On The Road To Lead Free -- Several studies report benefits of using lead-free solders, but certain technical issues must be considered before lead free can be implemented in electronics assembly.Since the recognition of lead's potential health hazards, its uses have been increasingly regulated. In consumer electronics, the adoption of lead-free electronics assembly is progressing largely in response to proposed legislation such as the directive on Waste in Electrical and Electronic Equipment (WEEE WEEE Waste from Electric and Electronic Equipment (directive) WEEE Waste Electrical and Electronics Equipment WEEE Waste Electrical and Electronic Equipment ) in Europe1 and many laws in Japan.2 Many technical issues must be overcome as part of the lead-free process implementation. Some will argue that we should not change from current eutectic soldering because of these unanswered issues. However, investigations are finding that lead-free technology may be an improvement in terms of reliability and manufacturing waste disposal. Many questions arise concerning the implementation of lead-free processing, ranging from the definition of lead free to concerns about its implementation costs. Information used for clarification in this article includes test results from assemblies using lead-free plastic ball grid arrays “BGA” redirects here. For other uses, see BGA (disambiguation). A ball grid array (BGA) is a type of surface-mount packaging used for integrated circuits. (PBGAs) and from off-the-shelf components combined with lead-free 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. . Technical Issues The foremost issue is how lead-free assemblies will perform when compared to eutectic solder assemblies that are industry standards. Can the same performance and reliability be expected, and can the lifetime of the assembly be predicted? Will lead-free solders have limited application, or can they be used wherever eutectic solders are now used? As additional data are published, the benefits of lead-free solder appear to exceed the requirements of proposed regulations. Evaluations of toxicological risk, economic factors, physical properties and reliability have been conducted for lead-free solders,3-8 but variations in reliability due to different board surface finishes must also be considered. Technical issues also include the modifications of solder joint metallurgy due to differences in component termination metallurgy and the higher processing temperatures required for lead-free alloys. Heat damage to boards and components, rework re·work tr.v. re·worked, re·work·ing, re·works 1. To work over again; revise. 2. To subject to a repeated or new process. n. process complications and end-of-life metal reclamation must also be considered. Board surface finish can have two most likely effects on the solder joint. First, the interfacial bond strength of the solder joints can vary depending on the type of intermetallic combinations that form at the pad interface. Second, the dissolution of the surface finish metallurgies can significantly alter the 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 and physical characteristics of the solder joints. Uniform component termination metallurgies can improve reliability predictions for solder joints formed from the combination of metallurgies in the paste, board surface finish and component terminations. Without such a consensus, reliability predictions will be difficult. Higher reflow (1) The process of heating and melting the solder that has been screen printed onto a printed circuit board in order to bond chips and other components to the board. Surface mount chips (SMT) use the reflow method. Contrast with wave soldering. See also reflowable text. temperatures increase the dissolution rates, thereby possibly increasing the percentages of termination and surface finish elements in the solder joints. For example, a nickel/gold (Ni/Au) board finish combined with gold termination on the component could exceed the threshold weight percent of gold in the solder joint (A3 percent).9 The weight percent limit for gold in lead-free solder joints is not precisely defined. Metallurgical interactions need not be feared. Superior low-cycle fatigue life of lead-contaminated samples over eutectic solders has been reported.10 With common terminations, the variability and associated concerns are reduced. The effects of oven temperatures up to 250 degrees C can vary from no effect to latent defects to outright failures. The latent defects become apparent only after increased field failure rates are reported. Also, a concern of increased moisture sensitivity due to faster ramp rates and higher reflow temperatures was reported.11,12 Board discoloration dis·col·or·a·tion n. 1. a. The act of discoloring. b. The condition of being discolored. 2. A discolored spot, smudge, or area; a stain. Noun 1. and increased warping have also been observed when using lead-free solder.13 However, shorter exposure times than those cited greatly improve results, without discoloration or material degradation. Inspection of the solder joints must also be considered as part of the evaluation of lead-free solders. Considerable learning will have to occur to establish standard inspection criteria due to decreases in wettability and the coarse surface finish of the solder joints, and the complexities introduced by the addition of other elements during the soldering process. Rework processes will require more training and development due to the changes in the properties of the solder by the additions of elements from the PWB (Printed Wiring Board) An alternate term for printed circuit board. See printed circuit board. and component terminations. These added elements can significantly alter the melting temperature Melting temperature may refer to:
Metal reclamation is another aspect of lead-free implementation. Discussions of cradle-to-grave ownership of products by their makers require evaluation of the recycling cost of the assembly. The processing required to remove each additional element from the assembly can be reduced substantially by selecting a particular solder alloy or components with common termination metallurgy. Initiating an early dialogue with reclamation service providers will help in the selection of lead-free alloys and board surface finishes. Lead-Free Assembly In a recent study, lead-free, 289 I/O (Input/Output) The transfer of data between the CPU and a peripheral device. Every transfer is an output from one device and an input to another. See PC input/output. I/O - Input/Output , daisy chained PBGAs were assembled on FR-4 boards with three different PWB surface finishes and tin/copper/silver (Sn/Cu/Ag) solder paste. The study examined the comparable reliability between eutectic and lead-free alloy processing. Specifically, the PBGA PBGA Plastic Ball Grid Array components were assembled on 1.15 mm (0.046 in.) thick FR-4, high-density microvia test boards using a peak reflow temperature below 245 degrees C. Both organic solderability preservative preservative Any of numerous chemical additives used to prevent or slow food spoilage caused by chemical changes (e.g., oxidation, mold growth) and maintain a fresh appearance and consistency. Antimycotics (e.g. (OSP (Online Service Provider) See online service. OSP - Optical Signal Processor ) and electroless nickel/immersion gold (Ni/Au) surface finishes on copper (Cu) were used to evaluate different board surface finishes combined with lead-free processing. After assembly, metallographic met·al·log·ra·phy n. The study of the structure of metals and alloys, especially by optical and electron microscopy and x-ray diffraction. met cross sections were prepared for comparison of tin/lead (Sn/Pb) and lead-free solder joints prior to testing. The solder joint formation and grain structure were examined. The observed differences in the pad coverage, size, and shape of Sn/Pb and Sn/Ag/Cu solder joints were minimal when the process is optimized. Temperature cycle tests were performed from -40 degrees C to 125 degrees C with 14-minute dwells at temperature extremities and with 3-minute transition periods. Testing continued to 1,600 cycles, and failures were documented using an event detector. Figure 1 shows equivalent performance of assemblies using lead-free solder on OSP and Ni/Au. Lead-free reliability was also equal to or better than the Sn/Pb control assemblies. These results are consistent with the results from other studies.14 The typical failure mode on both Sn/Pb and Sn/Ag/Cu assemblies, using both surface finishes, was cracks at the interface of the component and solder. Lead-free solder paste with lead-free component termination performed well in this application. Mixed Technology Mixed technology in this article refers to lead-free solder used with off-the-shelf component terminations currently available. These combinations were considered because, to date, only a few components have been qualified as lead-free compatible. Lead-containing terminations are common, and the effects of the various lead-free terminations when combined with lead-free solder are not well understood. Double-sided, 0.76 mm (0.030 in.) thick, FR-4 high-density microvia test boards, with a typical electroless nickel and immersion gold (Ni/Au) surface finish, were used, along with tin/silver/copper/antimony (Sn/Ag/Cu/Sb) solder paste. Microvias were present in many pads, but no interactions of via-in-pad versus non-via-in-pad were evaluated. Standard off-the-shelf components were selected to highlight the variety of metallurgies in mixed-technology solder joints. Components assembled included four area array packages: one microBGA with 46 I/O chip scale package A chip scale package (CSP) (sometimes, chip-scale package with a hyphen) is a type of integrated circuit chip carrier. According to the IPC, to qualify as chip scale, the package must have an area no greater than 1.2 times that of the die that is being packaged. (CSP (1) (Certified Systems Professional) An earlier award for successful completion of an ICCP examination in systems development. See ICCP. (2) (Commerce Service P ), one 48 I/O CSP, a flex-based 144 I/O and a laminate-based 64 I/O CSP. Three different leadless ceramic chip carriers (LCCCs) and three different plastic LCCs were used. Other components included 16- and 20-pin small outline integrated circuits Integrated circuits Miniature electronic circuits produced within and upon a single semiconductor crystal, usually silicon. Integrated circuits range in complexity from simple logic circuits and amplifiers, about 1/20 in. (1. (SOICs), various standard size chip capacitors and resistors down to 0402s, and three inductors with different size and orientation of the ceramic spools. Testing was performed after every 100 thermal cycles and after every two drops from a height of 1.5 m. Mixing lead-free technologies, a Ni/Au PWB surface finish and off-the-shelf components on the same board produced solder joints that varied in surface finish and metallurgical content.15 Most elements contained in the PWB pad or the component termination were found in cross sections of the solder joints. Mixing the lead-free and lead technologies can increase the difficulty of predicting the assembly's long-term reliability, but the final results were promising as compared to the eutectic control boards. Reflow profile Control samples using eutectic solder paste and the standard reflow profile were assembled, followed by the test boards using lead-free paste. Peak component temperature in the lead-free profile never exceeded 245 degrees C, far below the 260 degrees C maximum often stated as a requirement for lead-free processing. The lower temperature is consistent with results from other studies using lead-free flip chip A chip packaging technique in which the active area of the chip is "flipped over" facing downward. Instead of facing up and bonded to the package leads with wires from the outside edges of the chip, any surface area of the flip chip can be used for interconnection, which is typically done 16 and surface-mount components.14,17 Board discoloration and warps were not reported. Accordingly, lead-free assemblies can be processed without damage. Moisture sensitivity Lead-free processing typically requires increased ramp rates and a shorter overall oven profile to prevent drying of smaller solder paste deposits. Therefore, moisture exposure should be considered, and the reflow effects on boards should be examined for each application. In the mixed-technology application, popcorn cracks were found at initial test and inspection in 11 plastic encapsulated, 16-pin SOICs exposed to two lead-free reflow cycles. A 28-percent failure rate for lead-free processing versus a five-percent failure rate for the eutectic solder control boards indicates the effects of the lead-free reflow profile on moisture-sensitive components. Joint Electron Device Engineering Council (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 ) moisture sensitivity levels Moisture Sensitivity Level relates to the packaging and handling precautions for some semiconductors. The MSL is an electronic standard for the time period in which a moisture sensitive device can be exposed to ambient room conditions (approximately 30°C/60%RH). of current plastic components can decrease as much as two levels by using lead-free processing. Visual inspection of solder joints Many variations on the solder joint surfaces were noted. In general, variations on an assembly can range from the striated striated /stri·at·ed/ (stri´at-ed) having stripes or striae. striate, striated having streaks or striae, e.g. striate retinopathy. striate border see brush border. finish on a high gold content solder joint to the mottled mottled /mot·tled/ (mot´ld) marked by spots or blotches of different colors or shades. finish on a joint containing lead and bismuth bismuth (bĭz`məth) [Ger. Weisse Masse=white mass], metallic chemical element; symbol Bi; at. no. 83; at. wt. 208.9804; m.p. 271.3°C;; b.p. about 1,560°C;; sp. gr. 9.75 at 20°C;; valence +3 or +5. (Bi). A coarse finish is typical of many lead-free solder joints. Even with these variations, acceptable wetting angles can be achieved with a range of components. During drop testing, a complication was revealed for visual inspection. A line resembling a crack was first observed after three drop tests had been completed. The lines darkened dark·en v. dark·ened, dark·en·ing, dark·ens v.tr. 1. a. To make dark or darker. b. To give a darker hue to. 2. To fill with sadness; make gloomy. 3. as testing continued, but the joints did not fail. Figure 2 shows a resistor resistor, two-terminal electric circuit component that offers opposition to an electric current. Resistors are normally designed and operated so that, with varying levels of current, variations of their resistance values are negligible (see resistance). solder joint with the "discoloration" and surface voids that formed on the exterior of the solder. Visual inspection of field-returned systems may be complicated by false calls. Cross sections revealed the lines were not cracks. Variations in solder joint metallurgy Figure 3 shows a typical post-assembly LCCC LCCC Laramie County Community College (Cheyenne, WY, USA) LCCC Lehigh Carbon Community College LCCC Lorain County Community College (Elyria, Oh) LCCC Lancashire County Cricket Club solder joint formed with Ni/Au finish on the terminations. Numerous Au/Sn intermetallic needles were observed throughout the solder joint. Two zones separated by a Cu/Sn intermetallic layer were seen in post-assembly samples and after testing. An example is the LCCC solder joint in Figure 4. Near the surface of the termination is a zone containing approximately seven- to nine-percent gold content. The bulk solder zone has approximately five- to seven-percent gold content. Presumably pre·sum·a·ble adj. That can be presumed or taken for granted; reasonable as a supposition: presumable causes of the disaster. , the Cu/Sn layer began to form as the gold from the component surface and the board surface dissolved into the solder and was trapped between the "wave fronts" of Au/Sn intermetallic formations. Another extreme solder joint metallurgy (Figure 5) contains bismuth, silver, palladium (Pd) and platinum (Pt), in addition to the gold and copper present in smaller quantities in the tin matrix. This picture was taken after 24 drops. Other elements detected in the different solder joints included lead, iron (Fe), nickel, phosphorus (P), bismuth, copper, silver, gold, platinum, palladium, tungsten (W) and cobalt (Co). As mentioned, mixing the lead and lead-free technologies in the solder joint can increase the difficulty of predicting the assembly's long-term reliability, but the final result from this test shows promise. Failure mechanisms Figure 6 shows a LCCC solder joint after 24 drops. Although a distinct "discoloration" line was noted on the surface of the solder joint in visual inspection (Figure 2), it was not evident in the internal grain structure of the solder joints and no cracks were found. Thermal shock Thermal shock in mechanical models Thermal shock is the name given to cracking as a result of rapid temperature change. Glass and ceramic objects are particularly vulnerable to this form of failure, due to their low toughness, low thermal conductivity, and high testing provided similar results. Surface voids observed in Figure 6 were not found in the post-assembly solder joints. They are consequences of mechanical drop and thermal stresses. Figure 2 shows the darkened circular areas around the voids on the exterior surface of a stressed solder joint. Most of the fractures due to thermal shock were not in the solder but at interfaces of the layers in the component terminations. Figure 4 shows the initial separation of the barrier layers from the thick-film terminations subjected to thermal shock. No solder joint failures were detected as a result of drop testing. A few cracks were found propagating toward an open through the intermetallic layer on the PWB solder pad. Those cracks appear to be associated with the presence of voids in the joints. This conclusion was reached due to the absence of cracks in solder joints without voids. As expected, LCCCs were the first and the only components to fail in testing.18 Every failure in thermal cycling was traced to a LCCC on each test board. Cracked solder joints were easily identified by visual inspection in both lead-free and control samples. The eutectic Sn/Pb control boards showed the greatest damage to the LCCC solder joints, indicating earlier failures as compared to the lead-free solder joints. Cracks in the lead-free LCCC solder joints propagated through the high stress zone of the fillet fillet /fil·let/ (fil´et) 1. a loop, as of cord or tape, for making traction on the fetus. 2. in the nervous system, a long band of nerve fibers. fil·let n. 1. . The cracks followed the Au/Sn needles when they were aligned close to the propagation path, but they were often transgranular, following paths through the Au/Sn needles instead of beside them as is common in eutectic solders.19 The lack of a lead-rich zone around the needles eliminated a low resistance path that typically leads to premature failures in gold-rich Sn/Pb solders. Only one partial crack was found in an area array solder joint. This crack was located where the solder mask An insulating pattern applied to a printed circuit board that exposes only the areas to be soldered. dam across a dogbone trace contacts the solder joint. Contact between the solder and the high coefficient of thermal expansion coefficient of thermal expansion, n See expansion, thermal coefficient. of the solder mask likely induced the crack. Discussion The surface morphology of lead-free solder joints can be rough and mottled in contrast to the eutectic Sn/Pb joints. Intermetallics of Cu/Sn seemed to precipitate on the solder interfaces to the component and circuit board pads. This precipitation occurred on solder joints with and without lead content. No discoloration of the circuit boards was observed after two reflow profiles when compared to virgin circuit boards. Board warpage during reflow was minimal, and no assembly problems were noted. Moisture sensitive plastic packages are expected to be at greater risk to damage in reflow. Appropriate handling procedures are vital for successful assembly in the higher reflow temperatures. In the solder joints examined, Au/Sn intermetallics were found well dispersed in most solder joints. When lead was present in the mixed technology solder joints made with lead-free solder paste, the Au/Sn intermetallics were difficult to detect. Exceptions were noted on components with gold-coated terminations. In these solder joints, the Cu/Sn intermetallics were found in the region adjacent to the component, between a layer of solder with high gold concentration and the bulk of the solder joint with a lower gold concentration. Ag/Sn intermetallics were seen dispersed throughout most solder joints. The presence of tungsten, cobalt, nickel, platinum, palladium and iron in the bulk of some solder joints suggests dissolution and dispersion of termination metallurgies into the joint due to the high reflow temperature. The effects of these minor elements on the joint's physical properties (such as tensile strength tensile strength Ratio of the maximum load a material can support without fracture when being stretched to the original area of a cross section of the material. When stresses less than the tensile strength are removed, a material completely or partially returns to its , bulk modulus bulk modulus Numerical constant that describes the elastic properties of a solid or fluid under pressure from all sides. It is the ratio of the tensile strength or compressive force per unit surface area to the change in volume per unit volume of the solid or fluid and thus and creep behavior) are unclear, but the solder joints performed better than the eutectic control solder joints. The control samples assembled with Sn/Pb eutectic alloy eu·tec·tic alloy n. An alloy that is generally brittle, easily melted, and subject to tarnish and corrosion, used primarily in dental solders. solder paste experienced thermal shock failures earlier than those with lead-free solder paste, indicating superior performance of mixed technology lead-free assemblies. Also noteworthy is that the local coefficient of thermal expansion (CTE (Coefficient of Thermal Expansion) The difference between the way two materials expand when heat is applied. This is very critical when chips are mounted to printed circuit boards, because the silicon chip expands at a different rate than the plastic board. ) mismatch is less with lead-free alloys in comparison to eutectic Sn/Pb. Mechanical shock induced through drop testing did not produce any failures up to 24 drops. However, in the solder joints examined, cracks were more commonly found propagating in the solder joints containing voids. The cracks in these samples propagated through the Cu/Sn intermetallic formations on the surface of the pads and through the component termination layers. The presence of cracks in the component termination layers may be the result of the relatively greater strength of lead-free solders and could indicate new concern for investigation. Conclusion Lead-free assembly studies cited correspond to growing evidence showing benefits of using lead-free solder beyond simply meeting proposed environmental requirements. Technical issues that must be considered include: -Visual inspection of lead-free solder joints will be more complex than for eutectic solders. - JEDEC moisture sensitivity levels of current plastic components can decrease by as much as two levels through implementation of lead-free processing. -Metallurgical variations resulting from the combination of the lead-free solder paste, the component termination, and the board surface finish: - require further research to define if they are a reliability exposure or an improvement - may have different failure mechanisms than the eutectic Sn/Pb solders - may be more susceptible to early failures due to the presence of voids in the solder joint. -Common lead-free component terminations should be encouraged to improve reliability predictions for lead-free assemblies. Positive results for Sn/Ag/Cu solders from a growing number of sources include: -good solder joints at reflow temperatures below 245 degrees C without board and component damage -superior thermal cycling reliability over eutectic solders -improved mechanical drop reliability as compared to eutectic solder -longer survival of high gold-content solder joints than the eutectic control solder joints in thermal shock. Additional detailed metallurgical studies are required to understand the behavior of lead-free alloys under thermomechanical stresses. These studies should be undertaken to optimize the results for each particular application. Studies should be done not just to meet regulatory requirements, but to take advantage of the benefits of lead-free solder. --- Acknowledgments The authors would like to acknowledge: Gary Hung, Chuan Xia, Mervi Kulojarvi, Pilvi Vihervuori, Peter Leitel, Marshall Turman, Robert Champaign and Jody Roepsch. --- References 1. European Union European Union (EU), name given since the ratification (Nov., 1993) of the Treaty of European Union, or Maastricht Treaty, to the European Community . (2000). Directive of the European Parliament European Parliament, a branch of the governing body of the European Union (EU). It convenes on a monthly basis in Strasbourg, France; most meetings of the separate parliamentary committees are held in Brussels, Belgium, and its Secretariat is located in Luxembourg. and of the Council on Waste Electrical and Electronic Equipment. Brussels, Belgium, 13.6.2000 2. Perlewitz, H. (1998). Disassembly dis·as·sem·ble v. dis·as·sem·bled, dis·as·sem·bling, dis·as·sem·bles v.tr. To take apart: disassemble a toaster. v.intr. 1. and Recycling of Durable and Consumer Goods consumer goods Any tangible commodity purchased by households to satisfy their wants and needs. Consumer goods may be durable or nondurable. Durable goods (e.g., autos, furniture, and appliances) have a significant life span, often defined as three years or more, and in Japan-Present Condition and Trends of R&D Activities. Tokyo, Japan. October, Holger.Perlewitz@iwf-mt.tu-gerlin.de. 3. NCMS NCMS National Center for Manufacturing Sciences NCMS National Classification Management Society NCMS National Compliance Management Services, Inc. NCMS North Carolina Masters Swimming NCMS North Canton Middle School (North Canton, OH) . (1997). Lead-Free Solder Project Final Report, Report 0401RE96. Ann Arbor, Michigan  “Ann Arbor” redirects here. For other uses, see Ann Arbor (disambiguation). Ann Arbor is a city in the U.S. state of Michigan and the county seat of Washtenaw County. : National Center for Manufacturing Sciences. August. 4. Laine-Ylijoki, T., et al. (1996). Development and Validation of a Lead-Free Alloy for Solder Paste Applications. International Conference on Electronic Assembly: Material and Process Challenges, Atlanta, GA, May 29-31. 5. Grandi, G., et al. (1999). Intermetallic Compounds Intermetallic compounds Materials composed of two or more types of metal atoms, which exist as homogeneous, composite substances and differ discontinuously in structure from that of the constituent metals. They are also called, preferably, intermetallic phases. In Lead-free Soldering. Tampere University of Technology Tampere University of Technology (TUT) (Finnish: Tampereen teknillinen yliopisto (TTY) ) is the second-largest of the universities in engineering sciences in Finland. The university is located in Hervanta, a suburb of Tampere. , Report #10. 6. Peng, W., et al. (2000). A Literature Review on Potential Lead-Free Solder Systems. Helsinki University of Technology TKK redirects here. For other uses, see TKK (disambiguation). Helsinki University of Technology is not to be confused with University of Helsinki. Helsinki University of Technology (TKK) (Finnish: Teknillinen korkeakoulu; Swedish: Tekniska högskolan , report series HUT-EPT-1 2000. 7. Zeng, K., et al. (2000). Formation of Intermetallic Compounds in Solder Joints and Its Effects on Joint Reliability. Helsinki University of Technology, report series HUT-EPT-2 2000. 8.Kato, R. (1998). Lead Free Solder for Environmental Protection. Sinju Metal Industry Co. Ltd., R&D Report, May. 9. Glazer, J., et al. (1999). Effect of Au on the Reliability of Fine Pitch Surface Mount Solder Joints. Journal of Surface Mount Technology, pp. 15-27, October. 10. Whang, J., and Guo, Z. (2001, January/February). Effects of Pb contamination on the material properties of Sn/Au/Cu solder. Chip Scale Review, Vol. 5, No. 1, pp. 92-94. 11. Whitten, G. (2000). Lead-free Solder Implementation for Automotive Electronics. ECTC ECTC Electronic Components and Technology Conference ECTC Erosion Control Technology Council ECTC Earth Commission for Thermostatic Control (from environmentalist book The Weather Makers) ECTC Expected Cost to Company 2000, Las Vegas Las Vegas (läs vā`gəs), city (1990 pop. 258,295), seat of Clark co., S Nev.; inc. 1911. It is the largest city in Nevada and the center of one of the fastest-growing urban areas in the United States. , NV. 12. Kwoka, M., and Obrien, G. (2000). Lead-Free Components FOCUS Group Evaluation -Status Report 1. 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. Works 2000, Sept. 9-14, Miami, FL. 13. Yunus, M. and Srihari, K. (1999). Reflow Profile Development For Lead-Free Solders. Universal Instruments Consortium, technical report, September. 14. Bartelo, J., et al. (2001). Thermomechanical Fatigue Behavior of Selected Lead-free Solders. APEX Proceedings, Jan. 14-18, pp. LF2-2. 15. Dunford, S., et al. (2000). Metallurgical and Reliability Aspects of Lead-free Mixed Technology Electronic Assembly for Mobile Communication Products. IPC Works 2000, Sept. 9-14, Miami, FL. 16. Tonapi, S., et al. (2001). Effects of Flux and Reflow Parameters on Lead-Free Flip Chip Assembly. APEX Proceedings, Jan. 14-18, pp. AT5-2. 17. Shina, S., et al. (2001). Selecting Material and Process Parameters for Lead-free 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 Soldering Using Design of Experiments. APEX Proceedings. Jan. 14-18, pp. LF1-1. 18. NCMS. Lead-Free Solder Project Final Report, Report 0401RE96. Ann Arbor, Michigan: National Center for Manufacturing Sciences. 19. Chase, L., et al. (2000). Comparison of Ag, Ni/Au, and Solder PWB Surface Finishes on The Second Level Reliability of Fine Pitch Area Array Assemblies. SMTA SMTA Surface Mount Technology Association SMTA Standard Material Transfer Agreement SMTA Subordinate Message Transfer Agent SMTA Sewing Machine Trade Association (UK) SMTA Sekolah Menengah Tingkat Atas International, Sept 24-28. --- Steven O. Dunford is a research engineer, e-mail: steven.dunford@nokia.com, and Dr. Puligandla Viswanadham is a research manager, e-mail: viswam.puligandla@nokia.com, both in Irving, TX, and Pekka Rautila is manager of the production technology lab; Salo, Finland Salo (IPA: [ˈsɑlo]) is a town and municipality of Finland. It is located in the province of Western Finland and is part of the Finland Proper region. ; all with Nokia Mobile Phones Inc. Copyright [copyright] 2001 CMP CMP (cytidine monophosphate): see cytosine. (1) (CMP Media LLC, Manhasset, NY, www.cmp.com) Part of United Business Media, CMP is a leading integrated media company that offers a wide variety of publications and services in the information Media LLC (Logical Link Control) See "LANs" under data link protocol. LLC - Logical Link Control |
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