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RESEARCH PAPERS

Solder Joint Shape Prediction Using a Modified Perzyna Viscoplastic Model

[+] Author and Article Information
Mudasir Ahmad

 Interconnect Technology Team, Manufacturing Technology Group, Cisco Systems, Inc., 170 W Tasman Drive, San Jose, CA 95134mudasir.ahmad@cisco.com

Ken Hubbard, Mason Hu

 Interconnect Technology Team, Manufacturing Technology Group, Cisco Systems, Inc., 170 W Tasman Drive, San Jose, CA 95134

J. Electron. Packag 127(3), 290-298 (Oct 05, 2004) (9 pages) doi:10.1115/1.1938985 History: Received April 18, 2004; Revised October 05, 2004

Ball grid array solder joint reliability is known to be dependent on the shape of solder joints after reflow. To ensure good solder joint formation and prevent solder bridging, it is critical to understand the amount of paste volume needed during assembly and reflow. The final shape of the solder joint is a function of surface tension, wetting area, gravity, and applied forces. In this paper, a new methodology to simulate solder joint shape is presented. Large deformation viscoplastic finite element analysis is used to simulate incompressible fluid flow. A numerical model for surface tension is outlined and validated with closed-form solutions. The results of the numerical model are compared to other known solder joint shape prediction methods. The effects of package weight, coplanarity, warpage, paste volume, pad misregistration, and joint construction on solder joint shape are then analyzed. Recommendations are provided on ways to maximize standoff height and avoid bridging. Finally, the formation of leadless solder joints is studied and compared to experimental data.

Copyright © 2005 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Surface-tension force balance

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Figure 2

The ANSYS SURF 154 Surface Effect Element

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Figure 3

Solid 185 overlaid with Surf 154

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Figure 4

Pressure distribution

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Figure 5

Hydrostatic pressure to include gravity

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Figure 7

Comparison of Kitano’s deformed shape (left) and the Perzyna deformed shape (right). Wire frame shows undeformed shape, and solid contour shows final deformed shape under 8×10−4N.

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Figure 8

(a) Comparison of Goldmann’s results and the Perzyna deformed shape (b) Comparison of Goldmann’s results and the Perzyna deformed shape

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Figure 9

Solder mask defined versus non-solder-mask-defined solder joints

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Figure 10

Warpage versus max diameter for bridging solder joint

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Figure 11

Bridging of solder joints: wireframe (unwarped), contour (warped)

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Figure 12

Leadless package: solder joint schematic

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Figure 13

Amkor Micro lead frame™ package schematic

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Figure 14

MLF™ package: undeformed and deformed shape

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Figure 15

MLF Package: Experimental data

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