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Tin Whisker Mitigation Methodologies: Report from SMART Group, Part 1
Using the analogue of two sword-fencers for illustration, Wickham explained different failure modes: Please first log in with a verified email before subscribing to alerts.
The higher current densities tended to favour the formation of large eruptions, rather than filament whiskers. Other resources include work performed in to benchmark the Pb-free technical knowledge base as well as develop 00055 roadmap and plan to close those technical data gaps [13, 14].
While the Pb-free movement may appear ominous and challenging, there are tools and resources available to the designer. 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. Although equipment designed to teia into space was exempt from the RoHS Geiia, the reliability of space hbb clearly depended on the integrity of PCBs, components and assembly processes.
A proprietary bright tin plating process was used. But how do we set about mitigating against such failure where the use of pure tin finished components is unavoidable?
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 hbb strategies for tin whisker mitigation. 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.
Furthermore, the guide highlights Pb-free concerns, as they are encountered 22 the phases which generally reflect the product development cycle used by Jb, Defense, and High-Performance systems industries. Summarizing at a high level, these challenges represent risks associated with 1 durability of the interconnection and 2 deleterious effects of tin whiskers.
He began his presentation on problems associated with whisker growths with 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 defining standard for tin whisker susceptibility of tin and tin alloy surface finishes was JEDEC JESDA, an accelerated test used by egia manufacturers, but there was some doubt as to the reliability of results since tin whiskering was such an unpredictable phenomenon.
With Professor Geoff Wilcox taking over as moderator, Charles Cawthorne began his own presentation by remarking that, since first observed inand despite many geoa of study, the mechanism of tin whiskering was still not fully understood and predictive modelling was not yet possible.
As Pb-free technology increasingly becomes the standard for electronic interconnects and finishes, engineers must cope with the various challenges posed by this material. This Standard establishes processes for documenting the mitigating steps taken to reduce the harmful effects of tin finishes in electronic systems.
Possible future work would investigate the effects of vibration and forced air cooling. 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.
This standard is not included in any packages. And he quoted instances of systems failure in communications satellites originating from tin whiskers.
It was intended to continue ageing the test vehicles and review failures after a further six months, and to visually inspect 00005 assemblies again after twelve months, also to build control assemblies to investigate the effect of temperature during coating. Engineers will need to “act like engineers” in order to comprehend this information and apply it to their needs.
Each batch of eight boards was delivered to consortium partners for coating and returned to NPL for testing. A Circuitnet Media Publication.
Although higher currents would cause instant burn-out, in high-vacuum conditions a short circuit could result in a plasma discharge. Standards Subsctiption may be the ub solution.
Hv had been a move away from component termination material type, structure and processing as specific mitigation strategies.
Tin Whisker Mitigation Methodologies: Report from SMART Group, Part 1
The deposit characteristics studied were thickness, grain size, morphology, orientation, intermetallic formation and elemental diffusion effects, under varying conditions of temperature, humidity, thermal cycling and applied external stress. 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. He showed several examples of actual failures, and other instances where whiskers had grown but not yet been detected electrically.
Standards Subscriptions from ANSI provides a money-saving, multi-user solution for accessing standards. 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.
Using a tin plating process deliberately chosen for it high propensity to whiskering, NPL had developed a parallel plate test vehicle that had been enabled electrical detection of failure. 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. A series of collaborative projects had been carried out at the National Physical Laboratory to evaluate conformal coating as a tin whisker mitigation strategy for printed circuit assemblies.
Plated brass, tin-plated brass with a copper barrier layer, tin plated steel, tin-plated steel with a copper barrier layer, all displayed their own characteristics, sometimes predictable, sometimes not, but fused tin plating showed no whisker nucleation on any of these substrates during the 32 years of the study. 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 relevant 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.
One observation was that failure predominantly occurred at the edges of plates, where full coating thickness was not maintained around the right angle bend, and this geometry was a characteristic feature of component leads.
A distinguished 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.