Reliability military electronics

Anon, Reliable Military Electronics , ArvICP 7C8-124, Ibid (1976)... 

Military Handbook 217E (MIL 217E) establishes uniform methods for predicting the reliability of military electronic equipment and systems. There are two methods of reliability predictions, namely parts count and parts stress analysis. 

RAC publications include data summaries for specific component types, such as hybrid microcircuits, small, medium and large-scale integration digital devices, linear and interface devices, digital monolithic devices, and discrete semiconductors. In addition, there are reliability and equipment maintenance data books that provide the failure and repair time data on military electronic equipment by application such as subsystem. 

Reliability data are available for many adhesives used in space environments for different orbits, different radiation, and different thermal-vacuum conditions. These data are available from approved materials and processes lists from NASA or from contractors for programs such as the Space Shuttle, Space Station, GPS, Hubbel telescope, and numerous satellite systems, some of which have been in orbit for over ten years. Adhesives used in military electronics have also been proven highly reliable in fighter planes, navy ships, ground and air communication systems, and navigation systems. 

Many North American companies are concerned that lead-free components and assemblies will not meet the reliability or functionality requirements necessary for high-end equipment supplied to banks, air traffic control systems, web-based businesses, and other mission-critical applications. Accordingly, manufacturers of aerospace and military electronics have no plans to introduce lead-free solders. There are too many reliability concerns to utilize lead-free solder materials in high-reliability equipment related to the mechanical characteristics of the materials themselves and the effects of high temperatures to process them. The effect of new and modified intermetallic compound phases within solder joints and at the interfaces is yet an additional concern, and there are many more. 

Tin whiskers are thin single crystal filaments that grow from electroplated tin and tin-rich coatings after plating. The propensity of tin or tin-based coatings to spontaneously form whiskers is well documented and has been known for some time [13,14]. Tin whiskers appear in many different physical shapes and sizes, as shown in Fig. 19. Much has been written on this subject as it is of great concern within the electronics industry as tin whiskers have been known to cause short-circuit field failures in commercial and military electronic products. Pure tin is not the only candidate to possess a tin whisker risk, and in fact all Sn-rich Sn alloys including Sn-Bi, Sn-Ag, Sn Cu, and especially Sn Zn pose reliability risks from the threat of tin whiskers. 

Reliability Prediction of Electronic Equipment (Military Handbook 217E)... 

Reliability Analysis Center Handbooks Government and Military Data summaries of hundreds of records by component and environment Electronic component reliability data. i.e. microelectronic devices. high technology components 110. 

Typical applications are relay switches, connectors, terminal strips, electronic parts, and many other military applications where zero defect programs and electrical reliability are of utmost importance. 

The ability of a solder mask to protect conductors from physical and chemical deterioration and to insulate adjacent circuitry is a major consideration of PCB manufacturers. The Institute for Interconnecting and Packaging Electronic Circuits (IPC) has defined the requirements for the qualification and performance of solder masks in the Standard Specification IPC-SM-840 (A). The specification defines classes (1, 2, and 3) to reflect progressive increases in sophistication, functional performance, and testing methods. These classes try to provide PCB manufacturers with assurances of reliability. For example, Class 1 requirements provide the reliability needed by commercial boards used in radios, televisions, and small appliances. Class 2 is for computers and Class 3 for military and life-dependent products. 

MIL-HDBK-217B (1974), Reliability Prediction of Electronic Equipment, Military Stemdendization Handbook, U.S. Department of Defense, Washington, DC. 

Thus, components that are surface mounted with adhesives must maintain their strength and electrical properties during and after these combined environments and after repeated stresses. To assure reliabiUty, numerous accelerated tests have been developed and incorporated in military and industry specifications. Among specifications governing the mechanical, electrical, and quaUfication requirements for electronic components, modules, subsystems, and systems, most of which could not be met without using qualified and reliable adhesives, are MIL-STD-883, MIL-STD-810, MlL-STD-202, and MIL-PRF-38534. ... 

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