Corrosion-induced tin whisker growth in electronic devices: a review

Abstract

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.

In Situ Reconstruction of a Hierarchical Sn‐Cu/SnOxCore/Shell Catalyst for High‐Performance CO2Electroreduction

“…However, once the used catalysts are examined by ex situ HRTEM and contact with air, the surface Sn species of catalysts will be instantly oxidized in air and combine with the SnO x matrix to form SnO 2 /SnO x (Figure f) . The crystalline Sn are prone to form the SnO 2 crystals with a spontaneous oxidation in air, which is similar to the surface oxidation of crystalline Sn in the pure Sn catalyst (Supporting Information, Figure S5) and also in accordance with previous reports . Furthermore, ex situ XRD and SEM results suggest no evident variation for the integral structure and morphology of Sn 2.7 Cu catalyst after CO 2 RR stability measurement (Supporting Information, Figures S13 and S14), indicating that the Sn 2.7 Cu catalyst is stable during the CO 2 RR process.…”

“…However, the geometrical total current densities of both Sn (Figure a) and SnCu 1.1 (Figure e) catalysts obviously decay lower than 50.0 mA cm −2 and their C 1 Faradaic efficiency drop below 89.0 % even within 10 h, indicating that both Sn and SnCu 1.1 catalysts cannot provide a stable CO 2 RR performance. Ex situ HRTEM images display that the Sn catalyst still has many SnO 2 crystals on its surface because of spontaneous oxidation in air (Figure b; Supporting Information, Figure S18), while the SnCu 1.1 catalyst maintains its core–shell structure with the homogeneous Sn‐Cu alloy core and a tiny shrinkage of amorphous SnO x shell from 2.0 nm (Supporting Information, Figure S6) to 1.8 nm (Figure f; Supporting Information, Figure S21) after CO 2 RR stability test. Notably, the SnO x shell in Sn 2.7 Cu catalyst can be in situ reconstructed owing to its hierarchically heterogeneous Sn‐Cu alloy/Sn core structure under the cathodic potentials of CO 2 RR (Supporting Information, Figure S20), but the in situ reconstructed Sn/SnO x interface tends to be immediately oxidized to SnO 2 /SnO x after exposure to air for ex situ tests (Figure d; Supporting Information, Figure S19) .…”

Overview of Selected Issues Related to Soldering

“…• Temperature and humidity [30] Due to their size and growth on shiny surfaces, whiskers are very difficult to detect by classical optical methods. The experimental results of whisker growth are unpredictable and unrepeatable, and so far the exact mechanism of their growth is not known.…”

Atomic layer deposition (ALD) for environmental protection and whisker mitigation of electronic assemblies

“…An overall consensus on factors playing a fundamental role in whisker growth has been reached: (i) in-plane compressive stresses, caused by volumetric expansion following the Sn-Cu intermetallic growth, providing the driving force for whiskers to grow [9], (ii) rapid grain boundary self-diffusion from the tin electroplate interior to the growing whisker [10], and (iii) a surface oxide layer which limits surface vacancy sources, thus preventing diffusion and corresponding stress relief via diffusional processes [11]. In addition, several other factors have shown to influence whisker growth such as morphology and crystallographic structure of the intermetallic compound [12], mismatch in the coefficients of thermal expansion (CTE) causing stress during thermal cycling [13], elevated temperatures and high humidity conditions leading to corrosion [14], and applied external mechanical stress [15]. It is also here important to recall that morphologies and physical properties of the Sn layers such as thickness, grain size, and crystallographic structure [13], as well as other factors such as current load [16,17] and electrostatic forces [18], also contribute to whisker formation.…”