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Title (english): Process management for avionics - Aerospace and defence electronic systems containing lead-free solder - Part 2: Mitigation of deleterious effects of tin (IEC 107/160/DTS:2011)

Document type: Technical rule (draft)

Publication date: 2012-04

Date of Issue: 2012-04-23

Overview:

This current Part 2 of the standard series Process management for avionics - Aerospace and defence electronic systems containing lead-free solder defines processes for documenting the mitigating steps taken to reduce the harmful effects of Pb-free tin in electronic systems. This specification is applicable to Aerospace, Defence, and High Performance (ADHP) electronic applications which procure equipment that may contain Pb-free tin finishes. Due to a variety of real and potential health issues, many constituent materials used in the production of electronic products have come under scrutiny. The European Union (EU) has enacted two directives; 2002/95/EC Restriction of Hazardous Substances (RoHS) and 2002/96/EC Waste Electrical and Electronic Equipment (WEEE) that restrict or eliminate the use of various substances in a variety of products produced after July 2006. One of the key materials restricted is lead (Pb), which is widely used in electronic solder and electronic piece part terminations, and printed wiring boards. While these regulations may appear to only affect products for sale in the EU, due to the reduced market share of the Aerospace, Defence, and High Performance Industry in electronics, many of the lower tier suppliers are changing their products because their primary market is world-wide consumer electronics. Additionally, several Asian countries and United States (U.S.) states have enacted similar "green" laws. Many Asian electronics manufacturers have recently announced completely "green" product lines. The restriction of Pb use has generated a transition by many piece part and board suppliers from tinlead (Sn-Pb) surface finishes to pure tin or other Pb-free finishes. Lead-free tin finishes can be susceptible to the spontaneous growth of crystal structures known as "tin whiskers" which can cause electrical failures, ranging from parametric deviations to catastrophic short circuits, and may interfere with sensitive optical surfaces or the movement of Micro-Electro Mechanical Systems (MEMS) for example. Though studied and reported for decades, the mechanism behind their growth is not well understood, and tin whiskers remain a potential reliability hazard. Furthermore, the growing number of piece parts with pure tin finishes means there are more opportunities for whiskers to grow and to produce failures. It is important to state that that the nature and meaning of "risk" posed by tin whiskers may vary considerably across the range of users of this standard. As in any assessment of risk, the probability of occurrence and failure and consequence of occurrence and failure must be considered in each application. Potential whisker failure modes for a particular hardware/system application must be carefully considered when making the choice/determination of which Control Level(s) to apply. For example, whisker-prone leaded parts on circuit card used in a system that is under frequent/continual power may only incur parametric deviations or interrupts as individual whiskers grow and short to an adjacent lead. On the other hand, the same circuit card, employed in a missile subject to years of dormant storage, could grow many long whiskers into potentially catastrophic shorting conditions but the shorts will not occur until the missile is launched toward its target and results in mission failure. For the purposes of this Specification, risk refers to the chance and consequence of a failure due to a whisker, not just the chance of the presence of a whisker. This Specification is intended for use by those procuring, designing, building or repairing electronic assemblies that will use items with Pb-free tin finishes to document processes they use to assure performance, reliability, airworthiness, safety, and certifiability of those assemblies. It provides a framework to communicate and agree on the processes to be used to control and mitigate the use of Pb-free tin in these applications. This Specification addresses the risk of tin whiskers. However, the state of research into tin whisker risk still does not allow accurate quantitative estimates of the risk and reliability. This Specification defines three baseline Control Levels that detail the amount of attention that should be paid to the risk of tin whiskers: no restrictions on tin use, some restrictions on tin use, and prohibition of tin use. There are six informative annexes in this Specification: - Annex A.1 provides guidance on selecting Control Levels and performing risk assessments - Annex A.2 provides some background on various mitigation methods - Annex A.3 provides guidelines for performing tin whisker inspections - Annex A.4 provides some additional guidance on tin whisker risk analyses - Annex A.5 provides information on whiskers growing from bulk solder and joints - Annex A.6 provides a bibliography The responsible committee is K 684 "Prozessmanagement für Avionik" ("Process Management for Avionics") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Language: German, English