Thermal stress driven Sn whisker growth: in air and in vacuum

Jo, Jung-Lae; Nagao, Shijo; Sugahara, Tohru; Tsujimoto, Masanobu; Suganuma, Katsuaki

doi:10.1007/s10854-013-1336-6

Cited by 2 publications

(1 citation statement)

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“…Particularly in thermal cycling, the refined grain structure suppressed surface oxidation cracking along grain boundaries, which is relevant to reduce whisker density. 20 It is remarkable that the obvious whisker mitigation effect starts from 0.5 wt.% of Bi addition even in thin plating films of 5 lm thickness.…”

Section: The Whisker Mitigation Mechanism By Least Bi Additionmentioning

confidence: 98%

Mitigation of Sn Whisker Growth by Small Bi Additions

Nagao

Hamasaki

et al. 2013

Journal of Elec Materi

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In this study, the morphological development of electroplated matte Sn and Sn-xBi (x = 0.5 wt.%, 1.0 wt.%, 2.0 wt.%) film surfaces was investigated under diverse testing conditions: 1-year room-temperature storage, high temperature and humidity (HTH), mechanical loading by indentation, and thermal cycling. These small Bi additions prevented Sn whisker formation; no whisker growth was observed on any Sn-xBi surface during either the room-temperature storage or HTH testing. In the indentation loading and thermal cycling tests, short (<5 lm) surface extrusions were occasionally observed, but only on x = 0.5 wt.% and 1.0 wt.% plated samples. In all test cases, Sn-2Bi plated samples exhibited excellent whisker mitigation, while pure Sn samples always generated many whiskers on the surface. We confirmed that the addition of Bi into Sn refined the grain size of the as-plated films and altered the columnar structure to form equiaxed grains. The storage conditions allowed the formation of intermetallic compounds between the plated layer and the substrate regardless of the Bi addition. However, the growth patterns became more uniform with increasing amounts of Bi. These microstructural improvements with Bi addition effectively released the internal stress from Sn plating, thus mitigating whisker formation on the surface under various environments.

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Section: The Whisker Mitigation Mechanism By Least Bi Additionmentioning

confidence: 98%