Tin whisker growth from electroplated finishes – a review

Bunyan, D; Ashworth, Mark; Wilcox, G.D.; Higginson, R.L.; Heath, Richard J.; Liu, C

doi:10.1179/0020296713z.000000000119

Cited by 19 publications

(15 citation statements)

References 33 publications

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“…MW concentrations are small compared to the surface concentration of grains, (say, by a factor of 10 −3 − 10 −5 ) varying exponentially between different local regions on the metal surface; 7,8,[10][11][12]25 some of the nominally identical samples may exhibit no MW, others showing significant MW infestations. Growing or eliminating MW 'on demand' remains practically impossible, which aggravates the reliability concerns.…”

Section: Introductionmentioning

confidence: 99%

Microscopic Structure of Metal Whiskers

et al. 2018

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We present TEM images of the interior of metal whiskers (MW) grown on electroplated Sn films. Along with earlier published information, our observations focus on a number of questions, such as why MWs' diameters are in the micron range (significantly exceeding the typical nano-sizes of nuclei in solids), why the diameters remain practically unchanged in the course of MW growth, what is the nature of MW diameter stochasticity, and what is the origin of the well-known striation structure of MW side surfaces. In an attempt to address such questions we performed an in-depth study of MW structure at the nanoscale by detaching a MW from its original film, reducing its size to a thin slice by cutting its sides by a focused ion beam, and performing TEM on that structure. Our observations revealed a rich nontrivial morphology suggesting that MW may consist of many side by side grown filaments. This structure appears to extend to the outside whisker surface and be the reason for the striation. In addition, we put forward a theory where nucleation of multiple thin metal needles results into micron-scale and larger MW diameters. This theory is developed in the average field approximation similar to the roughening transitions of metal surfaces. The theory also predicts MW nucleation barriers and other observed features.PACS numbers:

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Section: Introductionmentioning

confidence: 99%

Microscopic Structure of Metal Whiskers

et al. 2018

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“…A comprehensive review of experimental data on the most studied tin whiskers before the year of 2003 was given in a monograph 15; Refs. [16][17][18]20 provide more recent summary.…”

Section: Fig 1: Sem Pictures Of Tin (Left) and Zinc (Right) Whiskersmentioning

confidence: 99%

“…(20) can apply as long as it is not affected by rare events terminating or exponentially slowing whisker growth. These events take place when whisker tips reach random local regions of abnormally low fields.…”

Section: Whisker Growth a General Formalismmentioning

confidence: 99%

Electrostatic Theory of Metal Whiskers

Карпов

2014

Phys. Rev. Applied

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Metal whiskers often grow across leads of electric equipment and electronic package causing current leakage or short circuits and raising significant reliability issues. The nature of metal whiskers remains a mystery after several decades of research. Here, the existence of metal whiskers is attributed to the energy gain due to electrostatic polarization of metal filaments in the electric field. The field is induced by surface imperfections: contaminations, oxide states, grain boundaries, etc. A proposed theory provides closed form expressions and quantitative estimates for the whisker nucleation and growth rates, explains the range of whisker parameters and effects of external biasing, and predicts statistical distribution of their lengths.

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“…To the contrary, for the Brownian movements, the momenta transferred from the top and bottom collisions mostly cancel each other and only the 1/ √ N fraction of them remains unbalanced as a fluctuation (we skip the details of derivation). 6: A discrete (4-side) sketch of a particle bombarded by molecules having on average the thermal velocity vT and capable of colliding with the particle when they are within the range of the mean free path l0 from it. Shown in short arrows are vertical (in the plane of figure) air currents of low velocity va that is reduced by the factor l0/d in the domain of molecules capable of colliding with the particle.…”

Section: Brownian Movements Vs Viscous Dragmentioning

confidence: 99%

Understanding the movements of metal whiskers

Карпов

2015

Journal of Applied Physics

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Metal whiskers often grow across leads of electric equipment causing short circuits and raising significant reliability issues. Their nature remains a mystery after several decades of research. It was observed that metal whiskers exhibit large amplitude movements under gentle air flow or, according to some testimonies, without obvious stimuli. Understanding the physics behind that movements would give additional insights into the nature of metal whiskers. Here, we quantitatively analyze possible mechanisms of the observed movements: (1) minute air currents, (2) Brownian motion due to random bombardments with the air molecules, (3) mechanically caused movements, such as (a) transmitted external vibrations, and (b) torque exerted due to material propagation along curved whiskers (the garden hose instability), (4) time dependent electric fields due to diffusion of ions, and (5) non-equilibrium electric fields making it possible for some whiskers to move. For all these mechanisms we provide numerical estimates. Our conclusion is that the observed movements are likely due to the air currents or electric recharging caused by external light or similar factors.

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Tin whisker growth from electroplated finishes – a review

Cited by 19 publications

References 33 publications

Microscopic Structure of Metal Whiskers

Microscopic Structure of Metal Whiskers

Electrostatic Theory of Metal Whiskers

Understanding the movements of metal whiskers

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