What is meant by tin whiskers?
Tin whiskers (also called Sn whiskers or metal whiskers) are microscopic, conductive, hair-like crystals that emanate spontaneously from pure tin (especially electroplated tin) surfaces. Whiskers form primarily on elemental metals, but have also been found on alloys.
How do you mitigate tin whiskers?
- Avoid Tin Plated Parts.
- Strip and Replate.
- Solder Dip the Plated Surfaces Sufficiently Using a Tin-Lead Solder.
- Select a Matte or Low Stress Tin Finish.
- Select Underplating (Barrier layer) to Reduce Intermetallic Formation.
- Vary Thickness of Tin Plating.
- Reflow Of Pure Tin Plated Surfaces.
What causes tin whisker growth?
The exact cause of tin whisker growth is still not fully understood. It is known that a whisker grows from its base and that the tin around the base does not thin as the whisker grows. It seems that the energy for growth comes from microstrains present in the tin or from externally applied pressure.
Are tin whiskers still a problem?
An Overview of the Problem Tin whiskers are real. They are microscopic conductive fibers emanating from pure tin surfaces, and they pose a serious problem to electronics of all types. Tin whiskers are not a new phenomenon resulting from the switch to lead-free electronics.
What causes metal whiskers?
Metal whiskers form in the presence of compressive stress. Zinc, cadmium, and even lead whiskers have been documented. Many techniques are used to mitigate the problem including changes to the annealing process (heating and cooling), addition of elements like copper and nickel, and the inclusion of conformal coatings.
What is whisker material?
A whisker is a thin strand of metal that grows out of the original shape of the metal. A whisker can form only on some metals and metal alloys. It is thought that whiskers are created by residual stresses in the metal; however, the exact mechanism that causes whisker formation is not well understood.
How long does it take for tin whiskers to grow?
Tin whiskers are almost invisible to the human eye and are 10 to 100 times thinner than a human hair (see figure 1). They can bridge fairly large distances between electrical device leads, and in so doing, can short out the conductors. They can grow fairly rapidly; incubation can range from days to years.
Does lead free solder cause tin whiskers?
Pb-free solders are almost always alloys of tin, silver, copper and/or antimony; never pure tin. During the initial Pb-free transisiton, the number of cited tin whisker cases grew because the Pb-free solder alloys stress a tin plating more than leaded solder, so whiskers were more likely to occur.
Does conformal coating prevent tin whiskers?
After more than two years of experimentation, we have found that conformal coat does not prevent tin whisker formation although it does appear to substantially reduce the rate of growth.
How long does it take for tin whiskers to form?
What whiskers are for?
The primary function of whiskers is to aid with vision, especially in the dark, by providing additional sensory information — much like antennae on other creatures. Although it’s often called “tactile hair,” the whisker itself cannot feel anything.
What type of solder is prone to tin whiskers?