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RESEARCH PAPERS

Characterization and Modeling of Printed Wiring Board Warpage and its Effect on LGA Separable Interconnects

[+] Author and Article Information
J. Cepeda-Rizo

Department of Mechanical and Aerospace Engineering,  California State University, Long Beach, California

Hsien-Yang Yeh1

Department of Mechanical and Aerospace Engineering,  California State University, Long Beach, California

N. Teneketges

Enabling Technologies—Packaging Technology,  Teradyne Inc., Agoura Hills, California

1

Corresponding author; electronic address: hyyeh@csulb.edu

J. Electron. Packag 127(2), 178-184 (Sep 30, 2004) (7 pages) doi:10.1115/1.1898339 History: Received September 16, 2003; Revised September 30, 2004

The paper presents a study on printed wiring board (PWB) warpage caused by the mechanical fastening of separable interconnects, known as land grid array (LGA) package assemblies. Out-of-plane displacement of the PWB were measured and characterized, as well as force-per-pin values of the LGA, and correlations were made between the two. Classical laminate theory was utilized to describe the warpage behavior of the assembly and a model was presented to solve the out-of-plane displacements. An overall assessment of the assembly was made and compared to the mechanical specification of the LGA.

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Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 8

PWB warpage by Levy’s approximation predicting the reverse saddle warpage of the board at the LGA area. All dimensions shown above are in inches.

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Figure 9

Comparison of both Navier and Levy predicted approximations vs the measured values. The horizontal axis represents the distance from the center of the plate along the x axis.

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Figure 7

PWB warpage by Navier’s Fourier approximation predicting the reverse saddle warpage of the board at the LGA area. All dimensions shown above are in inches.

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Figure 6

Cooper sensor placements onto PWB test board. Circles indicate where the six sensors resided.

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Figure 5

Close-up of Section 1 of PWB showing a reverse “saddle” shape warpage, where the center of the array is bowing outward (convex) and the leading edge is bowing inward (convex). Magnified Z direction by 50×.

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Figure 4

Surface plot of PWB cubic splines as measured with no modules attached (undeflected). Magnified 50× in transverse (out of plane) direction for clarity. Darker framed areas are where LGA attaches.

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Figure 3

Impression of and LGA using Fuji Pressure Sensitive Film and converted to stress marks by densimeter scanner. Stress marks are then interpreted by use of a color map.

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Figure 2

Module∕LGA∕PWB system. LGA pins behave like small springs sandwiched between module and PWB components.

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Figure 1

Electronic module assembly on a PWB. An individual stack-up is composed of module, LGA connector, PWB, and local stiffener plate.

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