“…Actually, the whisker development is the stress release of the Sn layer against internal stresses, which can originate from direct mechanical load (by test needles, connectors, etc.) [6], from residual stress during deposition of the Sn layer [2], from volumetric expansion inside the layer structure (like oxide formation, intermetallic layer growth) [7], and from thermomechanical effects [8].…”
The effect of copper substrate roughness and tin layer thickness were investigated on whisker development in the case of Sn thin-films. Sn was vacuum-evaporated onto both unpolished and mechanically polished Cu substrates with 1 µm and 2 μm average layer thicknesses. The samples were stored in room conditions for 60 days. The considerable stress—developed by the rapid intermetallic layer formation—resulted in intensive whisker formation, even in some days after the layer deposition. The developed whiskers and the layer structure underneath them were investigated with both scanning electron microscopy and ion microscopy. The Sn thin-film deposited onto unpolished Cu substrate produced less but longer whiskers than that deposited onto polished Cu substrate. This phenomenon might be explained by the dependence of IML formation on the surface roughness of substrates. The formation of IML wedges is more likely on rougher Cu substrates than on polished ones. Furthermore, it was found that with the decrease of layer thickness, the development of nodule type whiskers increases due to the easier diffusion of other atoms into the whisker bodies.
“…Actually, the whisker development is the stress release of the Sn layer against internal stresses, which can originate from direct mechanical load (by test needles, connectors, etc.) [6], from residual stress during deposition of the Sn layer [2], from volumetric expansion inside the layer structure (like oxide formation, intermetallic layer growth) [7], and from thermomechanical effects [8].…”
The effect of copper substrate roughness and tin layer thickness were investigated on whisker development in the case of Sn thin-films. Sn was vacuum-evaporated onto both unpolished and mechanically polished Cu substrates with 1 µm and 2 μm average layer thicknesses. The samples were stored in room conditions for 60 days. The considerable stress—developed by the rapid intermetallic layer formation—resulted in intensive whisker formation, even in some days after the layer deposition. The developed whiskers and the layer structure underneath them were investigated with both scanning electron microscopy and ion microscopy. The Sn thin-film deposited onto unpolished Cu substrate produced less but longer whiskers than that deposited onto polished Cu substrate. This phenomenon might be explained by the dependence of IML formation on the surface roughness of substrates. The formation of IML wedges is more likely on rougher Cu substrates than on polished ones. Furthermore, it was found that with the decrease of layer thickness, the development of nodule type whiskers increases due to the easier diffusion of other atoms into the whisker bodies.
“…Similarly, formation of other low-melting metal polyhedrons, such as tin [37], was also observed. In addition, Liu's research on the growth atmosphere of whiskers found that whiskers can form prismatic whiskers surrounded by speci c faces in a non-oxidizing atmosphere [38], which shares the same mechanism to the formation of the indium polyhedrons in this work.…”
The mechanism behind spontaneous growth of metal whiskers is essential to develop lead-free whisker mitigation strategy for the sake of long-term reliability of electronics, and has been sought for several decades. However, a consensus about it still lacks, and a host of factors influencing the phenomenon have been investigated, but the role of interface energy has not been paid adequate attention. In this study, the whisker growth propensities of ball-milled Ti2InC/In and non-MAX phase TiC/In and SiC/In are comparatively studied in the terms of the wettability, thermal behavior and crystal structures. The wetting angles of indium with Ti2InC, TiC, and SiC (144.4°, 155.7°, and 142.2°, respectively) are large and quite close, indicating the poor wettability between liquid indium and the three ceramics. The thermal behaviors of all the three systems have obvious changes after ball milling. The number density of indium whiskers on ball-milled Ti2InC are significantly greater than those on the TiC and SiC substrates, which is explained based on interface energy and the crystal structure difference of the ceramic substrates.
“…Whiskers growth has been widely reported in other materials, such as, Sn or Zn crystal solders [21,22]. Whiskers growth in Sn solders can be interpreted as an atomic diffusion process where stress generation and relaxation simultaneously occurs.…”
Ti-based metallic glasses were subjected to a 20 MeV Cl 4+ ion radiation under liquid-nitrogen cooling. Their responses, as well as effects of the electronic excitation and nucleus-nucleus collision were evaluated. The collision cascade during irradiation typically changes the structure by increasing the liquid-like zone/cluster, or the content of the free volume. However, along the ion incident depth, the structure change is inhomogeneous. Numerous whiskers appear and aggregate on the side of the irradiation surface, which are several micrometers away from the edge. This corresponds with the maximum collision depth obtained by the Monte Carlo simulation, where nuclear loss plays a dominant role. Moreover, the liquid-like zone continually forms, which add to the whiskers growth and subsequent self-healing. Results suggest that the irradiation-induced local shear stress combines with the well-localized liquidlike zone results in the observed phenomena. This study demonstrates that metallic glasses have high morphological instability under ion irradiation, which assets can pave new paths for their further applications.
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