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== Materials ==
Until recently, electronics manufacturers could use whatever materials they deemed necessary to make their products, and make them reliable and long - lasting. Cadmium is a very toxic metal that was routinely used to plate electronic chassis, because it was corrosion - resistant and could be [[Soldering|soldered ]] to. But recent regulations in the US and Europe have banned cadmium in almost all products. ▼
Most electronic solder has been made with the same formula since World War II (and before, in the case of some manufacturers like Kester). Scientists knew that a mixture of 63% tin and 37% lead was the "eutectic mixture ", meaning it had the lowest melting point. Since it's difficult to mass - produce solder to such a close standard, most solder manufacturers simply get it as close as possible and call it "60 -/40 " solder. The difference is not critical (claims of some crackpots aside). Tin and lead are the least - costly metals that can be used in a solder, and give very reliable results when used properly, so the 60 -/40 mixture became the standard for electronics manufacturing. Solders made of bismuth can have a lower melting point, but are more costly and can have problems with reliable "wetting " of a wire or PC-board[[PCB]] pad. Indium solders are excellent, but indium is extremely expensive. Solders carrying a high percentage of silver are also costly and are prone to oxidation. So the 60 -/40 lead-tin /lead solder has been the most reliable, cost - effective mixture for more than 90 years. ▼▲Until recently, electronics manufacturers could use whatever materials they deemed necessary to make their products, and make them reliable and long-lasting. Cadmium is a very toxic metal that was routinely used to plate electronic chassis, because it was corrosion-resistant and could be soldered to. But recent regulations in the US and Europe have banned cadmium in almost all products.
Lead does one thing for solder that is still poorly understood today: it helps prevent a bizarre effect called "[ http[Wikipedia: //www.guardian.co.uk/technology/2008/apr/03/research.engineeringWhisker (metallurgy)|tin whiskering] "]. For some specialized applications, such as medical equipment or space - rated electronics, manufacturers will attempt to use a pure tin or tin -/silver solder, to avoid the toxicity or other problems of lead. WhiskersIn these cases whiskers can sometimes grow between electrical connections, shorting them out. ▼▲Most electronic solder has been made with the same formula since World War II (and before, in the case of some manufacturers like Kester). Scientists knew that a mixture of 63% tin and 37% lead was the "eutectic mixture", meaning it had the lowest melting point. Since it's difficult to mass-produce solder to such a close standard, most solder manufacturers simply get it as close as possible and call it "60-40" solder. The difference is not critical (claims of some crackpots aside). Tin and lead are the least-costly metals that can be used in a solder, and give very reliable results when used properly, so the 60-40 mixture became the standard for electronics manufacturing. Solders made of bismuth can have a lower melting point, but are more costly and can have problems with reliable "wetting" of a wire or PC-board pad. Indium solders are excellent, but indium is extremely expensive. Solders carrying a high percentage of silver are also costly and are prone to oxidation. So the 60-40 lead-tin solder has been the most reliable, cost-effective mixture for more than 90 years.
All well and fine--untilIn 2006 , when the EU promulgated the [ http[Wikipedia: //en.wikipedia.org/wiki/Restriction_of_Hazardous_Substances_DirectiveRestriction of Hazardous Substances Directive]] (RoHS ]) took regulationeffect. Along with banning cadmium plating, hexavalent chromium (also used to plate parts), and certain brominated chemicals that are used to make plastics more fire - resistant, it banned lead solder. Luckily thereThere are a number of exemptions that any maker of modular synthesizers can take, thus avoiding RoHS problems when exporting to Europe. But the maker still has to include an RoHS exemption sheet with every shipment to an EU country. Companies that mass - produce consumer goods, like cellphones, personal computers, appliances and the like, have no recourse but to use lead - free solder. ▼(Fair warning: audiophiles sometimes DIY electronics, and go around raving about hideously expensive, exotic solders. These solders, such as [http://www.cardas.com/content.php?area=oem&pagestring=Solder+and+Flux&content_id=19 Cardas solder], will not get you anything in the way of better reliability or connection quality. They are similar to the $8,000 power cables sold in high-end audio shops. If you really think this will make your synthesizer "sound better", feel free to waste your money. Similarly, people asking "which solder to use" in musician forums are often fed a line of crap by lunatics. No kidding: I have seen a few self-appointed experts, calmly telling people to use ''acid-core'' plumbing solder on their guitar amps. This will destroy the wiring. Very stupid.)
▲Lead does one thing for solder that is still poorly understood today: it helps prevent a bizarre effect called "[http://www.guardian.co.uk/technology/2008/apr/03/research.engineering tin whiskering]". For some specialized applications, such as medical equipment or space-rated electronics, manufacturers will attempt to use a pure tin or tin-silver solder, to avoid the toxicity or other problems of lead. Whiskers can sometimes grow between electrical connections, shorting them out.
▲All well and fine--until 2006, when the EU promulgated the [http://en.wikipedia.org/wiki/Restriction_of_Hazardous_Substances_Directive RoHS] regulation. Along with banning cadmium plating, hexavalent chromium (also used to plate parts), and certain brominated chemicals that are used to make plastics more fire-resistant, it banned lead solder. Luckily there are a number of exemptions that any maker of modular synthesizers can take, thus avoiding RoHS problems when exporting to Europe. But the maker still has to include an RoHS exemption sheet with every shipment to an EU country. Companies that mass-produce consumer goods, like cellphones, personal computers, appliances and the like, have no recourse but to use lead-free solder.
There are attempts being made by legislators in other countries to outlaw the RoHS substances. The US Congress has considered it, though with no action to date. The State of California will probably outlaw lead solder soon, with other states likely to follow.
60-/40 solder is still less costly than any of the more exotic solders being used, and although long- term reliability is still a subject of much argument, 60-/40 solder has a proven reliability track record going back to the 1920s. It is not unusual to find an 80- year- old radio whose soldered joints are still solid, shiny, and functional. Since PCs and cellphones tend to behave disposeda ofmuch orshorter die after two years or lessusage, tin whiskering may not be an issue. Only the future will tell.
==References==
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