Electronic Source Book

Will electronic equipment fail from tin-whisker shorts? (February 9, 2005)

As component suppliers rush to produce lead-free parts in advance of the July 1, 2006 European Union deadline for green products, there may be a serious problem hidden in the parts that are soldered with tin-only instead of tin with traces of lead. The problem is, tin can grow tiny whiskers that can touch other pieces of metal inside an electronic device. Those whiskers can cause a short circuit and ultimately a device failure. In 1998, the $250 million Galaxy 4 communications satellite shut down. Engineers believe the cause was tin whiskers that caused a short circuit and the ultimate failure of the satellite.

Lead-free laws such as The Restriction of Hazardous Materials (RoHS) passed by the European Union in 2002, ban the sale of products containing lead. RoHS goes into effect on July 1, 2006, but in order to make that deadline, the electronics industry is already moving now to products that use tin soldering without the 2 or 3 percent lead content which has proven over 50 years to dampen the whiskering phenomenon. RoHS applies to all electronic products except those produced by the military and portions of the telecommunications industry. The military is exempt from RoHS and the telecommunications industry will have until 2010 to become RoHS compliant.

As the electronics industry rushes to tin-only components, engineers are beginning to voice concerns about the whiskering effect of pure tin. No definitive explanation has been given for the whiskering, though it is known to be mitigated by the presence of small amounts of lead, gold, antimony or indium. Gold has been cited as the most successful additive besides lead in controlling whiskering, but it also adds to the cost of the components, so it has not been used widely. For the most part, compliant components use only tin. Some in the components industry say that only electroplated tin will grow electrically conductive tin whiskers. Yet many engineers insist that any form of pure tin will grow whiskers.

The voices of concern over the whiskering effect on components are not being encouraged. “Environmentalists are trying to force lead-free solder,” explains a Lockheed Martin engineer who asked not to be identified since he expects there would be reprisals if he airs his concerns publicly. “The lead in tin solder [about 2 or 3 percent] for some unexplained reason keeps the tin from forming little dendrite-like whiskers.”

The Lockheed engineer notes that some companies have used the process of dipping the pure tin in a lead/tin mixture to inhibit the whisker growth. However, he also notes that if the solder is jeopardized by a scratch of other mechanical disturbance, the inhibitive coating may no longer protect the pure tin solder. Even though the military is exempt from RoHS and other emerging environmental legislation, the military buys as much as 90 percent of its electronic products off the commercial shelf, so tin-only products will still find their way into military applications.

One of the concerns among engineers is that the whiskering effect develops over a long term, so we may not see the effects of whiskering immediately as the industry starts making products with tin-only parts. If your cell phone quits operating because of a short due to a tin whisker, you throw it out and get a new phone. But engineers are more concerned about whiskers causing failures in more sensitive electronic devices. “The hi rel [high reliability products] users such as the Department of Defense and the space industry need to stand up against the European environmentalists and the U.S. Environmental Protection Agency,” says the Lockheed Martin engineer. “The risks [of failure] are too great to let a component that costs a few cents cause a million-dollar system to malfunction.”

As well as concerns about expensive equipment failure like the Galaxy 4 satellite, engineers are concerned about potential problems with life support equipment. “What if we get failure due to tin whiskers in a piece of medical equipment involved in life support?” asks the Lockheed Martin engineer.

In the commercial world of electronics, companies are moving quickly to comply with RoHS. The new tin-only components are going into commercial airplanes. Engineers are concerned that shorts caused by tin whiskers can potentially cause heat and perhaps fire as well as causing failures in electronic equipment used in jet control systems. As one distribution executive recently put it, “I certainly wouldn’t want to be on the first flight of an airline built entirely with tin-only components.”

This is the Part VII in a series of articles:

Part I: Industry braces for the lead-free conversion

Part II: Progress on lead-free components spotty

Part III: IDT: 99 percent lead free already

Part IV: Actel goes green on 100% of its FPGA products

Part V: Lead-free parts: Welcome to the messy supply chain

Part VI: Are the military and telecommunications industries off the hook on RoHS?

Part VII: Will electronic equipment fail from tin-whisker shorts?

Articles originally from Electronic Source Book