Time-lapse photography of the β-Sn/α-Sn allotropic transformation

Maio, D. Di; Hunt, C

doi:10.1007/s10854-008-9739-5

Cited by 17 publications

(11 citation statements)

References 6 publications

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“…14,15 Taking into account the 26% increase in volume of a-Sn, the theoretical R a is 15 mX. Theoretically then, the experimental resistance should not have exceeded this value.…”

Section: Electrical Resistance Modelmentioning

confidence: 98%

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Monitoring the Growth of the α Phase in Tin Alloys by Electrical Resistance Measurements

Maio

Hunt

2009

Journal of Elec Materi

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The b phase of tin is stable only down to 13°C. Below that temperature the thermodynamically stable phase is a tin, more commonly known as tin pest. This phase has gained notoriety because of the catastrophic consequences of the transforming metal. Interest in this subject increased after the transition from tin-lead to lead-free solder, driven by European restriction of the use of hazardous substances (RoHS) legislation. Lead-free alloys contain from 95% to 99% tin and could potentially be susceptible to the b/a transformation mentioned above. The nucleation of the a phase takes a long time to occur, months or even years, especially in alloys of tin. For this reason this phenomenon is particularly difficult to study. The growth, however, occurs faster, and this paper describes a procedure for observing and measuring growth based on electrical measurements. Furthermore, a sample preparation technique that considerably accelerates the nucleation in alloys is described. Seven binary alloys were tested with this procedure and ranked in terms of their propensity to transform. Experimental results demonstrated that the a crystal growth is not stopped by alloying, but just decelerated, and that lead and bismuth are the most effective at this. The same procedure was then demonstrated successfully on printed circuit boards and hence is shown to be a general method for monitoring a tin growth in critical field applications.

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“…14,15 Taking into account the 26% increase in volume of a-Sn, the theoretical R a is 15 mX. Theoretically then, the experimental resistance should not have exceeded this value.…”

Section: Electrical Resistance Modelmentioning

confidence: 98%

“…The second phase then starts to grow by propagating radially around the seeds. 10,14,15 The inoculator therefore assists in lowering the energy of the system. The experiments performed here used a CdTe inoculator.…”

Section: Introductionmentioning

confidence: 99%

Monitoring the Growth of the α Phase in Tin Alloys by Electrical Resistance Measurements

Maio

Hunt

2009

Journal of Elec Materi

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“…Recent direct observation of tin pest growth in vacuum at À35°C, in seeded bulk tin (99.99%), showed radial growth from the inoculation site. 12 The growth rate varied from different starting sites and appeared to become constant after 5 mm from the origin; typical average values were around 1.7 9 10 À7 m s À1 . With multiple initiation sites, as governed by the seeding process, an entire sample (50 mm 9 2 mm 9 2 mm) was transformed in less than 48 h. Such growth rates are dramatically more rapid than those observed in the present study.…”

Section: Rates Of Tin Pest Formationmentioning

confidence: 96%

Further Observations on Tin Pest Formation in Solder Alloys

Plumbridge

2010

Journal of Elec Materi

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The most recent observations of the response of bulk samples of several commercial solder alloys, exposed to temperatures below the allotropic transition for tin (13°C) for extended periods, are reported. Damage associated with tin pest development has been arbitrarily graded into six levels, and the formation of visible a-phase warts used for comparative purposes. Since the previous examination, some 2 years ago, tin pest has been observed for the first time in the traditional Sn-37Pb solder alloy after exposure at À18°C and À40°C, and actual warts were apparent in as-cast Sn-0.5Cu stored at À40°C and in as-cast Sn-3.5Ag after exposure at À18°C. No tin pest was detected in Sn-Zn-3Bi after exposure for periods up to 6 years. Tin pest continued to develop in those lead-free alloys in which it had previously been observed, indicating the probability that all would eventually disintegrate in time. In general, prior thermal or mechanical treatment accentuated tin pest formation. The influence of exposure temperature was unclear, since some alloys (Sn-0.5Cu and Sn-3.8Ag-0.7Cu) experienced more damage at À18°C, but others (Sn-37Pb and Sn-3.5Ag) were more susceptible at À40°C. From a consideration of the findings and other published information, it is contended that impurity levels below 0.1 mass% (1000 ppm) play a vital role in determining whether tin pest develops in realistic timescales. A major factor in the absence of tin pest, to date, on actual joints may be simply the mismatch between the timescales experienced in service and those in long-duration laboratory tests.

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“…Some studies have also pointed out that the subcooling temperature required for this transition in practical applications is about a dozen degrees lower than 13.2 °C [25]. In general, the low temperature factor can increase the driving force and the free energy difference ΔG [26]. Conversely, the low temperature factor can reduce the thermal energy of the lattice and the atom migration speed [26].…”

Section: Introductionmentioning

confidence: 99%

Microstructure and Grain Orientation Evolution in SnPb/SnAgCu Interconnects Under Electrical Current Stressing at Cryogenic Temperature

En²,

Zhou³

et al. 2019

Materials

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Electromigration was characterized at the cathode Cu/solder interface—without the effect of Joule heating—by employing scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses. Rapid (Cux,Ni1−x)6Sn5 intermetallic compound (IMC) growth was observed at the anomalous region at the cathode end due to the effect of current crowding. The abnormal isotropic diffusion and parallel distribution of Pb were characterized in an ultra-low temperature environment in a monocrystalline structure stressed at −196 °C. The interesting results were attributed to crystallographic transformation due to the simultaneous effect of cryogenic and electrical stressing. The diffusion behavior of Pb atoms in face-centered cubic lattices performed isomorphism. As a result, Pb atoms of the bump gathered at the high-energy grain boundaries by diffusing through the face-centered cubic lattices around the long grain boundary, eventually forming a long-range distribution and accumulation of Pb elements. Our study may provide understanding of cryogenic electromigration evolution of the Cu/solder interface and provide visual data for abnormal lattice transformation at the current stressing.

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Time-lapse photography of the β-Sn/α-Sn allotropic transformation

Cited by 17 publications

References 6 publications

Monitoring the Growth of the α Phase in Tin Alloys by Electrical Resistance Measurements

Monitoring the Growth of the α Phase in Tin Alloys by Electrical Resistance Measurements

Further Observations on Tin Pest Formation in Solder Alloys

Microstructure and Grain Orientation Evolution in SnPb/SnAgCu Interconnects Under Electrical Current Stressing at Cryogenic Temperature

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