Tin Whiskering

What is it?

Tin whiskers are 'hair-like' protrusions that grow spontaneously, but unpredictably, from an object that has a tin coated surface. They can be anything from sub-micron to ten microns in diameter and may grow to become several millimetres long.

Why does it happen?

It is known that tin whiskers occur in areas where the tin coating is in compressive stress. Growth rates can vary significantly and after being dormant for anything from a few days to several years after plating, it is possible for growth to occur at a rate of several millimetres per year, (although it is typically slower than this).

What problems can it cause?

The main concern over tin whiskers is that they can cause a number of reliability issues and even complete failure. A whisker that bridges two conductors can cause a short circuit, or at least an intermittent surge in power consumption. In the worst cases, a shorting whisker may enable sufficient current to be drawn lead to arcing.

There are concerns that due to the increasing miniaturisation of electronics, tin whiskering will lead to an increasing number of reliability related problems.

How can it be prevented?

Although there has been a large amount of research into factors influencing whisker formation there are still a significant number of questions that need to be answered.

Modern tin plating processes have been developed to minimise the likelihood of whiskering occurring, although most manufacturers still seem unable to guarantee that whiskering will never occur.

By using newer process chemistries together with other approaches such as the deposition of an underlying nickel layer, it is possible to significantly reduce the likelihood of whiskering occurring. Fears over whiskering seem to be receding and it is predicted that tin finishes will become increasingly popular on both components and circuit boards.