DAU GLOSSARY DEFINITION
Lead is a serious health hazard and an environmental risk, resulting in a focus on alternate substances and solders. While those alternatives (typically tin solder) are safer, and seemingly appropriate for consumer applications, the DOD has experienced reduced joint integrity, component reliability, and increased failures and maintenance costs. Although both DOD and industry are working to address the concerns, so far there are no effective and accepted tests to determine the susceptibility of plating to reduced joint pliability and reliability. Thus far, there is no mitigation technique that guarantees the protection required for high-reliability weapons systems except the reintroduction of small amounts of lead to the tin. From the Department's perspective, the lead-free transition is uncontrolled, but is proceeding regardless of military preparedness or availability of alternatives.
Leaded solder has been in use for decades, and has a proven technical performance record. It is reliable, available and low cost and, from an engineering standpoint, it is known and well understood. It provides solid performance in military applications that are more severe than civilian applications, which include temperature and humidity extremes, high altitude, vibration and shock, immersion, and so forth.
Unfortunately, the hazards and risks of using lead have driven civilian industry and manufacturing to identify and leverage alternate substances and solders. While those alternatives are safer, and seemingly appropriate for consumer applications, DOD applications have experienced reduced joint integrity, reduced component reliability, and increased failures and maintenance costs. Often this is a function of reduced joint pliability, or of 'tin whiskers', which are tiny hairs or physical abnormalities that 'grow' over time, spontaneously, from lead free tin-based finishes. These naturally occurring conductive, crystalline structures can create shorts, fires, and system or optics failures over long periods of time - or in some cases quite rapidly! While such risks may be acceptable in some applications, or when judged purely from an Environmental Safety and Occupational Health (ESOH) standpoint, the resultant reliability issues have been felt in DOD for years.
A study done at the US Naval Air Warfare Center Weapons Division (NAWCWD) indicated that about 25 percent of air- and surface-launched weapons, such as the Tomahawk and Sidewinder missiles, and the Joint Direct Attack Munition (JDAM) have experienced component failures due to tin whisker issues. Through 2002, at least six satellites sustained partial or complete loss due to tin whiskers, and there were also problems reported with the F-15 Eagle radar, the Patriot missile, and the Airborne Warning and Control System (AWACS) aircraft, and even the space shuttle. That time period coincides with civilian industries ramping up compliance with new international mandates such as the Restriction of Hazardous Substances (ROHS), suggesting there may be yet more difficulties to come as tin solder becomes more predominant. Although both DOD and industry are working to address the concerns, so far, the DOD has no effective and accepted tests to determine the susceptibility of plating to whiskering. And no mitigation technique guarantees the protection that the Department requires for high-reliability systems except the reintroduction of small amounts of lead to the tin; the lead-free transition is not controlled from DOD's perspective but is proceeding regardless of military preparedness or availability of alternatives.
Other problems include disposal of leaded components as they are phased out; viability of technician training for new materials; reliability and engineering data for standardized lead-free alloys; metallurgical phenomenon caused by thermal, compressive or other stresses and which can cause short circuits; plasma vapor arcing, or visual/physical contamination; and a lack of overall DOD policy on the matter.