NEMI revises tin whisker guidance.Herndon, VA -- A group of technology experts has issued new recommendations for testing assemblies for tin whiskers See metal whiskers. and evaluating devices with tin finishes. The recommendations by the National Electronics Manufacturing This article presents a typical manufacturing process of an electronic assembly. Component manufacturing Components such as resistors, capacitors and integrated circuits are generally made by specialized contractors. Initiative's Tin Whisker User Group update previous guidance released in May. The new guidelines (nemi.org/projects/ese/tin_whisker_activities.html), which include input from suppliers not found in the May version, have been submitted to IPC (1) (InterProcess Communication) The exchange of data between one program and another either within the same computer or over a network. It implies a protocol that guarantees a response to a request. and JEDEC The division of the Electronic Industries Alliance (EIA) that deals with semiconductor standards (officially, the JEDEC Solid State Technology Association of EIA). JEDEC was formed in 1958 when the Joint Electron Tube Engineering Council (JETEC) split into two Joint Electron Device to consider for standardization standardization In industry, the development and application of standards that make it possible to manufacture a large volume of interchangeable parts. Standardization may focus on engineering standards, such as properties of materials, fits and tolerances, and drafting . Among the updates: * Changed significantly the "qualification by similarity" matrix, dramatically reducing the number of tests (and associated cost) required by an individual supplier. * Eliminated the annual requalification requirement, replacing it with a simpler, supplier-defined, whisker-monitoring requirement. * Eliminated requirements for control samples that produce whiskers See metal whiskers. . * Provided options in the specification if tin-lead reference samples are not used or available for baseline whisker length comparisons. * Provided guidelines for optical inspection qualification as a possible alternative to SEM (scanning electron microscopy electron microscopy Technique that allows examination of samples too small to be seen with a light microscope. Electron beams have much smaller wavelengths than visible light and hence higher resolving power. ). * Eliminated preconditioning preconditioning preparation of 6 to 8 months old range-reared, recently weaned beef calves for entry into a feedlot and an intensive fattening program. Includes castration, dehorning and branding 3 weeks before and all vaccinations 2 weeks before weaning, and weaning 3 to 4 weeks requirements for components with nickel underplating, which cuts sample sizes for components using nickel as a mitigation practice and also reduces the test time required for these components. * Allowed an option for bias testing (when required) to be conducted in sockets. Joe Smetana, principle engineer, advanced technology for Alcatel and group chairman, said, "[T]here are a number of options for reducing the risk of tin whiskers, and we recognized the need for supplier feedback on the practicality of implementing the various approaches. Our goal was to ... [limit] testing requirements in an effort to save time and money but [while] still reducing the risk of tin whisker failures." Not everyone agrees that new efforts are needed, however. Several solutions were devised in Japan as much as 20 years ago; for details, see Jan Vardaman's column in Circuits Assembly (September 2004, pg. 22). The user group is comprised of 11 large manufacturers of electronics assemblies that agree that pure tin finishes (and other high-tin content lead-free alloy finishes) present a risk of tin whisker-related failures in electronics, particularly those demanding high reliability. |
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