4 Tips for Preventing Tin Whiskers

4 Tips for Preventing Tin Whiskers

Tin plating—i.e., a process that involves coating a substrate with layers of tin—is commonly used during the manufacture of printed circuit boards (PCBs). It is used to protect the copper traces from corrosion, oxidation, and other possible forms of degradation during production and use.

As tin is readily available, easily solderable, and highly corrosion-resistant, it serves as an effectual and cost-effective plating alternative to more expensive materials such as gold, palladium, and platinum. Unfortunately, it carries the risk of tin whiskers, which are crystalline structures that sometimes form on tin-finished surfaces. The structures can grow to lengths up to and exceeding 10 millimeters. As they are electrically conductive, they can cause nearby circuit elements to connect, which can lead to short-circuiting and, consequently, damage to the electrical or electronic system.

Industry professionals have developed and discovered many ways to reduce the risk of the structures forming on tin-plated surfaces. The following article discusses four of them.

1. Avoid Using Pure Tin or Zinc

Most industry professionals consider pure tin as the most susceptible to whisker formation. However, the crystalline structures can also grow in other materials, including cadmium, silver, and zinc. Using an alloy (e.g., tin-lead) for the plating operation helps reduce the risk of whiskers forming.

2. Test for Material Composition and/or Structure

In critical devices, the material composition and structure can significantly affect performance, with the right composition and structure leading to good performance and the wrong composition and structure leading to bad performance. Before a component is integrated into such an assembly, the manufacturer should test it to ensure it has the right composition and structure. This is especially important for electric and electronic devices as a component that incorrectly has tin plating may be susceptible to short-circuiting.

One of the most commonly used testing methods is X-ray fluorescence (XRF) testing.

3. Minimize Stress

Most material experts agree that stress is a catalyst for tin whisker formation. The material deposition process creates the initial stress, while interactions between the plated layer and the underlying substrate further exacerbate it. Eventually, the stress reaches a point where it forces some of the tin atoms outward. By subjecting the plated surface to stress-relieving treatments, industry professionals can release any stress in the layer and, consequently, reduce the risk of tin whiskers forming.

One of the most common methods of stress relieving tinned surfaces is solder dipping them in tin-lead solder. This process heats the material to above its melting point, allowing it to reflow and release stress.

4. Replate the Susceptible Surface Areas

In late manufacturing stages or after component delivery, some manufacturers choose to prevent tin whiskers from forming by replating the whisker-prone areas. They can either strip the pure tin plating from the area and replace it with a less susceptible material or plate over the existing layer. However, the latter option carries a risk of whiskers forming from the pure tin layer through the external layer.

Tinning Services From SemiPack Services

At SemiPack Services, we provide electronic manufacturing support services to the high-mix low-volume (HMLV) customers in the semiconductor industry. One of our core service offerings is tinning. We ensure our tinned components fully comply with the customer’s specifications and standards with the following:

  • Fully automated tinning systems to ensure accuracy and precision
  • Tin-lead plating solutions to mitigate the risk of tin whisker formation
  • X-ray fluorescence equipment to determine and verify the composition of materials

To learn more about our tin plating capabilities or discuss your application requirements with one of our representatives, contact us today.

 

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