What is the percentage of tin to lead in the solder that we use in electronics?
Environ Wellness Perspect. 2005 Oct; 113(ten): A682–A685.
Environews
Innovations
Getting the Lead Out of Electronics
The electronics industry is learning to do without: information technology is having to abandon one of its long-fourth dimension staples, pb–tin can solder. For decades lead–can solder has been used to adhere electronic components to printed wiring boards. However, with the torso of bear witness pointing to serious adverse health effects of lead, the search for a replacement has spawned intense effort in the electronics manufacture and in universities. Now scientists think they may have found some promising leads: solders made of alternative alloys and polymer formulations known equally electrically conductive adhesives (ECAs).
The Linchpin of Electronics
Solder is the "linchpin of electronics manufacturing," says Jack Geibig, interim managing director of the Eye for Clean Products and Clean Technologies at the University of Tennessee. "Without it, it'southward hard to reach a proper electronic connection that is durable and reliable."
Lead has been ideal for solder. In fact, says Carol Handwerker, chief of the metallurgy sectionalization at the National Institute of Standards and Engineering, "The whole electronics infrastructure was designed effectually the melting point and physical properties of [pb]." Pb is malleable and thus easy to piece of work with, and it doesn't fracture, she says. When pb is combined with tin in the correct proportion (63% can to 37% lead), the resulting alloy has a low melting betoken of 183°C, which is another advantage, Geibig says: "If yous're not operating at actually high temperatures, you have more control over processes, and so that the processes aren't sensitive to slight temperature variations, which are costly to control." Depression temperatures also mean less strain on the equipment and materials (such as printed circuit board and components) that must be heated every bit office of the assembly process.
The master impetus for the industry to leave lead behind is a ban on lead in electronics imposed by the European Marriage. Under the Restriction of Hazardous Substances directive, equally of 1 July 2006 lead must be replaced past other substances in electronic equipment. (The directive likewise bans mercury, cadmium, and hexavalent chromium.) Any electronic components bound for Europe are subject to the ban.
Lead is not a problem when contained in electronic equipment, says Robert Donkers, an environmental counselor for the European Commission who is based in Washington, DC. Nevertheless, when electronic components are deposited in landfills, he says, people may scavenge for equipment and break it open up, or the lead may leach out of landfills and into drinking water. The chance is compounded in countries that receive massive imports of electronic waste. In Communist china, for example, unprotected workers, including many children, strip recyclables out of electronic components in a cottage industry of sorts [see "eastward-Junk Explosion" in the April 2002 result of EHP].
Atomic number 82 exposure, even at depression levels, is well known for its harmful effects on children, resulting in lowered IQ. Lead as well affects the ability to pay attention. Children exposed to low levels may appear hyperactive and irritable, co-ordinate to the American Academy of Child and Adolescent Psychiatry. The electric current maximum allowable level for blood lead in the United states is 10 micrograms per deciliter (μg/dL).
Alternative Alloys
The main approach to replacing pb in solder has been to look for other metals equally substitutes. Electronics manufacturers began to wait for alternative metals in the 1990s, notes Handwerker, when now-abased proposals were existence discussed in the United States to ban atomic number 82 in electronics.
Ronald Gedney, a consultant for the International Electronics Manufacturing Initiative (iNEMI), a technology consortium, has been intimately involved in the search for alternatives. He says that a search by industry experts for possible replacements for lead–tin solder winnowed down 75 metal blend alternatives to about half a dozen. "We decided the biggest benefit for the industry would be to pick i solder, concentrating our development and research efforts on one blend and making it piece of work," he says.
The industry eventually selected a can–silver–copper combination equally offering the most reliability and ease to work with as a replacement. The conception—95.v% tin can, 3.9% silvery, 0.6% copper—is besides known as SAC solder, for the first letters of the chemical symbols of each of the elements (Sn, Ag, Cu). "Tin–silver–copper appears to take at least equally expert reliability if not higher reliability than tin–lead," says Handwerker.
Furthermore, according to a 2005 draft report issued by the U.South. Ecology Protection Agency titled Solders in Electronics: A Life-Cycle Assessment, silver was "rarely encountered above the detection limit" in constructed landfill leachate created to examination the stability of electronics components. Silver—which is regulated as a chancy fabric—is toxic to aquatic life.
With a melting signal of 217°C, SAC solder as well is closest in melting point to the conventional lead–tin can solder. This does mean, even so, a nonetheless-unquantified increase in energy utilisation. Furthermore, the college temperature may pose problems for the electronics industry. Higher temperatures mean more stress on components and the entire manufacturing process, notes Geibig. Higher temperatures also mean increases in the time information technology takes to make products, considering more time is required to heat and absurd the products during the class of their manufacture.
SAC solder is used widely in the industry today. However, many of the components existence made could non withstand the higher temperatures, says C. Michael Garner, director of materials technology operations at Intel: "That required re-engineering and getting new materials, not only for newer products merely for older products. All the older products that had been in production for ten or xv years had to exist converted over to high temperatures." He says it has taken a massive effort to integrate the new solder into production processes.
In that location are also short-term consequences of using the new solder. Someday there is a change in materials, there is a learning curve in using the new materials, says Karl J. Puttlitz, who managed IBM's efforts to reduce lead in its products earlier he retired final twelvemonth. He anticipates the occurrence of more manufacturing defects as a event of the changeover. "We tin expect that at to the lowest degree initially the failure rates [of products] will increase," he says. In fact, he notes the industry has asked for exemptions to the European union pb ban in certain critical electronic components where lives and security might be involved, such as equipment used in hospitals, until a track record is established with consumer goods such as cell phones and digital cameras. (The EU directive does permit exemptions to the lead ban if replacing lead is technically or scientifically impractical or if negative wellness, environmental, or safety consequences of replacing lead outweigh the benefits of the ban.)
A Stickier Approach
A more experimental alternative to pb–can solder is the utilize of ECAs. These are polymers, such as silicone or polyamide, containing tiny flakes of metals such as silver. The polymers adhere to the printed circuit boards, and the metallic flakes conduct electricity.
ECAs offer a range of advantages, notes C.P. Wong, a professor in the School of Materials Science and Engineering at the Georgia Found of Technology who is regarded by many in the field every bit the leading researcher in this new engineering. Silverish'southward electrical conductivity is very high, and its electrical resistance is very depression, he points out. "If the current-carrying capability [can be additional], ECAs can supercede solder," he says.
And in that location is another benefit. The temperature required to employ ECAs to excursion boards is far lower than that required for lead-based solder—150°C compared to 183°C. "You save energy, number one," says Wong. "Number two, you subject all the components to lower temperatures and thus less thermomechanical stress. That enhances their reliability."
Preliminary studies comparing parts using ECAs instead of solder, such as a Finnish study presented in 2000 at the 4th International Conference on Adhesive Joining and Coating Technology in Electronics Manufacturing, suggest that ECAs boast a much tighter bail than solders—perhaps an order of magnitude better, says James Morris, a professor of electrical and figurer engineering at Portland Land University. But he adds this research has to be replicated before it is regarded as valid.
ECAs are bachelor for a small number of applications requiring low power—for instance, liquid crystal displays—though they are non ready for the market in full general, where greater amounts of current are needed. Wong is working to enhance their ability to deport current. He is adding molecules of dicarboxylic acid to the silver flakes, which provides a link between the flakes, allowing for efficient and quick conduction of electric current. "It looks like it tin can exist as good equally or even better than atomic number 82–tin solder. We demonstrated that it works [in a presentation at the March 2005 national meeting of the American Chemic Society], just we yet demand further research and evolution," says Wong.
Wong and his collaborators are as well using some other means to boost the capacity to comport current—self-assembled monolayers. These are single layers of sulfur-containing molecules known every bit thiols that are attached to gilt pads in the electronic device. At less than ten angstroms (10 ten-billionths of a meter) in length, the molecules chemically bind to the gold pads in the device and the board, providing a direct electrical connection.
Notwithstanding more work is needed on these structures, notwithstanding, considering they brainstorm to fail structurally if the component heats up above 150°C. And there are other concerns about ECAs. With fourth dimension, notes Wong, the ability of ECAs to conduct electricity drops, and resistance to electricity increases. Another business is moisture. "Water is absorbed by polymers, in general," says Morris. That can encourage corrosion, he says, and may cause other equally notwithstanding unknown problems, he says.
Wong also points to the need for ECAs to become tougher and then they can withstand the force of being dropped. Ane way to do this, says Wong, is to develop polymers that are rubberized and made more elastic, then they won't break. Finally, Garner reiterates that these materials accept not been reliable for conveying moderate to high amounts of current nether normal operating conditions.
Wong and Morris are optimistic that with more research and development, ECAs tin be successful alternatives to lead–can solder. And Puttlitz does see a place for them in consumer electronics such as cell phones and digital cameras, which are not "mission critical" applications where reliability is a affair of life and death equally in medical monitoring equipment or shipping electronics.
Solder Replacement Soldiers On
Even every bit efforts to supercede lead in solder motility ahead, in that location still appear to be concerns about the bear on that newly implemented metals volition have on human and environmental health. "The alternatives to lead have not been researched also every bit lead in terms of potential health and environmental impacts," says Oladele A. Ogunseitan, a professor of ecology health, science, and policy at the University of California, Irvine. "When the Europeans said industry must become rid of pb, they didn't say you must replace lead with something that is apparently safer," he notes wryly. Information technology is important, he adds, to keep looking for lead alternatives that are environmentally benign.
Indeed, the draft Solders in Electronics written report indicates that no metal culling to lead is free from environmental concerns. For instance, whereas lead may pose a greater public health problem than SAC solder, the latter uses noticeably more than energy than lead–tin solder.
Just the presence of today's substitutes is good enough for Donkers. "Since there are alternatives, we have chosen not to have pb in the products anymore," he says. And while he does acknowledge that at that place are relatively few data on the impact of the electric current lead solder alternatives, he asserts that "in terms of agile policy, you cannot always look till you have complete certainty, because in the concurrently a lot of people get exposed [to lead]."
Sticking with the trouble.
Electrically conductive adhesives are one alternative to pb–can solder being tested in the search for healthier electronics.
The alloy alternative.
Can–silver–copper solder offers a safer solder than the lead–tin blend, and inquiry is continuing to address limitations on its employ.
Current advances.
Researcher Grace Yi Li holds samples of electrically conductive adhesives being studied at Georgia Tech's School of Materials Science and Technology. Such adhesives may one day supplant lead-based solders.
Suggested Reading
- Geibig JR, Socolof ML. 2005. Solders in Electronics: A Life-Cycle Assessment (Draft). Environmental Protection Agency, Office of Pollution Prevention and Toxics. Available: http://www.epa.gov/dfe/pubs/solder/lca/index.htm
- Li Y, Moon K, Wong CP. Electronics without lead. Scientific discipline. 2005;308(5727):1419–1420. [PubMed] [Google Scholar]
- Puttlitz KJ, Stalter KA. eds. 2004. Handbook of Lead-Complimentary Solder Technology for Microelectronic Assemblies. New York, NY: Marcel Dekker.
- Schoenung JM, Ogunseitan OA, Saphores J-DM, Shapiro AA. Adopting lead-costless electronics: policy differences and cognition gaps. J Ind Ecol. 2004;8(iv):59–85. [Google Scholar]
Articles from Environmental Health Perspectives are provided hither courtesy of National Institute of Environmental Health Sciences
Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1281311/
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