Extending the Fatigue Life of Solder Grid Array (SGA) Electronic Packages

[+] Author and Article Information
Michael C. Larson

Department of Mechanical Engineering, Tulane University, New Orleans, LA 70118-5674e-mail: larson@tulane.edu

Melody A. Verges

Department of Mechanical Engineering, University of New Orleans, New Orleans, LA 70148

J. Electron. Packag 125(1), 18-23 (Mar 14, 2003) (6 pages) doi:10.1115/1.1520430 History: Received December 03, 2001; Online March 14, 2003
Copyright © 2003 by ASME
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Schematic of a typical SGA package.
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A schematic of a row of solder interconnects being deformed as a result of a change in temperature when there is a disparity between the thermal expansion coefficient of the package, αp, and the PWB, αb. (a) The original shapes of the interconnects at some initial temperature, T0. (b) The deformed shapes of the interconnects at some temperature, T1.
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An SGA interconnect showing one possible failure mode: a fatigue crack paralleling the solder/chip carrier interface
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Schematic representations of the shear and normal stress variance with time and the change in mode-I and mode-II stress intensity factors with respect to crack advance with a superimposed tension across the crack faces
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Schematic representations of the friction-reduced shear stress with time and the change in mode-II stress intensity factor with crack advance with a superimposed compression across the crack faces
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Relative life curves for an applied strain up to 0.002. For example, a crack in an interconnect under compression lying on the curve labeled “2” would require twice as many cycles to reach a particular length than would a crack in the same interconnect without the imposed compression.
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Parameters bearing on the nominal shear strain in each interconnect: the temperature variation, ΔT, thermal expansion coefficients of the PWB, αb, and package, αp, the solder shear modulus, G, internal friction coefficient, μ, the distance of an interconnect from the neutral point (the center), L, the pad radius, r, the pitch, p, and stand-off height, h
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The nominal axial stresses in the solder interconnects and the underfill with the corresponding extension or reduction in the life of the interconnect which experiences the maximum shear strain. The values represent a rule of mixtures estimation corresponding to the particular illustrative geometry described in the text.




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