A “tin whisker” is a single crystal of tin that grows spontaneously from the plated surface. Manufacturers who prefer the use of tin over lead plating can encounter problems with their interconnections. As “tin whiskers” grow, they can cause electrical shorts, and/or can flake off, causing physical damage.
Full Answer
What are tin whiskers used for?
A Major Concern For The Electronics Industry These thin strands can break away from the base material and cause problems such as electrical shorts and arcing in all types of electronic components. Tin whiskers are one of the more prevalent types of whiskers because of tin's use in electronic components and circuit boards.
What are Tain whiskers?
Tin whiskers are metal filaments which grow from tin. They are extremely thin, 1-2uM typically, and grow as straight, kinked, or spiraled single crystals of tin.
Can tin whiskers cause electronic circuit problems?
The ability of tin whiskers to cause electronic circuit problems was established in 1951. Many sudden failures and intermittent problems were associated with tin whiskers because of their ability to short closely spaced electronic circuits.
Do tin whiskers still grow?
Tin whiskers will still grow. In fact, many metals, including zinc, cadmium, indium, silver, aluminum, gold, and yes, even lead, grow whiskers.
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 prevent tin whiskers?
Testing is the key to preventing tin whiskers. Testing for material composition and/or material structure should be part of any critical device manufacturing. Testing must be performed independent of the vendor.
Are tin whiskers still a problem?
Although some experimenters have reported whisker growth from tin-lead alloys, such whiskers have also been reported to be dramatically smaller than those from pure tin plated surfaces and are believed to sufficiently small so as not to pose a significant risk for the geometries of today's microelectronics.
What is whisker formation?
Abstract. The filamentary growths of single crystals on material surfaces are termed whiskers. They are seen to nucleate and grow on certain electronic materials either from vapour and liquid phases or by a process induced by residual stresses in electroplated surfaces.
How long does it take for tin whiskers to form?
They can grow fairly rapidly; incubation can range from days to years, according to the NASA backgrounder on whiskers. ¹ There is no set timetable for when they commence growing. A scanning electronic microscope (SEM) photograph of a needle-like tin whisker is shown in Figure 1.
What is tin whisker growth?
Tin whiskers are electrically conductive, crystalline structures of tin that sometimes grow from surfaces where tin (especially electroplated tin) is used as a final finish. Tin whiskers have been observed to grow to lengths of several millimeters (mm) and in rare instances to lengths in excess of 10 mm.
At what temperature does tin disintegrate?
The allotropic transformation At 13.2 degrees Celsius (about 56 degrees Fahrenheit) and below, pure tin transforms from the (silvery, ductile) allotrope of β-modification white tin to brittle, α-modification grey tin. Eventually it decomposes into powder, hence the name tin pest.
What is whisker test?
Tin whisker testing is one way to determine the product's susceptibility to growing whiskers or if any mitigation strategy is successful. Samples are subjected to three main environmental exposures for a specified period.
What are tin whiskers and why are they a hazard to space travel?
This may resemble an alien landscape, but it is actually a microscopic view of tin used to solder electronic components. The long shard rising from the surface is a 'tin whisker' – a spontaneous outgrowth representing a clear and present danger to space missions.
What is whisker wash?
You Sit; We'll Roll Over. We operate in a self-contained luxury mobile grooming unit. Your pet receives one on one care and attention during the entire groom. Our top priority is your pets safety and comfort.
What are whiskers on humans?
Whiskers are vibrissae, keratin filaments that grow out of different follicles than hair. Whisker follicles are much deeper than hair follicles and are surrounded by pockets of blood that amplify vibrations to better communicate information to the nerve cells beside the follicles.
Does lead free solder cause tin whiskers?
It has been proven time and again that in cases where tin whiskers have formed, it is almost never a result of the Pb-free solder, but rather the pure tin-plated surface finish.
Does lead free solder cause tin whiskers?
It has been proven time and again that in cases where tin whiskers have formed, it is almost never a result of the Pb-free solder, but rather the pure tin-plated surface finish.
What is whisker in jeans?
Whiskers (also known as 'moustaches' or 'hige') are fades on the thighs of jeans. They are relatively thin diagonal or horizontal creases that form as you wear your jeans. If your jeans are made from raw denim, you will create the whiskers as you wear in the jeans.
What is tin whiskering?
Recently, a little-known phenomenon called tin whiskering caused the recall of several models of a pacemaker. This incident revealed tin whiskers to be a general threat to all users and manufacturers of medical devices that incorporate electronic circuitry. To prevent future problems, field personnel will need to educate themselves ...
How long is a tin whisker?
They can reach a length of 9mm (3/8") and carry 10mA of current before burning up. The electrical resistance of a tin whisker 3mm (1/8") long is about 50 ohms.
What would have prevented tin whisker growth?
Examination of the manufacturing process revealed that the manufacturer's specification for the crystal component should have prevented tin-whisker growth. The crystal component specification called for gold, nickel, or solder plating. Any one of these case coatings would have prevented the tin whisker problem.
Why are whiskers dangerous?
Because of their current carrying ability and low electrical resistance, whiskers are a threat to electronic circuits. The ability of tin whiskers to cause electronic circuit problems was established in 1951.
How can investigators help prevent tin whiskers?
The investigator can help prevent tin whisker problems by enquiring into material testing of critical electronic components. However, knowledge of tin whiskers is new in the industry. The investigator may first have to educate manufacturers about tin whisker problems before looking into material testing.
How to control whisker growth?
The most common is to avoid using tin. Other metals or alloys of tin are used instead with solder (tin/lead) being the most popular. The other method is known as "reflow." After the tin is in place, the tin coated part is heated to a temperature above tin's melting point. This heating releases any stress that exists within the tin deposit.
What is reflow tin?
Other metals or alloys of tin are used instead with solder (tin/lead) being the most popular. The other method is known as "reflow.". After the tin is in place, the tin coated part is heated to a temperature above tin's melting point. This heating releases any stress that exists within the tin deposit.
What are tin whiskers?
Tin whiskers are electrically conductive, single crystal eruptions that can grow from surfaces where tin is deposited on a substrate surface (Fig. 1). High aspect ratio Sn whiskers are typically 1-5 µm in diameter and between 1-500 µm in length. They present reliability problems for the electronics industry with ongoing reports of tin whisker induced failures, particularly in the satellite and defense sectors (Fig. 2). Further, the current worldwide initiative to reduce the use of lead (Pb) is driving the electronics industry to consider high tin alternatives to the widely used Sn-37Pb alloys used for plating and solder. Continuing reports of tin whisker induced failures coupled with the lack of an industry-accepted understanding of tin whisker growth and/or test methods to identify whisker-prone products has made blanket acceptance of pure tin plating a risky proposition for high reliability systems. Harsh environments may exacerbate the problem by causing thermal and/or mechanical stresses in tin coated surfaces, leading to the growth of tin whiskers and to tin whisker induced failures. A common failure mode for whisker-prone electronic systems is whisker bridging, which causes electrical shorts (Fig. 3-4).
What is the role of humidity in whisker production?
Currently, we are investigating the role of calibrated, controlled humidity on whisker production and the role of electric fields in the whiskering process. Humidity is important due to the preponderance of studies which report enhanced whisker growth in the presence of oxygen. Further, in the cracked oxide theory of whisker growth, sufficient compressive stress is presumed to occur at positions of oxide weakness which are the locations of whisker emission. A unique viewpoint of the whisker surface oxide is afforded by in-situ, real-time scanning electron microscopy (SEM) observations of Sn whiskers during heating to temperatures greater than the melting point of Sn. As the Sn melts, the whiskers buckle, curl, and drain of liquid Sn, leaving behind a thin, solid, emptied tube of tin oxide with its higher melting point. With further electron-beam heating, the tin oxide tube frequently forms a coagulated spherical ball of material which is the final resting place of the dead whisker skeleton.
Is tin whisker growth mechanical?
While tin whisker growth is believed to be largely mechanical, there is currently no general agreement on the mechanism governing the growth of tin whiskers.
What causes whiskers in tin?
Stresses can come from many places and are accepted in the lead world, but these same stresses seem to induce whiskers in the pure tin world. Sources of stress include compressive forces from external activity like tightening a fastener; bending or stretching that might occur in the formation of the leads; and even nicks or scratches created in normal handling. Finally, a seemingly mundane difference in the coefficient of thermal expansion between the lead-frame base material and the tin-plating material has been cited as a possible source for stress that causes the whisker problem. 1 Annealed matte tin seems to be the most successful finish for reducing stress and thus is often used by component companies as a lead-free finish. 3
How thin are tin whiskers?
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.
What happens when a whisker is between two conductors?
When a whisker grows between two conductors, the whisker usually fuses (disappears), creating a momentary short circuit. In some cases the whisker forms a conductive path, creating false signals at an incorrect location which can, in turn, cause improper operation of the device in question. In very rare cases, rather than disappearing like a fuse link, the whisker can instead form a conductive plasma capable of carrying over 200 A. Whiskers can also break and fall into contact with printed circuit board (PCB) traces and other conductive pieces where they interfere with electrical signals. In optical systems they can disrupt or diminish the transmitted light; in MEMS they can interfere with the intended mechanical function.
Do satellites grow whiskers?
Finally, satellites grow whiskers very rapidly. Recall that the higher the altitude, the more rapid the whisker formation. Consequently, the various satellite agencies now require a minimum of 3% ead in the finish of the leads. Most IC makers actually supply a more conventional 85/15 SnPb finish.
Can whiskers break a fuse?
In very rare cases, rather than disappearing like a fuse link, the whisker can instead form a conductive plasma capable of carrying over 200 A. Whiskers can also break and fall into contact with printed circuit board (PCB) traces and other conductive pieces where they interfere with electrical signals.
Is whisker real?
Whiskers are real and they cause real problems, but they are also random. How big an issue are they really?
Is the Tin Whisker issue insurmountable?
Both the RoHS directive and the tin-whisker issue present challenges, but they are not insurmountable. With proper choice of solder, manufacturers of high-reliability devices can achieve RoHS compliance while still maintaining reliability, performance, and cost objectives.