M. Bizjak, M. Koprivšek - Dissolution of fuse element notches by SnCu solder and the temperature rise of fuse element

Martin Bizjak (1), Mitja Koprivšek (2), Matija Strehar (2), Viktor Martinčič (2)

Iskra MIS, d. d., Kranj(1),
ETI, d. d., Izlake(2),

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The dissolution of fuse element material in SnCu1 melt was investigated experimentally at the conditions as close to those of fuse link as possible. Test strips of E-Cu were dipped into large volume of molten SnCu1 kept at various specified temperatures in order to measure the reduction of their thickness due to the dissolution of Cu strip into SnCu1 melt. Thickness was measured by metallographic methods. Then the dissolution parameters were evaluated with the approximation of semi-infinite one-dimensional problem, where mass flux density of Cu into the SnCu1 melt determines the diffusion of Cu due to concentration difference through the solid inter-metallic layer of constant thickness. For this solute-solvent system a dissolution coefficient K is evaluated concerning the Arrhenius law for its temperature dependence. The actual temperature, at which M-effect takes place in fuse element, was assessed by computer simulation of its thermal steady state at the over-current of fuse blow. The dissolution process is considered to evolve over the consecutive steps of stationary conditions till the final rupture of the notch, so the initial thermal state is calculated when solder just melts and the final pre-rupture state where the notch is just dissolved. The relative magnitude of coefficient K was assessed along the segments adjacent to the rupturing site for the purpose to give us an insight into the phenomenon of abnormal M-effect.

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