Spontaneous Tin (Sn) Whisker Growth from Electroplated Tin and Lead-Free Tin Alloys Coatings: A Short Review

Since the environmental regulations of Reduction of Hazardous Substances (RoHS) directive came into effect in Europe and Asia on July 1, 2006, requiring the removal of any lead (Pb) content from the electronics industry, the issue of tin (Sn) whisker growth from pure Sn and SnPb-free alloys has become one of the most imperative issues that need to be resolved. Moreover, with the increasing demand for electronics miniaturization, Sn whisker growth is a severe threat to the reliability of microelectronic devices. Sn whiskers grow spontaneously from an electrodeposited tin coating on a copper substrate at room temperature, which can lead to well-documented system failures in electronics industries. The Sn whisker phenomenon unavoidably gives rise to troubles. This paper briefly reviews to better understand the fundamental properties of Sn whisker growth and at the same time discover the effective mitigation practices for whisker growth in green electronic devices. It is generally accepted that compressive stress generated from the growth of Cu6Sn5 intermetallic compound (IMC) is the primary driving force for Sn whisker growth during room temperature storage. It is, therefore, important to determine that the relationship between IMC growth and Sn whisker growth. Reduction of stress in the IMC layer can therefore reduce the driving force for whisker formation and be used as a means for whisker mitigation. To date, there are no successful methods that can suppress the growth of Sn whisker as efficient as Pb addition. It is hoped that the Sn whisker growth mechanisms are understood better in the future, with better measuring and monitoring methodologies and systems being developed, the real solutions may be eventually developed to eliminate or mitigate the Sn whisker problems of green reliability lead-free electronic assemblies.

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Sn Whiskers Nucleation and Growth - Short Review

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.280.175 ◽

2018 ◽

Vol 280 ◽

pp. 175-180

Author(s):

N. Mohd Mokhtar ◽

Mohd Arif Anuar Mohd Salleh

Keyword(s):

Compressive Stress ◽

Whisker Growth ◽

Microstructural Characterization ◽

Short Review ◽

Hazardous Substances ◽

Lead Free ◽

Whisker Formation ◽

Sn Whisker ◽

Sn Whiskers ◽

Aerospace Applications

Sn whisker growth on Cu substrate Pb-free solder is a serious problem in electric and electronic devices and as well as in aerospace applications. Due to the concern on the toxicity of lead by Restriction of Hazardous Substances Directive (RoHS), new lead free materials have been developed, and this resulted in the resurfacing of Sn whisker. The compressive stress, corrosionand surface oxide have been identified as the driving force for Sn whisker formation induced by mechanical alloying and oxidation. In this paper, we report the study to understand the mechanism of Sn whisker growth that control whisker formation on Sn finished.Based on the review, a preliminary conclusion has been made, where the analysis of the topography and microstructural characterization can be determined by evaluating under various environmental influences.Furthermore, the whisker growth happening on lead-free soldered can be considerably reduced by controlling the compressive stress in the solder which initiates the growth of intermetallic compounds (IMCs).

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The origin of driving force for the formation of Sn whiskers at room temperature

Journal of Materials Research ◽

10.1557/jmr.2007.0402 ◽

2007 ◽

Vol 22 (11) ◽

pp. 3226-3232 ◽

Cited By ~ 13

Author(s):

Shi-Bo Li ◽

Guo-Ping Bei ◽

Hong-Xiang Zhai ◽

Zhi-Li Zhang ◽

Yang Zhou ◽

...

Keyword(s):

Mechanical Alloying ◽

Compressive Stress ◽

Driving Force ◽

Room Temperature ◽

Whisker Formation ◽

Sn Whisker ◽

Spontaneous Growth ◽

Sn Whiskers

Sn whiskers can form at room temperature on the agglomerated flakes produced by mechanical alloying (MA) of Ti, Sn, and C powders, whether the flakes are stored in air or water. The Sn whiskers forming in air are tens of micrometers to several centimeters in length and 0.5 to ∼10 μm in diameter. Whereas a large amount of Sn polyhedra forms on the flakes that are stored in water, a small amount of Sn whiskers forms on the polyhedra. The driving force for Sn whisker formation is the compressive stress induced by mechanical alloying (MA) and oxidation. The mechanism about the spontaneous growth of metal whiskers is discussed.

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Influence of Quantifiable Extrinsic Stresses on Tin Whisker Growth

Volume 1: 22nd Biennial Conference on Mechanical Vibration and Noise, Parts A and B ◽

10.1115/detc2009-87849 ◽

2009 ◽

Cited By ~ 3

Author(s):

Chad L. Rodekohr ◽

George T. Flowers ◽

Michael J. Bozack ◽

Robert N. Dean ◽

Robert L. Jackson ◽

...

Keyword(s):

Thin Film ◽

Stress Condition ◽

Whisker Growth ◽

Hazardous Substances ◽

Tin Whisker ◽

Sn Whisker ◽

Sn Whiskers ◽

Large Numbers ◽

Al Thin Film ◽

Film Substrate

Implementation of Restriction of Hazardous Substances (RoHS) directives regarding lead (Pb)-free electronics has resulted in the use of Pb-free and tin (Sn)-rich films as board finishes. These films pose serious reliability issues due to spontaneous Sn whisker growth formerly mitigated by the presence of Pb. Tangential compressive stress within thin films has long been cited as a principal cause of whisker growth, but there have been few direct stress measurements reported in the literature. In this study, we have manufactured two precision devices to impose eight known tangential (compressive and tensile) stress levels on Sn/Aluminum (Al) thin film/substrate systems. The results show that large numbers (∼ 103/cm2) of Sn whiskers are present on films subjected to both compressive and tensile extrinsic stresses and the lowest whisker risk occurs in films near the zero stress condition.

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Driving force for Sn whisker growth in the system Cu–Sn

Applied Physics Letters ◽

10.1063/1.2953973 ◽

2008 ◽

Vol 93 (1) ◽

pp. 011906 ◽

Cited By ~ 89

Author(s):

M. Sobiech ◽

U. Welzel ◽

E. J. Mittemeijer ◽

W. Hügel ◽

A. Seekamp

Keyword(s):

Driving Force ◽

Whisker Growth ◽

Sn Whisker

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Effect of Environment on Sn Whisker Growth during Welding of Electronic Wires

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1110.235 ◽

2015 ◽

Vol 1110 ◽

pp. 235-240 ◽

Cited By ~ 1

Author(s):

Tomomi Sakakida ◽

Tatsuo Kubouchi ◽

Yasuyuki Miyano ◽

Mamoru Takahashi ◽

Osamu Kamiya

Keyword(s):

Energy Balance ◽

Weld Metal ◽

Whisker Growth ◽

Weld Zone ◽

Electrolytic Capacitor ◽

Sn Whisker ◽

Sn Whiskers ◽

Weld Metal Microstructure ◽

Short Circuits ◽

Metal Microstructure

In Pb-free Al-Sn welding of electrolytic parts, single-crystal Sn whiskers easily form and can cause problems such as short circuits. Here we report that the growth of Sn whiskers in the weld zone of Al electrolytic condenser leads was suppressed in a vacuum environment. We examined the effect of the environment and weld metal microstructure in order to understand how to control and prevent whisker growth. In vacuum, the weld zone did not form whiskers after more than 100 h, whereas in air, whiskers grew within several hours. This suggests that whiskers require oxygen to form. The growth can be explained by the energy balance between the potential energy of the weld metal and the surface energy of the whisker. Our results will contribute to developing techniques for suppressing the formation of Sn whiskers during the percussion welding of Al electrolytic capacitor leads.

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Sn Whisker Growth in Cu(Top)-Sn(Bottom) Bilayer System upon Room Temperature Aging

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.785-786.918 ◽

2013 ◽

Vol 785-786 ◽

pp. 918-923 ◽

Cited By ~ 1

Author(s):

Lin Huang ◽

Xue Nian Lin ◽

Ren Wu Chen ◽

Jiang Yong Wang

Keyword(s):

Room Temperature ◽

Whisker Growth ◽

X Ray Diffraction ◽

Sn Whisker ◽

X Ray ◽

Bilayer System ◽

Room Temperature Aging ◽

Sublayer Thickness ◽

Temperature Aging ◽

Scanning Electron

The Sn whisker growth in Cu(top)-Sn(bottom) bilayer system upon room temperature aging was investigated by scanning electron microscope and X-ray diffraction techniques. The experimental observations indicate that the Sn whisker growth on the Cu surface in Cu-Sn bilayer system is different from that on the Sn surface in Sn-Cu bilayer system. When the Sn sublayer thickness is less than 0.5μm, the Sn whisker growth can take place in Cu-Sn system but not in Sn-Cu system. An explanation for Sn whisker growth in Cu-Sn bilayer system is given.

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Preliminary Study on Deformation and Recrystallization Behavior of Pure Tin for Mitigation of Whisker Growth

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.273.107 ◽

2018 ◽

Vol 273 ◽

pp. 107-111 ◽

Cited By ~ 1

Author(s):

Noriyuki Kuwano ◽

Marina Binti Lias ◽

Nur Azmah Binti Nordin ◽

Youhei Soejima ◽

Ahmad Rafiqan bin Nayan

Keyword(s):

Growth Process ◽

Room Temperature ◽

Whisker Growth ◽

Recrystallization Behavior ◽

Sn Whisker ◽

Continuous Growth ◽

Stable Boundary ◽

The Matrix ◽

Small Grains ◽

Preliminary Study

Since the mechanism of Sn-whisker growth is closely related with the behavior of deformation and recrystallization, understanding of the behavior is very important to establish the measure for mitigation of whisker growth. In this work, microstructural changes after heavy deformation by scratching were characterized by EBSD for a single crystal of β-Sn, and the following results were obtained. Three types of crystal grains appear immediately after the deformation; small grains in aggregation, large serrated grains and rim-grains. The small grains are considered to be formed by dynamic recrystallization. They continue to grow at a room temperature over a lengthy period of time. The large grain has a certain crystallographic relationship with the matrix where <100> axes of the large grain and the matrix are almost parallel to each other. The serrated boundaries of large grain are so stable that the large grain does not show a grain growth process. The stable boundary is considered to promote a continuous growth of whiskers.

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