Is the supply chain ready for RoHS? Common materials and the availability of RoHS-compliant versions.Ed: For the full article, please see www.pcdandm.com. MANUFACTURERS HAVE MADE significant investments in new processes that will eliminate substances banned under the EU's RoHS Directive. But they must also be assured of a strong supply chain that can provide sufficient replacement materials. Many systems elements will need to be RoHS-compliant, including cables, connectors, plastics and enclosure sheet metal. Printed circuit boards. Manufacturers are concerned about the compatibility of PCB PCB: see polychlorinated biphenyl. PCB in full polychlorinated biphenyl Any of a class of highly stable organic compounds prepared by the reaction of chlorine with biphenyl, a two-ring compound. materials with lead-free soldering soldering Process that uses metal alloys with low melting points to join metallic surfaces without melting them. Tin-lead solders, once widely used in the electrical and plumbing industries, are now replaced by lead-free alloys. temperatures of 240 to 260 [degrees]C. Some high-temperature materials High-temperature materials A metal or alloy which serves above about 1000°F (540°C). More specifically, the materials which operate at such temperatures consist principally of some stainless steels, superalloys, refractory metals, and certain ceramic are becoming available in production quantities, but availability will be constrained con·strain tr.v. con·strained, con·strain·ing, con·strains 1. To compel by physical, moral, or circumstantial force; oblige: felt constrained to object. See Synonyms at force. 2. through 2006. All major PCB manufacturers currently offer some version of a RoHS-compliant board finish. Compliant OSPs are commonly available, but require a high degree of process control for high-yield soldering. Immersion tin and silver finishes are readily available. Cable insulation materials. Cadmium cadmium (kăd`mēəm) [from cadmia, Lat. for calamine, with which cadmium is found associated], metallic chemical element; symbol Cd; at. no. 48; at. wt. 112.41; m.p. 321°C;; b.p. 765°C;; sp. gr. 8. , hexavalent chromium Hexavalent chromium or Cr(VI) compounds are those which contain the element chromium in the +6 oxidation state. Chromates are often used as pigments for photography, and in pyrotechnics, dyes, paints, inks, and plastics. and lead compounds are often found in polyvinylchloride, which is used for cable insulation. Major cable suppliers are implementing substitute materials, such as titanium, for RoHS-compliant cables. Connector materials. A pure tin finish meets RoHS requirements, but lead removal increases the potential for tin whisker formation and growth. The connector industry is generally moving to SnNi plating, which mitigates tin whiskers See metal whiskers. . (1) No supply problems should arise. Electrical components. Plated through-hole devices typically use SnPb plating over a copper-plated steel wire. Pure tin plating is usually of little concern for PTH PTH abbr. parathyroid hormone Parathyroid hormone (PTH) A chemical substance produced by the parathyroid glands. This hormone is a major element in regulating calcium in the body. devices because of the relatively wide (>1 mm) spacing between adjacent leads. Wire wound resistors, some capacitors and some LEDs are available with PTH connections. Obtaining RoHS-compliant PTH connection devices by the end of 2005 should not be a problem. SMT (1) (Surface Mount Technology) See surface mount. (2) (Station ManagemenT) An FDDI network management protocol that provides direct management. Only one node requires the software. SMT - Station Management lead-frame manufacturers have historically used SnPb as a finish coating, and many intend to use a pure tin replacement finish. Tin whiskers are a major reliability concern for components with tight lead-frame spacing (<1 mm) and high-reliability system manufacturers are requiring suppliers to implement one of several whisker mitigation strategies for lead-frame components with tight spacing. (2) With the exception of some legacy products, RoHS-compliant SMDs should be available. BGAs with high lead content (>85%) are RoHS-exempt for reliability purposes. However, eutectic SnPb BGAs will have to remove lead. All BGA (Ball Grid Array) A popular surface mount chip package that uses a grid of solder balls as its connectors. Available in plastic and ceramic varieties, BGA is noted for its compact size, high lead count and low inductance, which allows lower voltages to be used. component manufacturers will provide lead-free BGAs by the end of this year. Server and storage products are exempted from RoHS until 2008. But availability of SnPb BGA components will be problematic because most manufacturers are switching production to lead-free BGAs for high-volume commodities that are not exempt. Mixing lead-free solder balls In BGA chip packages, it is the tiny globe of solder that provides the contact between the chip package and the printed circuit board. Also called a "solder bump." See BGA. with SnPb solder paste Solder paste (or solder cream) is a mix of small solder particles and flux. It is used extensively in the automated soldering processes wave soldering and reflow soldering. causes reliability degradation. When SnPb BGA balls are no longer available, manufacturers must decide whether to use lead-free solder solder (sŏd`ər), metal alloy used in the molten state as a metallic binder. The type of solder to be used is determined by the metals to be united. Soft solders are commonly composed of lead and tin and have low melting points. Hard solders (i. attach or stay with SnPb solder. Sheet and bulk metal. All electronic hardware needs a mechanical enclosure, meaning that sheet steel must be RoHS-compliant. Additional internal mechanical hardware use sheet steel and must also be compliant. Sheet steel is typically purchased with a coating, most commonly hexavalent chromium. Since RoHS regulations require hexavalent chromium concentrations in the coating be <1000 ppm, most system designers have eliminated it as a steel finishing process. See TABLE 1 for a list of sheet steels common to electronic enclosures (and their coatings). REFERENCES (1.) G.T. Galyon and R. Gedney, "Avoiding Tin Whisker Reliability Problems," Circuits Assembly, August 2004, pp. 26-32. (2.) Recommendations on Lead-Free Finishes for Components Used in High-Reliability Products (updated May 2005), iNEMI Tin Whisker User Group. http://thor.inemi.org/webdownload/projects/ese/tin_whiskers/ User_Group_mitigation_May05.pdf. GEORGE GALYON is senior technical staff member at IBM (International Business Machines Corporation, Armonk, NY, www.ibm.com) The world's largest computer company. IBM's product lines include the S/390 mainframes (zSeries), AS/400 midrange business systems (iSeries), RS/6000 workstations and servers (pSeries), Intel-based servers (xSeries) (ibm.com) and chairs the iNEMITin Whisker Modeling Project; galyon@us.ibm.com. GLENN (WOODY) SELLERS is senior engineer with IBM. RON GEDNEY consults on iNEMI's Pb-free and tin whisker projects.
TABLE 1. Availability of RoHS-Compliant Sheet Steel Finishes
QUALIFIED SHEET STEEL FINISHES
SALT SPRAY (1 M[ohm] SHEET CONDUCTIVITY)
REQUIREMENT (>24 HR. SALT SPRAY) AVAILABILITY
24 hrs. Zn with trivalent passivation Available in U.S. and
Galvanneal E-coat Europe Available
(a painted Zn) globally
48 hrs. Zn with trivalent passivation Available in U.S. and
Europe
72 hrs. E-Gal Zn with anti-fingerprint Available from Japanese
(AFP) sources
96 hrs. 3 pm of electroless nickel Available globally
105 hrs. Aluminized steel 5 [micro]m Available in U.S. only
of electroless nickel Available globally
As of June 2005. Note: Steel is purchased by its ability to withstand a
salt spray test.
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