Defense and aerospace industries are bracing for a spike in the cost of manufacturing high-tech electronics for the U.S. government, as well as for a possible rise in the number of catastrophic failures of pricey military hardware.
The culprit is a three-year-old mandate by the European Union to eliminate lead from coatings and solders that are widely used in the production of electronics. The regulations — intended to ensure environmentally safe manufacturing of electronics — also are being adopted by key technology producers such as China, Japan and South Korea. Although the United States has no such rules, it is being greatly affected because it buys most of its electronics from global suppliers.
The issue for U.S. defense and aerospace suppliers is that the lead-free electronics that will increasingly dominate the commercial market are known to cause failures in military and space systems, government and industry experts say. NASA and the Defense Department’s Missile Defense Agency alone have documented $1 billion worth of catastrophic damage to satellites, missiles and other equipment. The failures were attributed to a mysterious phenomenon known as “tin whiskers” — the growth of hair-like substances on electronic assemblies that can cause short-circuits. Traditionally, lead has been added to solders and coating materials to stifle whiskering. Some scientists say that tin whiskers tend to occur when there is less than 3 percent lead in the coatings of a component.
The mandatory removal of lead from coatings and solders raises the specter of more malfunctions in military and space equipment as more components are acquired from global suppliers that are gradually shifting their manufacturing processes in order to eliminate all lead.
Microelectronic assemblies are now essential components of just about every military system. Solders are critical to the integrity of the electronics. While the risk of equipment failures may be relatively low for the commercial market that focuses on consumer products, it is huge for the Defense Department and NASA, says Craig Hillman, chief executive officer of DfR Solutions in College Park, Md., a Defense Department contractor. Lead-free solders are acceptable for making consumer electronics such as cell phones and laptops, which are regarded as disposable items that can be easily and inexpensively replaced if they fail. That is not the case with multibillion-dollar military systems.
The U.S. defense industry has no experience working with lead-free solders and coatings, Hillman says. Almost 100 percent of the Defense Department’s electronics have tin-lead components.
Government contractors will be expected to modify lead-free commercial components in order to meet strict reliability and performance specs, Hillman says. That will drive up the cost of military equipment significantly. He estimates that adapting lead-free items into military-acceptable assembly lines will incur cost premiums of 50 percent to 200 percent.
“We can’t move away from COTS [commercial off-the-shelf] technology,” says Hillman. “We have to go lead-free, but we have to do it in a low cost and low risk fashion.”
The Defense Department needs to fund additional research into how to deal with lead-free electronics, Hillman said.
The Pentagon’s Defense Microelectronics Activity — a small agency that reports to the office of the secretary of defense — has for years been developing and testing lead-free solders and assemblies for military systems. But these projects are still in the experimental stage. One industry source says that DMEA tests showed that the lead-free assemblies performed poorly compared to the tin-lead solder used in military systems.
The Defense Department decided in the 1990s to phase out many of its costly military-unique components and incorporate commercial technology into its weapon systems to save time and money.
There is no turning back from that. It would be now prohibitively expensive for suppliers to build dual production lines, one lead-free and one for leaded systems, Hillman says. For the Defense Department, this would mean not just higher prices but also availability problems that it sought to address by switching to commercial technologies.
Hillman says he expects the Defense Department to eventually come up with an acceptable lead-free solder replacement, but that could take years.
Meanwhile, the changeover to lead-free systems now is adding costs to many military programs because they have to customize microelectronics — not just for new products — but also to fix existing systems that are not compatible with lead-free technology.
Because the materials used in the production of electronics are prone to corrosion, coatings are added to retard the process. Cadmium, zinc and tin have commonly been part of these protective layers.
For the last 50 years, lead has been mixed into these coatings and added to tin solders to slow down whiskering, even though whiskers sometimes occur for reasons that are still unknown.
Whiskers, which are a tenth of the diameter of a human hair, grow long enough to span the gap between components and cause a short circuit.
Tin whiskers are causing a “steady drizzle” of failures in defense and commercial electronics, says Henning Leidecker, chief parts engineer at NASA’s Goddard Space Flight Center in Greenbelt, Md.
He and a team of scientists are investigating the phenomenon and tracking instances of failures. Their research, posted on NASA’s website, reflect only 10 percent of known cases, which include a couple hundred instances in which electrical systems in military and satellite systems have been shut down as a result of tin whiskers that caused shorting. Some of these failures also took place at nuclear power plants.
“We’ve only been able to track these problems in very expensive systems where failure is not an option,” he says.
Leidecker says that the other 90 percent of the cases is not releasable to the public because the information is proprietary.
NASA became involved in the project after a commercial satellite, Galaxy IV, stopped working in 1998 and shut down 35 million pagers along with other communications. After failing to recover the system, engineers attempted to initiate the back-up system, which also did not respond. The builder of the satellite, the Boeing Co., tracked the problem down to a tin whisker that had grown in a component.
“This has happened in other satellites as well,” he adds. In at least one case, the culprit was whiskers growing from zinc coating.
The problem is not a new one at all. During World War II, American Radio Corp. in New Jersey won a contract to build 50,000 radios to help military pilots land at blacked-out airports. When the radios suddenly stopped working, engineers learned that the cadmium coatings on the capacitors had grown whiskers long enough to bridge the gap from the rotor to the stator, which subsequently killed the operation of the capacitor and the radio.
Bell Telephone Laboratories in the early 1950s acknowledged that cadmium plated parts grew whiskers, so researchers urged a switch to zinc or tin plating. But then the AT&T telephone system began losing entire racks full of multiplexed transmission lines — thousands of lines would go dead at a time. The lab traced the cause to zinc and tin whiskers growing from these coatings.
What they learned was that pure tin could not be used in the presence of electrical circuits where different conductors, spaced closer than a millimeter or two, were carrying power or signals, says Leidecker.
Bell Labs subsequently pursued a program to figure out what element of the periodic table would mix with tin to prevent the growth of whiskers. As little as a half percent to 1 percent of lead could quench the growth effectively, researchers discovered. As a result, manufacturers began adding 1 to 3 percent of lead to coatings. While lead did not completely eliminate whiskers, it helped to drop the density of whiskers on a surface by one to two orders of magnitude. Up to 14,000 whiskers per square centimeter of a tin-plated surface is a common density of growth.
Lead also shortens any whiskers that do grow — rarely are they longer than a tenth of a millimeter. The longest whisker ever found was 25 millimeters long, or one full inch, which was discovered on a tin-plated component aboard the Space Shuttle Endeavor.
The problem of whiskering is not limited to military and space equipment. “It’s happening much more in the civilian market,” says Leidecker. But consumers do not hear as much about it because lawyers are often involved and commercial companies do not like to advertise problems, he points out. More often than not, they simply aren’t tracking it.
“When a cell phone or a wristwatch stops working, no one spends the $500 to $5,000 that a robust failure analysis takes. You throw it away, or you return it to the company, and the company throws it away,” says Leidecker. In the defense and space realm, throwing away failed equipment is not an option. “We’re the people who carry out our own failure investigations. We advertise what we find,” he says.
Whiskers can be hard to detect. Sometimes when they bridge across components and there’s enough current and voltage available, the whisker will vanish into a puff of tin vapor, Leidecker says. Testing gear inspects soldering jobs for anomalies but may miss them as well. Whiskering often has been dismissed as a myth because the phenomenon is witnessed by so few.
And because there are so many skeptics out there, little is being done to sound the alarm on the issue. The problem may become exacerbated as the European Union and Japan have aggressively pursued the control of hazardous substances in electronics, including lead.
“We can look forward to legislation saying that we have to keep the lead out of our products, including the lead that would be used in quenching whiskers in tin coatings and in solder,” says Leidecker. Already, the unintended consequences of following such regulations are becoming apparent.
A consortium of about three dozen companies that manufacture components for the Swiss watch company, Swatch, adopted a new solder after becoming subject to the EU’s reduction of hazardous substances legislation. The traditional blend contained 40 percent lead. But the new lead-free solder is 99.5 percent pure tin and .5 percent copper.
Six weeks after the switch, 5 percent of the watches no longer worked, says Leidecker. Upon inspection, the company discovered that 30 percent of the watches had grown tin whiskers, which were shorting out the quartz crystal upon which the timepiece is based.
The defect resulted from the extraction of lead from the solder, says Leidecker.
A similar problem has been detected in automobiles. Vehicles recently arrived from the manufacturing plant have been known to not start in the showroom.
Other lead-free solders are being patented. One is tin-based, with 5 percent copper and a smaller percentage of silver. “We’ve watched those grow whiskers as well,” says Leidecker.
While the use of lead is still legal in the United States, there is a monetary incentive to stop its use. Pure tin is cheap. “I believe you can still plate in this country using lead, but disposal of the plating baths now requires very expensive cleanup,” says Leidecker. Companies contend that if they use lead, the product becomes expensive to the point where it’s no longer competitive. Plus, they cannot sell the lead-containing product in Europe or Japan because of environmental regulations there.
Besides whiskers, there are other problems associated with the lead-free solders. New solders, particularly the tin-silver-copper alloys, require 20 to 30 degrees higher temperatures to populate the circuit board. “This is destroying boards. This is destroying parts,” Leidecker alleges. Boards originally were designed for the cooler temperatures involved with lead-tin solder assembly.
Some companies add other materials, such as bismuth or antimony, to solders. Such lead-free solders can do the job, says Leidecker, but the problem is that not all solders are compatible. Sometimes when they intermix, the result is brittleness, and parts can even fall off the board.
“One has to be meticulous about which solder is used at every stage of the assembly of a board, including any necessary rework,” says Leidecker. “If you mix the solder used for this rework in a way that’s unfortunate to the existing solders, then you have built in a death wish that will probably manifest later under thermal cycling, after you shift the boards.”
The switch to lead-free solder has exposed a growing rift between manufacturers and those on the receiving end who are responsible for the reliability of the products. Manufacturers are interested in selling as many items as possible. For military program managers, the priority is to ensure bombs don’t go off accidentally. “There are folks who know this is a problem and they’re scared to death of the impact on reliability coming from whiskering and coming from the shift in performance in solders,” he says.
At NASA, lead is required in solders and tin coatings. Inspectors scrutinize incoming parts, and they are finding that between 1 percent and 3 percent of parts contain no lead at all. “That’s why we measure the lead in the tin plating,” says Leidecker. “We find a persistent drizzle of about 2 percent that is pure tin.”
The use of lead, however, is not a panacea for solving the whiskering problem.
There has been only one case of whiskers growing from leaded material — aboard NASA’s ICE-SAT — a satellite that measures the thickness of ice in regions of the Earth, particularly in Antarctica and Greenland. In ground tests, whiskers the thickness of a human hair that were growing from the lead-tin solder destroyed one of the lasers in the system.
But lead is still the most effective measure against whiskering, experts say. Adding a percentage or two of gold to a solder also is effective at quenching whiskers, but it is an expensive alternative.
The best solution, Leidecker says, is to put in barriers so that whiskers are captured as they grow, or to put conformal coatings on surfaces to prevent conductive contact. “That has been spectacularly helpful for us. If it weren’t for coatings in the Space Shuttle Endeavor, I believe we would’ve had problems,” he says.
Conformal coatings are built by spraying or painting on a resin. The most popular one is a urethane-based coating, under the brand name, Aerothane. But manufacturers do not like them for two reasons: they are expensive to put on, and they make assembling components more complicated.