Circuits Assembly - December 2007 - (Page 48)

Technical Abstracts In Case You Missed It Environmental Compliance Eight Simple Steps to Convert EU RoHS to China RoHS Author: Roland Sommer, rsommer@rohs-international.com. Abstract: China RoHS is significantly different from EU RoHS; however, great leverage can be gained. The six hazardous substances are the same, and in most cases, so are the maximum concentration values. But, there are still traps for the unwary regarding some EU exemptions. While China RoHS does not require removal of the hazardous substances, it does require product and packaging labeling; a table in the users guide disclosing locations of any hazardous substances over the Chinese versions of the MCVs; and calculation of the environmentally friendly use period. These requirements are different from EU RoHS. Selective Soldering “Pb-Free Selective Soldering Process Optimization” Authors: Elavarasan T. Pannerselvam and S. Manian Ramkumar; smrmet@rit.edu. Abstract: Selective soldering process parameter effects such as solder pot temperature, preheat dwell, nozzle size, and feed rate of flux and solder application on solder joint formation are investigated. Design of experiments (DoE) was performed to investigate and identify key process parameters that influence the selective soldering process. SN100C (Sn/Cu/Ni + Ge) Pb-free solder alloy was used for this study. The investigation used a test vehicle containing a 16-pin DIP component, an axial component, and a radial component. Assembled boards were visually inspected per IPC-A610D for solder joint defects. Cross-section analysis was performed to observe through-hole fill. Among the selective soldering process parameters, solder pot temperature was found to be statistically significant. (SMTA International, October 2007) Solder Joint Reliability “Methodology for Evaluating Data For ‘Reverse Compatibility’ of Solder Joints” Authors: Bill Russell, Dennis Fritz and Gary S. Latta; wrussell@raytheon.com. Abstract: A large database of information was assembled from publicly available data on mixed SnPb and Pb-free solder assembly. Methodology was developed for comparing information sources by analyzing Weibull reliability charts for data consistency. From these preliminary results, it appears the N10, the number of cycles to 10 percent failures, is lower for solder joints formed from Pb-free alloys than joints formed from SnPb. In fact, the lifespan of lead-free alloys may only be one-quarter that of SnPb solders (vibration) to one-half (thermal cycling). These estimates may be optimistic because, in some cases, the SnPb joints had too few failures to estimate N10. Reworked solder joints fail even more quickly, having perhaps one-fifth the lifespan. Reworked joints appear most sensitive to vibration effects. During vibration, the board geometry does appear to influence resonance frequency and resulting physical deflections. Therefore, actual vibration levels differ for components in different locations on the board. Components at different points on the same board may be subjected to very different conditions. The calculated strain levels appear to provide some useful information in predicting component reliability. To judge the likely fatigue life of a component in a given application, some estimate of actual vibration level is essential. Most reports do not take time to perform the required analysis. The data on the reliability of reworked solder joints, especially on 140 Tg boards used in legacy equipment, are very thin. (SMTA International, October 2007) Substrates “Twisted Wire Interconnects: An Alternative to Multilayer Board Construction For High Component Density Printed Circuit Board Assemblies” Authors: Steve Garcia, Randy Boudreaux and Tom Borkes; jeffer2@earthlink.net. Abstract: High layer count board designs with components on both sides, requiring blind and buried via interlayer connecting, are replaced with a series of simple double-sided boards jointed using twisted wire interconnects – the TWI effectively replacing the traditional plated-through via holes used in multilayer designs. The paper demonstrates that a geometric increase in component density is achieved as TWI construction replaces higher layer count laminates. When an n-layer board is designed (i.e., n/2 plies laminated together) only two surfaces – the laminate top and bottom – are available for component attachment, regardless of layer count. Replacing this traditional design with a TWI assembly produces n surfaces for component attachment. Physical, mechanical and electrical design aspects of TWI are examined, as are TWI assembly processes. A comparative simplified modal analysis was done between a traditional multilayer board and equivalent TWI assembly. The TWI natural frequency was about seven times higher than the multilayer board. In practice, this results in lower solder joint strains and corresponding stresses. Performing a resonance dwell and subjecting assemblies to two MILSTD-810F random vibration environments – general integrity and jet aircraft, provided additional evidence of TWI mechanical robustness. (SMTA International, October 2007) CIRCUITS ASSEMBLY provides abstracts of papers from recent industry conferences and company white papers. With the amount of information increasing, our goal is to provide an added opportunity for readers to keep abreast of technology and business trends. 48 Circuits Assembly DECEMBER 2007 circuitsassembly.com http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - December 2007

Circuits Assembly - December 2007 Contents Caveat Lector Industry News Market Watch Talking Heads Global Sourcing Screen Printing Better Manufacturing Metalization Options for COB Assembly A Test Comparison of SAC and Non-SAC Pb-Free Solders An A-to-Z Guide to X-Ray Inspection BEST: A ‘Funky Chicken’ with an EMS Niche Tech Tips Wave Soldering Process Doctor Pb-Free Lessons Learned Getting Lean Eastern Approaches Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - December 2007

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