Sn Whisker Research Articles

The behavior of Sn whisker growth on Sn-0.7Cu-0.05Ni solder joint during thermal cycling

The behavior of Sn whisker growth on Sn-0.7Cu-0.05Ni solder joint during thermal cycling

Separating Nucleation from Growth Kinetics of Sn Whiskers using Thermal Pretreatment Followed by Mechanical Loading

Separating Nucleation from Growth Kinetics of Sn Whiskers using Thermal Pretreatment Followed by Mechanical Loading

Effects of ZrO2 Nano-Particles' Incorporation into SnAgCu Solder Alloys: An Experimental and Theoretical Study.

This study investigates the mechanism and effects of incorporating different ZrO2 nano-particles into SAC0307 solder alloys. ZrO2 nano-powder and nano-fibers in 0.25-0.5 wt% were added to the SAC0307 alloy to prepare composite solder joints by surface mount technology. The solder joints were shear tested before and after a 4000 h long 85 °C/85% RH corrosive reliability test. The incorporation of ZrO2 nano-particles enhanced the initial shear force of the solder joint, but they decreased the corrosion resistance in the case of 0.5 wt%. SEM, EDS, and FIB analysis revealed intensive growth of SnO2 on the solder joint surfaces, leading to the formation of Sn whiskers. Density functional theory (DFT) simulations showed that, despite Sn being able to bond to the surface of ZrO2, the binding energy was weak, and the whole system was therefore unstable. It was also found that ZrO2 nano-particles refined the microstructure of the solder joints. Decreased β-Sn grain size and more dispersed intermetallic compounds were observed. The microstructural refinement caused mechanical improvement of the ZrO2 composite solder joints by dispersion strengthening but could also decrease their corrosion resistance. While ZrO2 nano-particles improved the solder joint mechanical properties, their use is recommended only in non-corrosive environments, such as microelectronics for space applications.

Novel cable‐like tin@carbon whiskers derived from the Ti2SnC MAX phase for ultra‐wideband electromagnetic wave absorption

AbstractOne‐dimensional (1D) metals are well known for their exceptional conductivity and their ease of formation of interconnected networks that facilitate electron migration, making them promising candidates for electromagnetic (EM) attenuation. However, the impedance mismatch from high conductivity and their singular mode of energy loss hinder effective EM wave dissipation. Construction of cable structures not only optimizes impedance matching but also introduces a multitude of heterojunctions, increasing attenuation modes and potentially enhancing EM wave absorption (EMA) performance. Herein, we showcase the scalable synthesis of tin (Sn) whiskers from a Ti2SnC MAX phase precursor, followed by creation of a 1D tin@carbon (Sn@C) cable structure through polymerization of PDA on their surface and annealing in argon. The EMA capabilities of Sn@C significantly surpass those of uncoated Sn whiskers, with an effective absorption bandwidth reaching 7.4 GHz. Remarkably, its maximum radar cross section reduction value of 27.85 dB m2 indicates its exceptional stealth capabilities. The enhanced EMA performance is first attributed to optimized impedance matching, and furthermore, the Sn@C cable structures have rich SnO2/C and Sn/SnO2 heterointerfaces and the associated defects, which increase interfacial and defect‐induced polarization losses, as visually demonstrated by off‐axis electron holography. The development of the Sn@C cable structure represents a notable advancement in broadening the scope of materials with potential applications in stealth technology, and this study also contributes to the understanding of how heterojunctions can improve EMA performance.

Does Sn2+ play well with Zn2+ as their molten chloride salts react with Cr–Al–B MAB phase?

Novel Zn-MAX phases like Ti2ZnC were synthesized in the literature by the reaction between Lewis acid salts like ZnCl2 and the MAX phase. The interactions between the Cr–Al–B MAB phase contained in the PLS coating formed during HDA of Fe–Cr–B cast steel and five types of molten chloride salts (ZnCl2 and SnCl2) were investigated. The results showed that the Cr-(Al, Zn)–B and Cr-(Al, Sn)–B MAB phase solid solution were formed as the PLS coating reacted with the molten ZnCl2 and SnCl2, respectively, through topochemical reaction. Zn and Sn could not coexist in the A-site Cr–Al–B MAB phase solid solution, and the replacement ability of Sn2+ contained in molten salt was much stronger than that of Zn2+. Zn and Sn whiskers could spontaneously grow on the Cr-(Al, Zn)–B and Cr-(Al, Sn)–B MAB phase solid solution respectively.

Effects of CuO nanoparticles on SAC composite solder joints: Microstructural and DFT study

In this paper, novel application possibilities of CuO nanoparticles were investigated in SAC0307 solder alloy for composite soldering purposes. CuO nanoparticles in 0.25 and 0.5 wt% were mixed into the solder paste to produce composite solder joints. Solder joints were manufactured using standard surface mounting technology from different solder pastes. The solder joints were loaded in an 85 °C/85RH% temperature and humidity test for 4000 h. It was found that the CuO composite solder joints showed improved mechanical quality due to the microstructural refinement, which was studied using scanning electron microscopy (SEM) and focused ion beam (FIB) analysis. On the other hand, the corrosion resistance of CuO joints decreased, as they suffered localized corrosion extensively, which produced longer and more Sn whiskers on their surface than on the reference SAC0307. Density functional theory (DFT) calculations proved that CuO can bond to Sn, but CuO is not chemically inert in the solder bulk. CuO can start a cyclic reaction with the dispersed Cu6Sn5 intermetallics, which produces SnO2 in the solder bulk, ultimately enhancing corrosion. Therefore, CuO nanoparticles are suggested to be applied only in non-corrosive environments, such as space applications.

MAX phase-derived tin nano-/micro-wires with controlled diameter through seeded growth

Nano-scaled one-dimensional (1D) metallic materials show tremendous potential in various important technological applications, such as flexible transparent electrodes and catalysis. However, achieving scalable preparation of nanoscale 1D metallic materials remains a significant challenge for most metallic compositions. The phenomenon of A-site whisker growth from MAX phases provides an opportunity for innovative 1D metal fabrication techniques. However, the whisker diameters derived from MAX phases are often too large to satisfy the requirements of advanced technologies. Herein, we introduce Sn nanocrystals with different particle sizes as the initial seeds to tune the diameter of Sn whiskers, fed by the atomized tin resulted from the mechanochemical decomposition of Ti2SnC. It was found that incorporating nano-scaled (50–300 nm) and micro-scaled (0.5–1 μm) Sn crystal seeds resulted in the growth of whiskers with diameters matching the respective seed sizes, and the reduced melting point phenomenon of the nano-sized Sn wires conformed to the size-dependent behavior of metal nanowires. The diverse A-site elements within MAX phases implied that this method could be a generic strategy for synthesizing various nanoscale 1D metallic materials with controllable diameters.

Spontaneous growth of Sn whisker on the hot-dipping Al[sbnd]Sn alloy coating on Fe-Cr-B cast steel

Although the MAX phase solid solutions and spontaneous growth of Sn whiskers had been reported widely, the study on the spontaneous growth of whisker at room temperature on the MAB phase was very rare. In our previous work, the periodic layered structure consisted of alternatively arranged Cr-Al-B MAB phase and FeAl3 was formed during the hot-dip aluminizing of Fe-Cr-B cast steel. Herein, the Cr-(Al, Sn)-B MAB phase solid solution was prepared by HDA of Fe-Cr-B cast steel in a AlSn alloy melt and subsequently thermal diffusion treatment. Sn atoms in the Al melt could partially occupy the positions of Al atoms in the Cr-Al-B MAB phase by A-site replacement approach, which resulted in the formation of the Cr-(Al, Sn)-B MAB phase solid solution. Subsequently, spontaneous growth of β-Sn whisker occurred on the Cr-(Al, Sn)-B MAB phase solid solution at room temperature. The original Sn source was the pure Sn phase among the grains of Cr-(Al, Sn)-B MAB phase solid solution. The mass transport pathway for maintaining the spontaneous growth of Sn whiskers was: pure Sn among the grains of Cr-Al-B MAB phase→ Cr-(Al, Sn)-B MAB phase→ SnO2 → Sn whisker. The spontaneous growth of Sn whisker in the air resulted in the deep grooves covered on the surface of whisker, while, growth in the vacuum resulted in the prism structure at the bottom of whisker. The spontaneous growth of Sn whisker could grow from both the bottom and the tip. The findings will expand the family of MAB phase and help well understand the growth mechanism of Sn whisker.

Sn Whiskers from Ti2SnC Max Phase: Bridging Dual-Functionality in Electromagnetic Attenuation.

In the ever-evolving landscape of complex electromagnetic (EM) environments, the demand for EM-attenuating materials with multiple functionalities has grown. 1D metals, known for their high conductivity and ability to form networks that facilitate electron migration, stand out as promising candidates for EM attenuation. Presently, they find primary use in electromagnetic interference (EMI) shielding, but achieving a dual-purpose application for EMI shielding and microwave absorption (MA) remains a challenge. In this context, Sn whiskers derived from the Ti2SnC MAX phase exhibit exceptional EMI shielding and MA properties. A minimum reflection loss of -44.82dB is achievable at lower loading ratios, while higher loading ratios yield efficient EMI shielding effectiveness of 42.78dB. These qualities result from a delicate balance between impedance matching and EM energy attenuation via adjustable conductive networks; and the enhanced interfacial polarization effect at the cylindrical heterogeneous interface between Sn and SnO2, visually characterized through off-axis electron holography, also contributes to the impressive performance. Considering the compositional diversity of MAX phases and the scalable fabrication approach with environmental friendliness, this study provides a valuable pathway to multifunctional EM attenuating materials based on 1D metals.

Surface-Energy-Driven Tin Whisker Growth on Pure Tin

Spontaneous Sn whisker growth, as a reliability issue in electronic assemblies, has drawn much attention in the past several decades. However, the underlying mechanism is still ambiguous. Herein, the growth of Sn whiskers on pure Sn with different specific surface areas was studied to elucidate the effect of surface energy on Sn whisker growth. Though fabricated and cultivated using the same parameters, it was found that Sn whiskers were obtained on the sample of nano-Sn, which possesses excess surface energy, while no whiskers were observed on the sample of micro-Sn, indicating that surface energy plays a significant role in Sn whisker growth. In addition, the whiskering phenomenon is confirmed to be an abnormal recrystallization process according to the microstructure of the whisker root. Therefore, a Sn whisker growth mechanism companied with an abnormal recrystallization process is proposed, which is driven by the excess surface energy. This work provides a new perspective on understanding the long-standing Sn whiskering problem.

Corrosion problems of SAC-SiC composite solder alloys

SiC nano-fibers and nano-particles in 0.5 wt% were mixed into SAC0307 alloy. Solder joints were stored for 4000 h in 85 °C/85RH%. The SiC nano-phases decreased the corrosion resistance of the composite solder alloys and increased the Sn whisker growth. Microstructural analysis with SEM and FIB proved that whisker growth was caused by localized corrosion and intermetallic layer growth at the upper meniscus of the solder joints, which effects caused mechanical stress via volumetric changes. DFT simulations proved that although SiC could bond to Sn atoms, but the SiC is prone to corrosion, so SiC acted as corrosion incubation points in the Sn-matrix.

One-dimensional core-sheath Sn/SnOx derived from MAX phase for microwave absorption

One-dimensional (1D) metals are highly conductive and tend to form networks that facilitate electron hopping and migration. Hence, they have tremendous potential as microwave-absorbing (MA) materials. Traditionally, 1D metals are mainly precious metals such as gold, silver, nickel, and their preparation methods often have low yield and are not environmentally friendly, which has limited the exploration in this area. Herein, the unique nanolaminate structure and chemical bond characteristics of Ti2SnC MAX phase is successfully taken advantages for large-scale preparation of Sn whiskers, and then, core-sheath Sn/SnOx heterojunctions are obtained by simply annealing at different temperatures. The heterojunction annealed at 500 °C possesses favorable MA performance with an effective absorption bandwidth of 5.3 GHz (only 1.7 mm) and a minimum reflection loss value of −51.97 dB; its maximum radar cross section (RCS) reduction value is 29.59 dB·m2, confirming its excellent electromagnetic wave attenuation ability. Off-axis electron holography is used to visually characterize the distribution of charge density at the cylindrical heterogenous interface, confirming the enhanced interfacial polarization effect. Given the diversity of MAX phases and the advantages of the fabrication method (e.g., green, inexpensive, and easily scalable), this work provides significant guidance for the design of 1D metal-based absorbers.

Mitigation of metal whisker growth from MAX phases by A-site alloying strategy

The A-site alloying strategy has been recognized as an effective approach to tailor the properties of MAX phases. Herein, the whiskering behaviors on Ti2(Sn1−x, Gax)C (x = 0–1), a group of solid solutions between Ti2SnC and Ti2GaC, were investigated to explore the possibility of mitigating metal whisker growth from MAX phase by A-site alloying strategy. The whisker cultivation experiments suggested that the Ga alloying at A-site of Ti2SnC can significantly reduce the density of Sn whiskers observed on sample surface, which got completely eliminated when the ratio of Sn/Ga was lower than 0.25. Afterwards, the first principles calculation on the solution and diffusion behaviors was performed to elucidate the mitigation mechanism behind. The results implied that the Sn atoms feeding whisker can only diffuse through the Sn part of the A-element layer in Ti2(Sn1−x, Gax)C. In addition, the Sn vacancy formation energy as well as the migration barrier was found to be elevated with the presence of Ga substitution. Consequently, the diffusion paths of Sn atoms, which played a significant role in realizing the matter transfer during the whiskering process, got narrowed (reducing accessible paths) and rugged (rising motion barrier) by the A-site Ga alloying atoms in Ti2(Sn1−x, Gax)C.

Incorporation and corrosion protection mechanism of TiO2 nano-particles in SnAgCu composite alloys: Experimental and density functional theory study

This work studied the incorporation mechanism of TiO2 nano-particles into SnAgCu solders and their effect on the corrosion behavior of the composite alloy. Composite solder alloys have been made from 99Sn0.3Ag0.7Cu solder alloy and TiO2 nano-particles between 0.25 and 1 wt%. The alloys in solder joints were exposed to 4000 h long 85 °C/85RH% thermal-humidity test, and their surface was observed by SEM and FIB techniques. Large localized corrosion spots and numerous Sn whiskers have been found on the samples, except for the samples with 0.25 wt% TiO2 content. The corrosion of the Sn grains resulted in a volumetric increase and mechanical stress, which was relaxed via whisker growth. TiO2 nano-particles in 0.25 wt% incorporated layer-like at the boundaries of the Sn grain. Density functional theory calculations proved that at soldering conditions, the Sn atoms of the solder alloy could bond to the TiO2 NPs through the O atoms of TiO2. The TiO2–Sn oxide layer at the grain boundaries could suppress the corrosion of the composite solder alloys and whisker growth. In the case of higher weight fractions TiO2, the nano-particles were agglomerated and could not perform corrosion protection effect.

Effect of Isothermal Annealing on Sn Whisker Growth Behavior of Sn0.7Cu0.05Ni Solder Joint

This paper presents an assessment of the effect of isothermal annealing of Sn whisker growth behavior on the surface of Sn0.7Cu0.05Ni solder joints using the hot-dip soldering technique. Sn0.7Cu and Sn0.7Cu0.05Ni solder joints with a similar solder coating thickness was aged up to 600 h in room temperature and annealed under 50 °C and 105 °C conditions. Through the observations, the significant outcome was the suppressing effect of Sn0.7Cu0.05Ni on Sn whisker growth in terms of density and length reduction. The fast atomic diffusion of isothermal annealing consequently reduced the stress gradient of Sn whisker growth on the Sn0.7Cu0.05Ni solder joint. It was also established that the smaller (Cu,Ni)6Sn5 grain size and stability characteristic of hexagonal η-Cu6Sn5 considerably contribute to the residual stress diminished in the (Cu,Ni)6Sn5 IMC interfacial layer and are able to suppress the growth of Sn whiskers on the Sn0.7Cu0.05Ni solder joint. The findings of this study provide environmental acceptance with the aim of suppressing Sn whisker growth and upsurging the reliability of the Sn0.7Cu0.05Ni solder joint at the electronic-device-operation temperature.

Sn Whisker Growth During Mechanical Loading and Unloading: Highlighting the Critical Role of Stress in Whisker Growth

Sn Whisker Growth During Mechanical Loading and Unloading: Highlighting the Critical Role of Stress in Whisker Growth

Tin whisker growth from titanium-tin intermetallic and the mechanism

• Tin (Sn) whiskers were observed to grow out of Ti 6 Sn 5 intermetallic particles. • The critical role (as tin atom source) of Ti 6 Sn 5 intermetallic compound in Sn whisker growth is identified. • An atomic diffusion-based whisker growth model is proposed, and a new preparation method of metal nanowires is expected. Spontaneous growth of metal whiskers, represented by tin whiskers, has haunted tin-based platings and solder joints for decades and caused huge losses to the electronics industry. Despite numerous efforts, the underlying growth mechanism has been resisting interpretation, and the whiskering phenomenon even continues to expand its territory. Here, we report the growth of tin whiskers from a Ti 6 Sn 5 intermetallic. These tin whiskers share similar characteristics with those found on the platings or solder joints, but grow more and faster, with finer diameters. After tin whisker growth, Ti 6 Sn 5 retains its crystal structure, implying a dealloying process. Combining experimental and first-principles calculation results, we analyzed the growth mechanism of tin whiskers in detail, and proposed a diffusion-based growth model. The strain energy stored in Ti 6 Sn 5 during deformation provides a driving force for whisker growth, and the short-circuit diffusion paths generated by such deformation accelerate whisker growth. These findings identify the critical role of intermetallic substrate in the whiskering phenomenon, shedding new light for comprehensively understanding the whisker growth mechanisms. Furthermore, the plenty and rapid growth of tin whiskers also means a new method for the preparation of one-dimensional metallic materials.

Method for inhibiting Sn whisker growth on Ti2SnC

Method for inhibiting Sn whisker growth on Ti2SnC

Suppression of Sn whisker growth from SnAgCu solder alloy with TiO2 and ZnO reinforcement nano-particles by increasing the corrosion resistance of the composite alloy

The main joining process of the electronic industry is still soldering with different alloys of Sn. This work studied the relationship between Sn whisker growth and corrosion resistance of 99Sn0.3Ag0.7Cu–TiO2/ZnO (0.25wt%) composite solder alloys in a corrosive environment via scanning electron microscopy and focused ion beam techniques. The corrosive environment test showed that the application of TiO2 and ZnO nano-particles almost totally suppressed the Sn whisker growth and improved the corrosion resistance of the composite solder alloys compared to the reference 99Sn0.3Ag0.7Cu alloy. The microstructural analysis of the reference 99Sn0.3Ag0.7Cu solder alloy showed that the volumetric increase of the corroded β-Sn grains resulted in local mechanical stress in the solder joints, which was released by Sn whisker development. However, in the composite solder joints, the increased grain boundary fraction and segregation of the TiO2 and ZnO nano-particles to the grain boundaries resulted in a relatively uniform and compact protective oxide layer at the β-Sn grain boundaries. This suppressed the formation of SnOx, and via this, the corrosion-induced whisker growth.

An Analytical Model of Spontaneous Whisker Growth on Strain Accumulation From Contiguous Film Network

Whiskering has been a reemerging problem affecting the reliability of lead-free electronics. Although the in-layer strain has long been considered one of the major driving forces for whisker growth, the quantitative understanding of the relationship between stress and Sn whiskering is still limited. To fill this technological gap, we develop an analytical model to express the contribution of strain accumulation to the formation of whiskers. The model predicts the average whisker length by calculating the volume of Sn material reallocated by strain in a single whisker site. We apply this model to analyze strain generation (via thermal expansion mismatch, applied forces, and dynamic recrystallization (DRX) process) and strain relaxation processes (creep-law plasticity and material diffusion). The simulated average whisker length is in good agreement with multiple previous experimental data, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula> reaches 0.80 after reliable calibration. The sensitivity and uncertainty are conducted to evaluate the reliability of the model in response to variations in external input, including deposition thickness and whisker density. The amount of DRX strain is estimated based on the model results. The application and limitations of the model are theoretically analyzed and discussed.