Controlled positions and kinetic analysis of spontaneous tin whisker growth

Su, Chien Hao; Chen, Hao; Lee, Hsin Yi; Wu, Albert T.

doi:10.1063/1.3643472

Cited by 18 publications

(8 citation statements)

References 13 publications

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“…There are many factors that can contribute to the stress increase in the Sn finishes, such as IMC formation along grain boundaries [1,2,[4][5][6], CTE mismatch between Sn finish and substrate material during thermal cycling test [7][8][9], oxidation and corrosion [10,11]. It has been widely accepted that the Sn whisker growth is a stress-release phenomenon [1,4,8,10,12] Sn whisker growth mainly depends on the diffusion flow of internal atoms, which is a very slow process and also needs vacancy diffusion.…”

Section: Introductionmentioning

confidence: 99%

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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Section: Introductionmentioning

confidence: 99%

Tin whisker growth on electroplated Sn multilayers

Ding

Gong

2015

J Mater Sci: Mater Electron

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“…They found that whiskers did not grow out of the sites where the oxide was removed. Similarly, Su et al 10 showed that whiskers can grow at the holes in a thick patterned oxide but not all of the holes will develop whiskers. These results indicate that a weak or absent oxide is necessary for whisker growth but is not enough to make whiskers grow.…”

Section: Introductionmentioning

confidence: 91%

Significance of Nucleation Kinetics in Sn Whisker Formation

Chason

Pei

Briant

et al. 2014

Journal of Elec Materi

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Sn whiskers are believed to form in response to stress in layers used as protective coatings. However, what makes them form at specific sites on the surface is not known. We have used thermal expansion mismatch to induce stress and observe the resulting whisker formation. Cross-sectional measurements of the region around whiskers show that there are oblique grain boundaries under the whiskers that are not seen in the as-deposited columnar structure. The kinetics also suggest that the whiskering sites may be formed by a nucleation process. Based on these results, we propose a nucleation mechanism in which the boundaries of the surrounding grains migrate due to strain energy differences and create oblique boundaries at which whiskers can form. A simple model is developed to predict the stress-dependence of the nucleation rate.

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“…Multiple potential underlying factors have been investigated: grain orientation, 7,21 surface defects, 22,23 weak oxide, 8,22,24 IMC pileup, 25,26 and microstructure. 9,11,25,27 Although all may play a role in different systems, the most common feature underlying whiskers/hillocks is that they grow out of grains near the surface.…”

Section: Introductionmentioning

confidence: 99%

Measuring the Stress Dependence of Nucleation and Growth Processes in Sn Whisker Formation

Chason

Pei

2015

JOM

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Sn whiskers/hillocks are believed to form due to stress in the layers, but the dependence on the stress has been difficult to quantify. We therefore used the thermal expansion mismatch between Sn thin films and Si substrates to induce controlled stress by heating. This enables us to measure the average stress in the layer (using wafer curvature) at the same time as we monitor the nucleation rate (using optical microscopy). Scanning electron microscopy of the surface after intervals of heating is also used to quantify the whisker volume as a function of stress and time. The results allow us to determine the dependence of the whisker nucleation rate and the growth rate on the applied stress. They also show that whisker formation is not the dominant mode of plastic strain relaxation in the Sn layer.

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Controlled positions and kinetic analysis of spontaneous tin whisker growth

Cited by 18 publications

References 13 publications

Tin whisker growth on electroplated Sn multilayers

Tin whisker growth on electroplated Sn multilayers

Significance of Nucleation Kinetics in Sn Whisker Formation

Measuring the Stress Dependence of Nucleation and Growth Processes in Sn Whisker Formation

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