Characteristics of Tin Whisker Growth on Matte Tin Surface Finishes by Acceleration Conditions

Purpose The aim of this paper is to present a review of the tin whisker growth phenomena. The study focuses mainly on whisker growth in a corrosive climate when the main inducing factor of the whisker growth is oxidation. The tin whisker phenomenon is still a big challenge in lead-free reflow soldering technology. Modern lead-free alloys and surface finishes with high tin content are considered to be possible sources of whisker development, also the evolution of electronic devices towards further complexity and miniaturization points to an escalation of the reliability risks. Design/methodology/approach The present work was based on a worldwide literature review of the substantial previous works in the past decade, as well as on the results and experience of the authors in this field. Findings The effect of corrosion on tin whisker growth has been under-represented in reports of mainstream research; however, in the past five years, significant results were obtained in the field which raised the corrosion phenomena from being a side effect category into one of the main inducing factors. This paper summarizes the most important findings of this field. Practical implications This literature review provides engineers and researchers with a better understanding of the role of corrosion in tin whisker growth and the current challenges in tin whisker mitigation. Originality/value The unique challenges and future research directions about the tin whisker phenomenon were shown to highlight rarely discussed risks and problems in lead-free soldering reliability.

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The Effects of Nickel Underlayer and Solder Dipping as Tin Whisker Mitigations in Tin Surface Finishes

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.554.47 ◽

2014 ◽

Vol 554 ◽

pp. 47-51

Author(s):

Hooi Peng Lim ◽

Ali Ourdjini ◽

Tuty Asma Abu Bakar

Keyword(s):

Whisker Growth ◽

Hazardous Substances ◽

Lead Free ◽

Bending Test ◽

Tin Whisker ◽

Surface Finishes ◽

Whisker Length ◽

External Stresses ◽

Pure Sn

Driven by environmental concerns and the enforcement of Restriction of Hazardous Substances Directive (RoHS) to ban the use of lead in electronics, the global electronics industry has migrated toward lead-free electronics. However, the adoption of lead-free tin (Sn) surface finish is known to form whiskers. These whiskers grow spontaneously from the Sn finish layer as a stress-relief over time causing device failures. In the present research, whisker growth is investigated via immersion Sn finishes on Cu substrate. The effects of Sn layer thickness, addition of Ni under-layer and solder dipping on whisker growth are investigated by storing the samples under ambient temperature for up to 24 weeks. The effects of external stresses were also studied using bending test. The results showed that whisker length on immersion Sn increases with time for all the samples either with or without Ni under-layer. Thicker Sn coating showed more whisker growth compared with thinner Sn coating. The longest whisker length of 23μm was observed for Sn coating with 2μm thickness. The addition of Ni as under-layer was found to be more effective in mitigating the whisker growth by extending the incubation time for whisker formation. Compared to immersion Sn, solder dipping in pure Sn showed no whisker growth. However, alloying Sn with 0.4%wtCu resulted in whisker growth indicating the role of Cu in promoting whiskers formation.

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