Tin Whiskers vs. Metal Dendrites: What’s the Difference?

10 Nov Tin Whiskers vs. Metal Dendrites: What’s the Difference?

Tin whiskers and metal dendrites are structural formations that appear in tin materials during manufacturing and finishing processes. While metal dendrites have been a long-identified metal fabrication problem, the discovery of tin whiskers came more recently. The two seem similar to the untrained eye, making it difficult to tell the difference between the two structural defects.

To correctly identify tin whiskers vs. metal dendrites, technicians must understand the phenomenon and the best practices for mitigating tin whisker formation. The ability to recognize metal dendrites and tin whiskers is critical during testing and inspection processes.

Tin Whiskers: What are They and How Do They Form?

At their core, tin whiskers are crystalline structural formations that can occur in pure tin and other pure metals like zinc, cadmium, and silver. The structures can grow to several millimeters long but rarely extend beyond 10 mm. Manufacturers and inspectors primarily find tin whiskers in tin plating, especially during the final finish of a manufactured component or after electroplating.

The crystalline structure of tin whiskers makes them more conductive than the surrounding tin or other metal materials. This varying conductivity increases the risk of electricity traveling from one circuit to another with differing electrical potential, thereby short-circuiting the entire component. This variable conductivity can be problematic, especially in devices with numerous closely placed circuits. Documented issues scale in severity from short circuits up to complete electronic system failure.

Investigations have identified factors that may increase the formation of twin whiskers and elements that do not impact formation. For example, tin whiskers can form whether or not there is an electromagnetic field present. The dissolution of the metal before plating does not affect the likelihood of formation. These strategies may help to reduce the risk of tin whisker formation:

1. When possible, use a tin-lead alloy or another alloy instead of pure tin or zinc.
2. Ensure that tin-plated parts are sufficiently solder-dipped in tin-lead solder.
3. Consider replating areas of a component or product that are particularly likely to develop tin whiskers.
4. Minimize mechanical and physical stress during handling and assembly, as well as during use in the field.

Metal Dendrites: What are They and How Do They Form?

Metal dendrites have a different shape than tin whiskers. They have a tree-like (dendrite-like) structure of crystalline branches that spread throughout the affected metal. They develop along a surface two-dimensionally rather than growing.

These metal dendrites typically appear as molten metal starts to cool and harden. The temperature of the environment the metal rests in as it cools, and the resulting rate of cooling will determine the level of dendrite formation. As such, metal fabricators must find the ideal cooling conditions for each metal and alloy they work with, so the finished products have minimal dendrite formation risk.

Much like tin whiskers, metal dendrites play a role in the metal’s conductivity by altering its chemical, electrical, and mechanical properties. For example, dendrites can change the weldability of the cooled metal and impact the welding method used.

Though creating the proper temperature and cooling conditions for molten metal will reduce the risk of metal dendrite formation, it’s still essential for manufacturers to test cooled metal workpieces for metal dendrites. This process can reduce wasted labor and materials on flawed pieces. Even more importantly, testing helps manufacturers establish ideal conditions as they refine their fabrication process. Using clean printed circuit boards (PCBs), testing for conformal coats on assemblies, and suing UV bumps can also improve the product’s integrity and eliminate the risk of metal dendrite formation.

Tinning Services From SemiPack Services

Tin whiskers and metal dendrites can negatively impact the quality of metal products and increase the risk of electronics failures. It’s important to distinguish between the two to identify risks, resolve issues, and ensure product quality remains high.

At SemiPack Services, we specialize in creating high-quality products that can be made whisker-resistant. We use tin-lead plating because it protects against tin whisker formation better than pure tin and tin alloys with silver. We also provide XRF testing and inspections to examine the metal’s material composition.

Contact us today to see how our whisker-resistant solutions can support your project.