Formation and Hazards of Tin Whiskers
🔬 The Invisible Killer in the Microscopic World · Electronic Reliability Analysis
I. Formation of Tin Whiskers
Tin whiskers are whisker-like pure tin crystals that naturally grow from tin or tin-plated metal surfaces. Their formation process involves the physical displacement of metal crystals, usually caused by stress after welding.
The growth of tin whiskers is a room-temperature creep behavior under stress gradients, requiring three conditions: stress source, oxide layer constraint, and long-range diffusion of Sn atoms. The driving force for whisker growth is mainly internal stress, such as the compressive stress generated on the tin layer by the intermetallic compound Cu6Sn5 formed at the Cu/Sn interface.
II. Formation Mechanism
The growth mechanism of tin whiskers is not yet fully understood, but studies show that compressive stress inside the plating layer is the main driving force for whisker growth. Specifically, diffusion between tin and copper forms intermetallic compounds (IMC). This process rapidly increases internal stress in the tin layer, prompting tin atoms to diffuse along grain boundaries, thereby producing tin whiskers. Sources of compressive stress can be mechanical, thermal, or chemical.
III. Influencing Factors
Controlling the following factors can accelerate or inhibit tin whisker growth:
Covers material properties of the coating and substrate (such as thermal expansion coefficient, atomic diffusion capability, ability to react to form IMC), as well as coating alloy, thickness, crystal structure, and surface condition.
Includes external mechanical stress, temperature, humidity, ambient atmosphere, external air pressure, and radiation.
IV. Hazards of Tin Whiskers
The presence of tin whiskers can negatively impact the performance and reliability of electronic products. Their hazards mainly include:
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⚡ Permanent Short Circuit
After growing to a certain length, tin whiskers may short two different conductors. Especially in low-voltage, high-impedance circuits, they may produce stable and lasting short circuits. -
💥 Transient Short Circuit
Under high voltage, the current may exceed what the whisker can withstand, causing it to fuse and producing a transient short circuit. -
📶 Signal Interference
The presence of tin whiskers may alter signal paths, causing signal interference and affecting the normal function of electronic devices. -
🔥 Insulation Breakdown and Heat Accumulation
May penetrate insulating materials, leading to insulation breakdown and circuit failure; short circuits may cause local heat accumulation, increasing fire risk. -
🌍 Environmental Pollution
The formation and shedding of tin whiskers may pollute the environment, especially in the production of lead-free electronic products where tin whisker issues are more prominent.
Conclusion
The formation of tin whiskers is a complex physicochemical process influenced by multiple factors. Its hazards to electronic products cannot be ignored, potentially leading to short circuits, signal interference, insulation breakdown, and other issues.
Therefore, controlling and preventing tin whisker formation is particularly important in electronics manufacturing. Through reasonable material selection, process optimization, and strict reliability testing, risks from tin whiskers can be effectively reduced, improving the reliability and stability of electronic products.
