NIST COLLABORATES WITH NEMI ON STANDARDS PROJECT FOR LEAD-FREE SOLDERS.Tin-lead (Sn-Pb) solder has been used extensively as an electrodeposited surface finish for component contacts/leads in the electronics industry because such coatings provide excellent solderability, ductility ductility, ability of a metal to plastically deform without breaking or fracturing, with the cohesion between the molecules remaining sufficient to hold them together (see adhesion and cohesion). Ductility is important in wire drawing and sheet stamping. , electrical conductivity and corrosion resistance. The codeposition of Pb and Sn has been found to be effective in retarding Sn whisker growth and hence, has been the industry standard for over 20 years. In the absence of Pb, whiskers See metal whiskers. tend to grow spontaneously from electrodeposited Sn films, which can lead to electrical short circuits and device failure. Now that lead-free solder alloys have been introduced, electronic manufacturers are seeking a surface finish technology that will prevent Sn whisker growth without the use of Pb. Researchers at NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. are working to identify the basic mechanisms of Sn whisker growth by systematically studying correlations between deposit microstructure mi·cro·struc·ture n. The structure of an organism or object as revealed through microscopic examination. microstructure Noun a structure on a microscopic scale, such as that of a metal or a cell , whisker formation and electrodeposition e·lec·tro·de·pos·it tr.v. e·lec·tro·de·pos·it·ed, e·lec·tro·de·pos·it·ing, e·lec·tro·de·pos·its To deposit (a dissolved or suspended substance) on an electrode by electrolysis. n. The substance so deposited. parameters. For example, Sn-Cu solder has been mentioned as a possible replacement for Sn-Pb; however the NIST team has recently found that the addition of [Cu.sup.2+] to the Sn plating bath actually increases the probability and the speed at which whiskers form. Gaining a fundamental understanding of the whisker growth mechanism is required to help eliminate the problem and to develop a reliable test method for predicting whisker growth which the microelectronics industry requires. Towards this end, NIST is participating in a new 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 standards development project to help develop a robust test method for predicting whisker growth for industrial surface finish systems. |
|
||||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion