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"The Challenges of LGA Server Socket Trends"

Author: Bob McHugh;

Abstract: The high-end server market presents several manufacturing and technical challenges to socket manufacturers. Among the five notable trends: 1) Lower contact resistance. Contact resistance has a negative impact on current carrying capability and leads to higher socket operating temperatures. Given space constraints, the best approach to lowering contact resistance is by selecting materials with higher electrical conductivity. However, the tradeoff to higher conductivity materials is reduced mechanical performance. 2) Higher pin counts coupled with a need to maintain or lower socket loading force. Larger loading forces impact mechanical integrity and create ergonomic challenges. 3) Contacts with shorter electrical paths. As server frequencies increase, signal becomes more sensitive to noise. Reducing the seating plane height forces a shorter contact signal path and reduces the potential for noise in the circuit. 4) Higher contact density. The need for maintaining legacy real estate requirements along with the need for higher pin-counts results in the need for contact pitch reduction. S) Robotic assembly lines. This paper discusses challenges and some potential solutions for each of these trends. (SMTA Pan Pac Symposium, January 2013)

Printed Electronics

"Design of Printed Transistor Circuits for Printed Sensors"

Author: David Schwartz, Ph.D.;

Abstract: As printed transistor and sensor technologies advance, their integration into complex electronics systems becomes possible. Electronics design of such systems requires a systematic approach to simulation and design that takes into account the distinct challenges and opportunities presented by printed devices. An approach to circuit design and modeling in the context of building sensor systems based on an inkjet printed organic TFT process. (2013 Flexible & Printed Electronics Conference & Exhibition, January 2013)

Solder Joint Reliability

"Enhancing the Ductility of Sn-Ag-Cu Lead-Free Solder Joints by Addition of Compliant Intermetallics"

Authors: Huxiao Xie, Ph.D., and N. Chawla

Abstract: Sn-rich Pb-free solders containing rare-earth elements have been shown to exhibit desirable attributes of microstructural refinement and enhanced ductility relative to conventional Sn-3.9Ag-0.7Cu Pb-free solder, due to the unique mechanical properties of RE-Sn intermetallics. However, the roles of soft intermetallic phase in the enhanced ductility of Pb-free solder need to be further investigated. In this paper, Ca and Mn were selected as doping elements for SAC solder. The mechanical properties of CaSn and MnSn intermetallics as a function of indentation depth were measured by nanoindentation using the continuous stiffness method. The microstructure and mechanical properties of as-reflowed Ca- and Mn-containing SAC solder joints were studied and compared with those of conventional SAC and RE-containing solder joints. It is shown that soft intermetallics result in higher ductility in Pb-free solders. (Journal of Electronic Materials, March 2013)

"Mechanisms of Creep Deformation in Pure Sn Solder Joints"

Authors: K. 0. Lee, J. W. Morris Jr., and Fay Hua;

Abstract: The work reported here concerns the creep of pure Sn solder joints with Cu metallization (CullSnllCu). Steady-state creep tests in shear are combined with electron backscatter diffraction (EBSD) analysis. of the evolution of the microstructure during creep to clarify the deformation mechanism and the nature of the microstructural evolution. The creep behavior of the joint changes significantly with temperature. At low temperature (65[degrees]C), two distinct creep mechanisms are observed. Low-stress creep is apparently dominated by grain boundary sliding, as evidenced by the low stress exponent (n [approximately equal to] 4), low activation energy (Q [approximately equal to] 42 kJ/mole), and significant grain rotation during creep. High-stress creep is dominated by hulk deformation processes, evidenced by a high stress exponent (n [approximately equal to] 9), an activation energy like that for bulk diffusion (Q [approximately equal to] 70 kJ/mole), and a relatively fixed microstructure. At high temperature, all aspects of its behavior are consistent with deformation by bulk creep mechanisms; the stress exponent and activation energy are high (n [approximately equal to] 5 to 7, Q [approximately equal to] 96 kJ/mole), and despite significant grain coarsening, the microstructure retains (and strengthens) a fixed [001] texture. The results suggest that a "segmented" constitutive equation of Dorn type is most suitable for the low-temperature behavior, while a "hyperbolic" constitutive equation may be preferable at high temperature. (Journal of Electronic Materials, March 2013)

This column provides abstracts from recent industry conferences and company white papers. Our goal is to provide an added opportunity for readers to keep abreast of technology and business trends.
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Publication:Printed Circuit Design & Fab
Date:Mar 1, 2013
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