Harsányi, Electrochemical migration behaviour of Cu, Sn, Ag and Sn63/Pb37. Kim, Influence of electrochemical properties on electrochemical migration of SnPb and SnBi solders. Ambat, Electrochemical migration on electronic chip resistors in chloride environments. Matsunawa, Electrochemical migration tests of solder alloys in pure water. Some candidate strategies for slowing down dendrite growth for tin and tin-based solder alloys have been elaborated. This work reviews briefly recent advances in method of inhibiting the ECM of tin and tin-based solder alloys. Some methods have been proposed to prevent the ECM behavior of tin-based solder alloys. Presently research effort to make clear the mechanism, kinetics, and effect of environmental factors on the ECM is the current focus of research and industrial community. Presence of moisture, ionic pollutants, bias condition, spacing between the adjacent conductors, and chemistry of electrolyte significantly affect ECM behavior. ECM can be divided into four basic steps: path formation, anodic dissolution, ion migration, and deposition of metal ions. The etching reagent carves out differences in concentration that occur during solidification.With the trend towards miniaturization and high density in electronics, electrochemical migration (ECM) of tin-based solder alloys is becoming an increasingly serious issue, causing the occurrence of short circuit and resulting in huge damage. In a metallographic grinding section, dendrites can be made visible by means of etching (s. Chalmers, dendrites only grow in undercooled melts, the directions of growth are always oriented strictly cystallographically, they branch with regular spacing and only small proportions of the melt form the dendrite skeleton. Increasing undercooling will cause less branching and thus smaller dendrites ( Fig. With great wall thicknesses, the length of dendrites may be up to several centimeters and with fast cooling rates, the size of dendrites may within submicroscopic scale. The respective form of formation and orientation within the solidification structure depends on the cooling conditions (conditions of heat transport). At the end of the process, crystals with fir tree structures are obtained.ĭifferentiation is made between directed, oriented, and undirected dendrites. In many casting alloys and particularly aluminum alloys, the secondary dendrite arm spacing (SDAS) exhibits clear correlation between the solidification speed and the material strength (SDAS ~ t solidification ~ 1/R m). During continued progress of cooling of the melt, these structures extend further until they tough each other and the melt is completely solidified. The dendrite level formed first contains less alloy elements than the subsequently growing dendrite arms and the solidified melt in the residual solidification fields (interdendritic space).ĭendrites comprise stems and branches or arms the diameter and distance of these dendrite branches or arms is referred to as dendrite arm thickness and dendrite arm spacing (DAS).ĭepending on the level of growth, definition of dendritic crystals differentiates between primary, secondary, and tertiary arms. From the stem, small branching arms grow into the melt and the interdendritic spaces. Upon solidification of the melt, the first section to form is the so-named stem. In a general sense, dendrites are solidified crystals with a directional, multi-branching, tree-like structure ( Figures 1 and 2).
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