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Launch Dynamics

Assessment of Need for Solder in Modeling Potted Electronics During Gun-Shot

[+] Author and Article Information
L. E. Reinhardt

e-mail: Lyonel.reinhardt@us.army.mil

J. D. Metz

RDAR-MEF-E,
Analysis and Evaluation Technology Division,
U.S. Army Armament Research Development and Engineering Center,
Picatinny Arsenal, NJ 07806

Manuscript received July 31, 2012; final manuscript received November 9, 2012; accepted manuscript posted January 9, 2013; published online April 19, 2013. Assoc. Editor: Bo S. G. Janzon.

J. Appl. Mech 80(3), 031502 (Apr 19, 2013) (7 pages) Paper No: JAM-12-1360; doi: 10.1115/1.4023336 History: Received July 31, 2012; Revised November 09, 2012; Accepted January 09, 2013

Smart projectiles use electronic components such as circuit boards with integrated circuits to control guidance and fusing operations. During gun-launch, the electronics are subjected to 3-dimensional g-forces as high as 15,000 G. The U.S. Army uses finite element analysis to simulate electronics with high-g, dynamic loads. Electronics are difficult to model due to the large variation in size, from large circuit boards, to very small solder joints and solder pads. This means that to accurately model such small features would require very large models that are computationally expensive to analyze; often beyond the capability of resources available. Therefore, small features such as solder joints are often not included in the finite element models to make the models computationally tractable. The question is: what is the effect on model accuracy without these small features in the model? The purpose of this paper is to evaluate the effect that solder joints and solder pads have on the accuracy of the structural analysis of electronic components mounted on circuit boards during gun shot. Finite element models of simplified circuit boards, chips, and potting were created to do the evaluation. Modal analysis and dynamic structural analysis using typical gun loads were done. Both potting at high temperature (soft) and potting at low temperature (stiff) were used in the dynamic analysis. In the modal analysis there was no potting. All of these models were run with and without solder. In all cases, the results differed between the models with solder and those without. In the models with potting, there was a difference in magnitude and stress distribution between the models with and without solder. This indicates that there is a significant reduction in accuracy when solder is not included in the model.

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References

Figures

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Fig. 1

Model cross section

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Fig. 2

Circuit board details

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Fig. 3

Circuit board without solder

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Fig. 4

Circuit board with solder

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Fig. 5

Load location: loads are applied in three directions to the can bottom

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Fig. 6

Load curves in three directions

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Fig. 9

Von Mises stress of chips with and without solder; 233 K

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Fig. 10

Displacement of chips and circuit board; 233 K

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Fig. 11

Displacement of potting; 233 K

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Fig. 12

Von Mises stress, case 3, 333 K, softer potting

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Fig. 13

Von Mises stress of circuit board and chips, 333 K, softer potting

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