solders show reasonably good wetting on the ENIG and ENEPIG substrate at relatively high temperature, above 330 C. The surface area become wider during wetting. At this moment, the surface energy increase and very unstable. For reach a stable status, Solder by changing the structure of surface or surface segregation to reduce the surface energy. We can observe that many solid segregated in solder. Therefore, we believe that solder by segregating compound in solder to reduce surface energy.
For these results, Compounds precipitated in solder matrix during wetting caused viscosity of solder increase; at the same time, surface tension increase. Higher surface tension of solder will generate higher cohesion of molten solder, leading to poor wettability. Therefore, compound in solder matrix cause poor wettability during wetting.
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