Tin whiskers often cause failures in relays, and have been found upon examination of failed relays in nuclear power facilities. Pacemakers have been recalled due to tin whiskers. Research has also identified a particular failure mode for tin whiskers in vacuum (such as in space), where in high-power components a short-circuiting tin whisker is ionized into a plasma that is capable of conducting hundreds of amperes of current, massively increasing the damaging effect of the short circuit. The possible increase in the use of pure tin in electronics due to the RoHS directive drove JEDEC and IPC to release a tin whisker acceptance testing standard and mitigation practices guideline intended to help manufacturers reduce the risk of tin whiskers in lead-free products.
|
|
Diethyl phthalate and diethylhexyl phthalate have been found in e-liquids. Some e-liquids contain tin "whiskers," microscopic crystals that originate from tin in the solder joints.
|
|
Whiskers can be small enough to pass through air filters and can settle inside equipment, resulting in short circuits and system failure. Tin whiskers don't have to be airborne to damage equipment, as they are typically already growing in an environment where they can produce short circuits. At frequencies above 6 GHz or in fast digital circuits, tin whiskers can act like miniature antennas, affecting the circuit impedance and causing reflections. In computer disk drives they can break off and cause head crashes or bearing failures.
|
|
Replacing lead has many problems, including a higher melting point, and the formation of tin whiskers causing electrical problems. Tin pest can occur in lead-free solders, leading to loss of the soldered joint. Replacement alloys are rapidly being found, although problems of joint integrity remain.
|
|
For example, tin whiskers were responsible for a 5% failure rate in certain components of Swiss Swatch watches in 2006, prior to the July implementation of RoHS, reportedly triggering a US$1 billion recall. Swatch responded to this by applying for an exemption to RoHS compliance, but this was denied.
|
|
When closed, these then show unacceptably high resistance; they may also migrate and cause shorts. Tin whiskers can form on tin-coated metals like the internal side of the packagings; loose whiskers then can cause intermittent short circuits inside the packaging. Cables, in addition to the methods described above, may fail by fraying and fire damage.
|
|
Tin finishes are the most popular of lead-free finishes. Nevertheless, this brings up the issue of how to deal with tin whiskers. The current movement brings the electronics industry back to the problems solved in the 1960s by adding lead. JEDEC has created a classification system to help lead-free electronic manufacturers decide what provisions to take against whiskers, depending upon their application.
|
|
Potential reliability concerns were addressed in Annex item #7 of the RoHS directive, granting some specific exemptions from regulation until 2010. These issues were raised when the directive was first implemented in 2003 and reliability effects were less known. Another potential problem that some lead-free, high tin-based solders may face is the growth of tin whiskers. These thin strands of tin can grow and make contact with an adjacent trace, developing a short circuit.
|
|
Historically tin whiskers have been associated with a handful of failures, including a nuclear power plant shutdown and pacemaker incident where pure tin plating was used. However, these failures pre-date RoHS. They also do not involve consumer electronics, and therefore may employ RoHS-restricted substances if desired. To help mitigate potential problems, lead-free manufacturers are using a variety of approaches such as tin-zinc formulations that produce non-conducting whiskers or formulations that reduce growth, although they do not halt growth completely in all circumstances.
|
|
Silver whiskers growing out of surface-mount resistors Metal whiskering is a phenomenon which occurs in electrical devices when metals form long whisker- like projections over time. Tin whiskers were noticed and documented in the vacuum tube era of electronics early in the 20th century in equipment that used pure, or almost pure, tin solder in their production. It was noticed that small metal hairs or tendrils grew between metal solder pads causing short circuits. Metal whiskers form in the presence of compressive stress.
|
|
The 2006, European, RoHS regulations prompted the research needed to move from traditional lead-based solder connection processes to a more environmentally friendly approach. Much manufacturing is currently being done with tin-based solder to address this issue. Using tin requires much higher reflow temperatures and can result in rework stages due to electric shorts caused by tin-whiskers (electrically conductive structures formed in this process) and other issues in the manufacturing process which are avoided by the Occam process. PCB’s themselves are usually created by use of a phenolic resin, itself a corrosive, toxic substance completely removed from the Occam process.
|
|
Galaxy IV was a telecommunications satellite that was disabled and lost due to short circuits caused by tin whiskers in 1998. It was initially thought that space weather contributed to the failure, but later it was discovered that a conformal coating had been misapplied, allowing whiskers formed in the pure tin plating to find their way through a missing coating area, causing a failure of the main control computer. The manufacturer, Hughes, has moved to nickel plating, rather than tin, to reduce the risk of whisker growth. The trade-off has been an increase in weight, adding per payload.
|
|
Thus, unit testing would result in certifying the safety of a product which has unsafe components that could be swallowed by a child. Other manufacturers point out the problem of defining "children's products."CPSC Public Hearing on Lead Standards , 6 November 2008, (accessed 1 December 2008) Electronic products such as video games could be considered children's products, and are therefore subject to that testing. Electronics products contain lead as a component of solder; whereas the European Restriction of Hazardous Substances Directive standards have long attempted to phase out lead solder, the tin solder is known to suffer from a defect known as tin whiskers.
|
|