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Tuesday, 02 June 2009 20:09

Emerging Technologies

“3D Integration – Future Perspectives”
Authors: M. Juergen Wolf, Peter Ramm, and Herbert Reichl; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: Advanced system-in-package (SiP) approaches explore the third dimension, which results in complex system architectures that require, besides new technologies and improved materials, adequate system design tools and reliability models. One promising approach is 3-D packaging, which involves a set of different integration approaches, including stacked packages, silicon interposers with through silicon vias (TSV), and embedded technologies. The paper highlights future system and potential technical solutions. (SMTA Pan Pac Symposium, February 2009)

“Longitudinal Unzipping of Carbon Nanotubes to Form Graphene Nanoribbons”
Authors: Dmitry V. Kosynkin, Amanda L. Higginbotham, Alexander Sinitskii, Jay R. Lomeda, Ayrat Dimiev, B. Katherine Price and James M. Tour; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstracts: Graphene, or single-layered graphite, with its high crystallinity and interesting semimetal electronic properties, has emerged as an exciting two-dimensional material showing great promise for nanoscale device fabrication. Thin, elongated strips of graphene that possess straight edges, termed graphene ribbons, gradually transform from semiconductors to semimetals as their width increases, and represent a particularly versatile variety of graphene. Several lithographic, chemical and synthetic procedures are known to produce microscopic samples of graphene nanoribbons, and one chemical vapor deposition process has successfully produced macroscopic quantities of nanoribbons at 950°C. This paper describes a simple solution-based oxidative process for producing a nearly 100% yield of nanoribbon structures by lengthwise cutting and unraveling of multiwalled carbon nanotube (MWCNT) sidewalls. Although oxidative shortening of MWCNTs has previously been achieved, lengthwise cutting is hitherto unreported. Ribbon structures with high water solubility are obtained. Subsequent chemical reduction of the nanoribbons from MWCNTs results in restoration of electrical conductivity. These early results affording nanoribbons could eventually lead to applications in fields of electronics and composite materials where bulk quantities of nanoribbons are required. (Nature, April 2009)

Lead-Free Assembly

“Lead-Free Assembly of Server Class PCBAs: Qualification Trial Results”
Authors: Matthew Kelly, Marie Cole, Jim Wilcox and David Braun; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: This paper reports the reliability testing results of a Pb-free assembly qualification trial on a midrange complexity, high-reliability assemblies sourced with three different PCB surface finishes. Reported results include electrical functionality through accelerated thermal cycling, isothermal high-temperature storage, as well as combination shock/vibration/ATC testing. Mechanical four-point bend test results and implications will be discussed. Construction analyses of various interconnect technologies are also included. Through continued product vehicle study, the capability of Pb-free processing is being systematically assessed for the extension of its applicability to higher complexity assemblies. (SMTA Pan Pac Symposium, February 2009)

Rework

“Column Grid Array Rework for High Reliability”
Authors: Atul C. Mehta and Charles C. Bodie; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: The most complex printed wiring board assembly used by the next MARS Rover project was chosen as the test vehicle, and modified to provide a daisy chain pattern. Nonfunctional 624-pin CGA packages with internal daisy-chained matching the pattern on the PWB were procured. The combination of the modified PWB and the daisy-chain packages enables continuity measurements of every soldered contact during subsequent testing and thermal cycling. Several test vehicles were assembled, reworked and then thermal-cycled to assess solder-joint and board material reliability, including pads and traces near the CGA. Removal and replacement of CGA-packaged parts from densely populated assemblies can be done, but require care in the selection of reflow profiles and process procedures. Solder joint reliability of the reworked assemblies is excellent and far exceeds the three-times mission lifetime required by NASA specifications. The major danger appears to be in the solder mask being overstressed and damaged in the cleanup after removal of the defective part. This danger is exacerbated by the presence of conformal coatings under the part. Pad lifting was not experienced, except for one incident that was easily repaired because only the corner of the pad detached from the PWB. Adjacent parts do not experience temperatures much above those normally reached during vapor phase reflow. The solder joints of those parts reach reflow temperatures and easily can be displaced with any disturbance. To err on the side of caution, it was decided to replace small discrete components within 0.5" of the CGA, and to remove expensive, long lead-time parts within this zone before rework and replace them after rework. (SMTA Pan Pac Symposium, February 2009)

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.

 

Columns

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For the first time in years we see parity in the Eastern US among EMS factories from Asia, Mexico and the US. This EMS market condition will permit American OEMs (the EMS industry refers to OEMs as customers) to have more EMS pathways to choose from. Now more than ever, such EMS assignments will require deeper investigation relating to the OEMs’ evaluation of manufacturing strategies.

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The Human Touch

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Circuits Disassembly: Materials Characterization and Failure Analysis

A systematic approach to nonconventional methods of encapsulant removal.

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