Appearance Of Whiskers Research Articles

Study of Hillock and Zinc Whisker Evolution in Five Different Cable Tray Coatings

The main objective of this work is the study of the hillock and zinc whisker evolution of five different commercial zinc coatings applied on the same base steel wires of the patented EASYCONNECT system cable trays manufactured by VALDINOX Ltd.: white zinc alkaline electrolyte, yellow zinc trivalent electrolyte, acid zinc electrolyte, hot dip galvanized, and zinc nickel coating. The limited literature on the subject is summarized, and then the coating thickness, chemical composition, hardness and surface rugosity are characterized. The hillock and whisker density evolution are evaluated over a period of 12 months, considering the presence of compression bending stresses. It is concluded that the white alkaline and yellow trivalent coatings are the most affected, while the zinc-nickel shows the best behavior with no presence of whiskers; the acid zinc electrolyte also shows good results despite the delayed appearance of whiskers from the ninth month; the hot-dip galvanized coating does not show any presence of zinc whiskers or hillocks.

Corrosion properties of tin–copper alloy coatings in aspect of tin whisker growth

Abstract The appearance of corrosion at elevated temperature and humidity conditions could also be responsible for the growth of tin whiskers. In this paper the relation between the corrosion of different tin–copper alloys (0–5 wt.% Cu) and whisker growth was investigated. The alloys, applied as surface coating on copper base, were stored at an elevated temperature and humidity condition (85 °C/85% RH). It was observed that the tin–copper alloys show differences in the tendencies of the whisker growth. Polarisation measurements were performed to find a relation between whiskering behaviour and corrosion resistance of the alloys. The corrosion behaviour of the layers was also studied by cross-sectioning with a focused ion beam. The series of tests have shown that the whisker appearance probability of different alloys is affected by three different factors: corrosion resistance of the surface finishing, expansion rate of the corrosion product and recrystallization speed of the metal/alloy.

Whisker growth on annealed and recrystallized tin platings

The aim of this research is to examine the effects of annealing and recrystallization of electroplated tin layers on mitigating the growth of tin whiskers. Tin plating electroplated on copper substrate has been tested. Three different groups of samples have been investigated: reference, annealed and recrystallized. Three types of ageing were being used to accelerate the whisker appearance: two life-like circumstances with a constant elevated temperature in low humidity and a temperature cycling test. The whisker growth was observed by using scanning electron microscopy and was evaluated by the average and maximum whisker length and the average whisker density. It is shown that at different ageing temperatures whisker appearance and growth are decreasing in aspect of the applied pre-treatments. The effects of the pre-treatments were explained by changes of the grain structure in the tin layer which were observed with focused ion beam.

Effect of strongly oxidizing environment on whisker growth form tin coating

The effect of a strongly oxidizing environment (105°C/100%RH) on tin whisker formation has been studied with Ni and Ag underlayered samples between the tin surface coating and the bronze base material of the electronic components leads. Using nickel or silver underlayer between the copper substrate and the tin coating can be useful for preventing whiskers. The underlayer blocks the formation of Cu6Sn5 intermetallics which is one of the root causes of whisker growth. The silver underlayered samples started extreme whiskering after 2200h; on the Ni underlayered samples only hillocks have been observed. The shape of the whiskers did not resemble to the usually known whisker appearance. The oxidizing environment creates tin-oxide fast and causes thick layers of SnOx to appear on the surface of the samples and also on the whiskers. This caused the periodic appearance of large amounts of whiskers; but it blocks the length of them. This combined effect results in only large amounts of short whiskers and even causing the thickness of the tin layer to shrink by 80%. The series of tests has also showed that the nickel underlayered samples resisted whiskering better than the silver underlayered samples.

高温高湿条件下におけるはんだウィスカの成長機構

Corrosion is recognized as one of the potential drivers of whisker growth in regards to high-tin alloys. In this study, the growth of whiskers was observed for a period of 5000 hours on Sn3.0Ag0.5Cu (SAC305) as a function of soldering method under the environmental conditions of high temperature and humidity of 85°C/85%RH, 60°C/90%RH, and 40°C/95%RH. The soldering methods used were dip soldering, hand soldering with flux-cored wire, and reflow soldering with solder paste with all of the methods using commercially available flux formulations. The test pieces were examined at regular intervals for the onset of whisker growth, whisker density and maximum whisker length. In addition, samples were taken periodically for the measurement with the extent of corrosion and correlations between corrosion and whisker growth being explored. Findings presented in this paper can be summarized as follows: (1) Whiskers occurs at 85°C/85%RH and the growth rate, is two to four times greater than that at 60°C/90%RH and approximately ten times greater than that at 40°C/95%RH; (2) There is a positive correlation between whisker density and maximum whisker length; (3) For the dip soldering, a positive correlation between the average percentage of the corroded cross−sectioned region and the maximum whisker length suggests that corrosion is a driving force of whisker growth; (4) Different soldering methods resulted in varying degrees of copper erosion along with different distribution of flux residues, and subsequently different rates and locations of corrosion. It is concluded from these observations that the soldering method as well as the type of flux gives significant influence on the subsequent corrosion when exposed to high temperature and humidity conditions. Consequently, this also gives extensive effects on the onset time of whisker appearance and maximum whisker length.

Prevention of microparticle blocking in activated carbon membrane filtration with carbon whisker

We have developed activated carbon membranes (ACM) that can remove not only particulate matters but also dissolved organic matters. Recently, we succeeded in growing carbon whiskers on activated carbon membranes (W-ACM). We hypothesize that the whiskers prevent the flux from lowering due to particle blocking on the membrane surface. In this study, we compared the filtration properties and blocking characteristics of ACM and W-ACM using an artificial microsphere (polymethyl methacrylate) (PMMA), particle diameter = 0.8, 5, and 10 μm) to estimate the effect of whiskers on particle filtration. We found that the whiskers successfully prevented a reduction of penetration flux in all particle diameters; however, the prevention mechanism seems to be different according to the filtrated particle size. To clarify the mechanism, we performed numerical model analysis using a microfiltration model. In the case of 0.8 μm particle filtration, whiskers seemed to inhibit the packing of particles into the microholes existing at the surface of activated carbon membrane, and with 5–10 μm particle filtration, the packing density of the cake layer accumulated on the membrane would be reduced with the appearance of whiskers.

Growth of Zinc and Cadmium Whiskers from the Vapour Phase on a Single Crystal Substrate of the Same Material

AbstractA determination is made of the crystallographic orientation of zinc and cadmium whiskers grown on single crystal substrates of the same substances which have well‐formed faces, edges and tips. Zinc and cadmium whiskers grown in this way in the presence of hydrogen or argon are oriented as 〈1120〉, however zinc whiskers grown in vacuum have the orientation 〈1123〉. These are in fact the directions of the screw dislocations in the lattice. These and other results indicate that the whiskers grow preferentially via a screw dislocation mechanism. Some cases are observed in which zinc “whiskers” grow at large supersaturations without involving a surface diffusion mechanism as required by the classical theory of whisker growth. Possible causes for the appearance of whiskers on a single crystal substrate are discussed, as well as the factors which determine their orientation.

Beryllium Oxide Whiskers and Platelets

Beryllium oxide platelets and whiskers have been grown by heating beryllium metal in a silica furnace tube and boat with a hydrogen atmosphere for 16 hr at 1500°C. Three distinct types of whiskers formed: one type was parallel to the crystallographic c axis, another in the basal plane ([1̄010] direction), and the third in an intermediate direction (approximately the [3̄032] direction). The first type are called ``flagpole'' whiskers because they are topped by small balls of metallic appearance; they grew at the site of the original metal charge. These whiskers have pores along their axes, except in rare instances in which, instead of a pore, a whisker may have disconnected voids along its axis. Their axial growth rate was not observed directly, but was at least 0.02 μ/sec. The other two types have the more normal whisker appearance and grew at a distance of from 2 mm to 2 cm from the original metal charge. They have no pores or voids. Their growth rate was at least 0.2 μ/sec. The larger platelets, which grew in the vicinity of the normal whiskers, were long in [1̄010] direction and wide in the [0001] direction. Some of the very smallest platelets grew in the basal plane. A mechanism of growth for the flagpole whiskers is proposed. It is assumed that molten beryllium balls are splashed onto a BeO substrate, and then react with water vapor to form whiskers which push the balls away from the substrate. The normal whiskers and platelets grew at a distance from the beryllium metal, and therefore their growth involves a vapor transport mechanism.