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While considerable progress has been made in closing Pb-free knowledge gaps, the challenge of characterizing performance and reliability still needs to be addressed. The plan included a list of tasks necessary to provide ADHP engineers sufficient information to minimize risks associated with Pb-free solders and finishes.
But how do we set about mitigating against such failure where the use of pure tin finished components is unavoidable? Each batch of eight boards was delivered to consortium partners for coating and returned to NPL for testing. A egia group of experts gathered at Loughborough University in the East Midlands of the UK to share their knowledge with a room-full of engineers from the defence, aerospace and high-reliability electronics sector, at a seminar organised by SMART Group.
Dr Ashworth stressed that these observations related to the yeia proprietary electroplating chemistry used in the study, and that other commercial formulations might demonstrate different relationships between current density, deposit microstructure and whisker growth.
The factors influencing whisker growth were electroplating bath chemistry, whether pure tin or a tin alloy, bright or matte, electroplating parameters such as current density, temperature and agitation, and substrate, taking copper, brass and alloy 42 as examples.
Tin Whisker Mitigation Methodologies: The assemblies were constantly monitored at a test voltage of 15 volts with a series resistor to limit current to 15 milliamps. Dr Dunn had collected data on whiskering effects over a period of 32 years, using the C-Ring test to introduce tensile and compressive stress, with different metal substrates, barrier layers and tin plating thicknesses, and the results were shortly to be published.
Martin Wickham reviewed previous findings and gave an update on current work. This Standard establishes processes for documenting the mitigating steps taken to reduce the harmful effects of tin finishes in electronic systems.
Other resources include work performed in to benchmark the Pb-free technical knowledge base as well as develop a roadmap and plan to close those technical data gaps [13, 14]. The name was chosen around by a group of engineers from aerospace, defense, and harsh environment ADHE organizations. This paper presents a summary of efforts from document inception to document release.
Consequently, manufacturers of high-reliability electronics with RoHS exemption were left with no alternative but to manage tin-lead obsolescence by avoidance or mitigation. Since the introduction of the RoHS legislation inthe threat of tin-whisker-related short circuit failure from pure tin finished components has remained a major concern within the high-reliability electronics manufacturing industry.
Living With PB-Free in High Performance Engineering Design
And he quoted instances of systems failure in communications satellites originating from tin whiskers. Finally, a good number of texts and a continuously increasing amount of data is now available in the open literature.
Using a tin plating process deliberately chosen for it high propensity to whiskering, NPL had developed a parallel plate test vehicle hn had been enabled electrical detection of failure. He began his presentation on problems associated with whisker growths hg a remarkable time-lapse video recorded by researchers at Brown University, showing the initiation and growth of a tin whisker at a steady rate of about 1 micron per hour over a period of 40 hours.
The higher current densities geja to favour the formation of large eruptions, rather than filament whiskers.
geia std 2 pdf – P(1) –
Need more than one copy? Cawthorne reviewed the definitions of the mitigation control levels defined in GEIA-STD, commenting that the required level would normally be a function of the design authority in consultation with the customer, and that military applications would typically expect mitigation to at least Level 2B—risks 00005 primarily through mitigations, including design rules, and more likely 2C—risks managed more by avoidance and less by mitigation.
On behalf of ESA, a working group led by Dr Dunn had produced a comprehensive set of guidelines for creating a lead-free control plan, which described the problems, requirements and methods yb to the preparation of a plan for companies to control against the use of lead-free components and to ensure that pure tin did not find its way into the manufacturing chain.
Possible future work would investigate the effects of vibration and forced air cooling. A proprietary bright tin plating process geiw used.
Nine batches had bh built to date, together with control assemblies with no coating, all of which had shown extensive whiskering before any evidence was seen on the coated examples.
Upon reviewing these plans, several research consortiums and organizations embraced the plan and, to date, have addressed many gea the technical needs although the significant effort of obtaining sufficient data to develop Pbfree reliability models still remains unanswered . Furthermore, the guide highlights Pb-free concerns, as they are encountered in the phases which generally reflect the product development cycle used by Aerospace, Defense, and High-Performance systems industries. Standards Subscriptions from ANSI provides a money-saving, multi-user solution for accessing standards.
In summary, ggeia the standards had evolved, they had become increasingly definitive with regard to component-to-component spacing design rules.
Some key resources include the following set of standards and geix developed for working with Pb-free materials in various electronics applications: One observation was that failure predominantly occurred at the edges of plates, where full coating thickness was not maintained around the right hg bend, and this geometry was a characteristic feature of jb leads. Please first verify your email before subscribing to alerts.
This standard is applicable 0005 Aerospace and High Performance electronic applications which procure equipment that may contain Pb-free tin finishes. Whisker growth was reduced by increasing deposit thickness and by deposition at higher current densities.
This standard geeia not included in any packages. There had been a move away from component termination material type, structure and processing as specific mitigation strategies. Pulse plating could be used as a means of manipulating the grain structure and orientation of the tin deposit, and in some instances showed reduced whisker growth compared with direct current deposits. Trends for Printing Ultra Miniature Chips.
Using the analogue of two sword-fencers for illustration, Wickham explained different failure modes: Charles Cawthorne then introduced Dr Mark Ashworth of Loughborough University, who discussed the effect of plating methodologies, the first of two presentations describing research carried out at Loughborough into mechanisms and strategies for tin whisker mitigation. A Circuitnet Media Publication. It will take a combination of high-level design strategies and an effective set of guidelines to enable the ADHP engineer to develop mission-successful products and systems.
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Tin Whisker Mitigation Methodologies: Report from SMART Group, Part 1
Level 3 gwia whisker risks through complete avoidance. As the voice of the U. A remarkable observation was that in some instances it could be several years before whiskers began to grow, depending on the substrate and stress level.
Environment Impact on Assembly, Printing and Reflow. A whisker one micron in diameter could support geiz current of 10 mA. The body configuration of SMT electrolytic capacitors results in the solder joints being only partially visible for optical inspection purposes. He went on to discuss the detail requirements of Levels 2B, 2C and 3, with particular reference to the use of conformal coatings to form a physical barrier.