Least lead addition to mitigate tin whisker for ambient storage

Jo, Jung-Lae; Kim, Keun Soo; Sugahara, Tohru; Nagao, Shijo; Hamasaki, Kyoko; Tsujimoto, Masanobu; Suganuma, Katsuaki

doi:10.1007/s10854-013-1218-y

Cited by 19 publications

(14 citation statements)

References 10 publications

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“…These results are similar to our previous results, where we attempted to eliminate Sn whiskers during 1-year ambient storage by small Pb addition to Sn. 11 The present results confirm that addition of a trace amount of Bi, namely 0.5 wt.% in a 5-lm plated film, is sufficient to mitigate Sn whisker formation for up to 1 year of ambient-temperature storage. Figure 3 shows that the HTH test results exhibit tendencies similar to the ambient storage results.…”

Section: Methodssupporting

confidence: 79%

“…A similar effect caused by alloying Sn-Pb has been reported. 11,13,14 As shown in Fig. 2b, Sn whiskers can be observed only on the pure Sn surface during 1-year ambient storage.…”

Section: Methodsmentioning

confidence: 85%

“…Usually, Sn whiskers grow on a pure Sn surface within 24 h of electroplating. 11 However, in contrast, no whiskers were observed on the Sn-xBi surfaces, regardless of the Bi content, while only hillocks were observed on the Sn-0.5Bi and Sn-1Bi surfaces. These results are similar to our previous results, where we attempted to eliminate Sn whiskers during 1-year ambient storage by small Pb addition to Sn.…”

Section: Methodsmentioning

confidence: 89%

“…11 Addition of even 1 wt.% Pb effectively suppressed Sn whiskers by inhibiting grain boundary (GB) IMC growth without altering the columnar grain structure.…”

Section: Introductionmentioning

confidence: 99%

“…11 When alloying Bi with Sn, the columnar grains of the films changed to equiaxed grains. 12 Under thermal cycling, the measured stress of 7.5-lm Sn with 2.5 wt.% to 10 wt.% Bi content showed relaxation similar to that of Sn-Pb plated samples.…”

Section: Introductionmentioning

confidence: 99%

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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: Methodssupporting

confidence: 79%

“…A similar effect caused by alloying Sn-Pb has been reported. 11,13,14 As shown in Fig. 2b, Sn whiskers can be observed only on the pure Sn surface during 1-year ambient storage.…”

Section: Methodsmentioning

confidence: 85%

Section: Methodsmentioning

confidence: 89%

“…11 Addition of even 1 wt.% Pb effectively suppressed Sn whiskers by inhibiting grain boundary (GB) IMC growth without altering the columnar grain structure.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mitigation of Sn Whisker Growth by Small Bi Additions

Nagao

Hamasaki

et al. 2013

Journal of Elec Materi

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

Nagao

Sugahara

et al. 2013

J Mater Sci: Mater Electron

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Tin whisker growth on electroplated Sn multilayers

Ding

Gong

2015

J Mater Sci: Mater Electron

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As one of the key reliability issues, tin whisker problem has perturbed the electronics industry for several decades. Developing an effective way to mitigate the growth of tin whiskers is of great importance. In this study, we develop a novel multilayer method through alternately plating bright Sn and matte Sn layers to control the tin whisker growth. The samples of bilayer, trilayer and quadlayer were fabricated and stored at 55°C/85 % relative humidity and room temperature to evaluate the whisker growth. Experimental results revealed that the tin whiskers tended to grow on the bilayer and trilayer samples with bright Sn as the top layer. The whiskers originated from the middle or bottom layer and broke through the top layer. Compared to the bottom layer of matte Sn, bright Sn as the bottom layer was prone to promote whisker growth, due to irregular formation of intermetallic compound. With increase of the number of Sn layers, the grain structure of bottom layer became the main factor to affect Sn whisker growth. Uniform thickness of individual Sn layers could help to reduce whisker density. Optimal Sn multilayers are obtained to be matte/bright/matte Sn and bright/matte/ bright/matte Sn with uniform thickness of individual layers.

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Least lead addition to mitigate tin whisker for ambient storage

Cited by 19 publications

References 10 publications

Mitigation of Sn Whisker Growth by Small Bi Additions

Mitigation of Sn Whisker Growth by Small Bi Additions

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

Tin whisker growth on electroplated Sn multilayers

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