Propriétés physiques de soudures sans plomb à l'état liquide et solide

Abstract : This work presents a contribution to the experimental study of the electronic transport properties of binary and ternary liquid alloys and to their industrial use as solders. The resistivity is a very sensitive probe of the state of materials. We used it to analyze a hysteresis effect highlighted before by Miller, Paces and Komarek. We undertook this study by carrying out thermal cycles of increasing amplitude for the Cd60Sb40 alloy. Miller Paces and Komarek allotted this phenomenon to the presence of aggregates which would persist in the liquid state. Dahlborg and al. recently studied and highlighted the influence of the history of the liquid bath on the characteristics of the solid. The solid alloy properties are different when the liquid alloy has been heated at different temperatures. Dahlborg and al. allot also this phenomenon to the existence of aggregates which would be destroyed with temperature and which according to their presence or their absence would induce a solidification of grains with different sizes and different phases. We confirmed the existence of this phenomenon and proposed another explanation. In a first stage, we measured with a vertical silica glass cell, the resistivity and the absolute thermoelectric power (ATP) of Cd1-x-Sbx alloys according to temperature and to concentration, then we deduced thermal conductivity from them. The interpretation of the experimental results over the whole phase diagram of the studied system was made by mean of the Faber-Ziman theory by using local pseudopotentials and hard spheres structure factors. We could interpret quantitatively, for the first time to our knowledge, the absolute thermoelectric power of liquid antimony. For that, we introduced a correction factor suggested by Mott that we made dependent on energy. We confirmed that in the medium of the phase diagram persisted reminiscence of characteristics of the solid semiconductor state, disappearing completely above 760°C. In a second step, we were interested in the problems arising from the replacement of traditional solders (tin - lead) by lead free solders (tin - silver - copper). This work is carried out in collaboration between the Metz University, and the Chemnitz University. A solder must conduct electricity well and dissipate heat well. In Metz, we measured the 3 resistivity (electric conductivity) and the ATP of the solders (Sn95:3Ag4Cu0:7 ; Sn96Ag4 ; Sn60Pb40 ; Sn97Cu3 ; Sn90Pb10 ; Sn96:5Ag3:5 ; Sn95Sb5), and deduced from them thermal conductivity according to temperature by employing the relations between the electronic transport coefficients. In the liquid and solid state, thermal and electrical conductivities of the lead free solders are better than those of tin-lead solders, which is wished. To carry out a good solder, it is necessary that it "runs" well and "wets well" the substrate (printed circuit). We measured the density but also the surface tension and the interfacial tension which characterize wetting, spreading and the capillary increase. We could compare the wetting of various solders on various substrates under laboratory conditions (very pure metals under vacuum and controlled atmosphere) and industrial conditions (industrial solders in air and with flux). We also carried out viscosity measurements for the compositions of the lead free solders ready to replace the traditional solder and checked the in uence of a very small quantity of nickel on the viscosity of the lead free solders characterized by a pasty solidification. To be able to make metallographic observations, we developed a technique of mixing nanocristalline powder with lead free solders. These solders are observed with various microscopes and are brie y commented.
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Souad Mhiaoui. Propriétés physiques de soudures sans plomb à l'état liquide et solide. Physique [physics]. Université Paul Verlaine - Metz, 2007. Français. ⟨NNT : 2007METZ055S⟩. ⟨tel-01775382⟩

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