Stochastic Characterization and Models to Predict Performance Uncertainty in Photonic Packages

[+] Author and Article Information
S. Radhakrishnan, G. Subbarayan

 Purdue University, 585 Purdue Mall, West Lafayette, IN 47907

L. Nguyen, W. Mazotti

 National Semiconductor Corporation, 3707 Tahoe Way, Santa Clara, CA 95052

J. Electron. Packag 129(3), 229-235 (Oct 22, 2006) (7 pages) doi:10.1115/1.2753885 History: Received December 01, 2004; Revised October 22, 2006

There is considerable uncertainty in the prediction of performance of a system, due mainly to idealizations in geometry, material behavior, and loading history. Uncertainties in geometry can be predicted and controlled using tighter tolerances. However, the models currently used to describe material behavior are mostly deterministic. To predict the coupling efficiency of a photonic system to a greater degree of confidence, stochastic analysis procedures are necessary. As part of such an analysis, the behavior of materials must be stochastically characterized. In this paper, we present extensive experimental data on thermally and UV-cured epoxies, typically used in photonic packages to enable stochastic analysis. We perform dynamic mechanical analysis over a wide frequency and temperature range to determine the viscoelastic behavior of the epoxies. We next derive an analytical description of the time-dependent behavior of a vertical cavity surface emitting laser (VCSEL) array bonded to a substrate. We further characterize the variation in the displacement of the VCSEL array due to the stochastic, viscoelastic behavior of the bond epoxy. We carry out Monte Carlo simulation to predict the uncertainty in the coupling efficiency of a generic photonic package. We finally relate the size of the VCSEL laser array to its ability to achieve the required coupling efficiency.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Fiber-optic system used as a demonstration vehicle

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Figure 2

EMI Emcast 501 epoxy sample used in the DMA test

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Figure 3

Standard solid model used to describe EMI Emcast 501 epoxy

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Figure 4

DMA machine used to characterize the epoxies

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Figure 5

2D model of VCSEL, epoxy, and substrate

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Figure 6

Free-body diagram of the VCSEL epoxy substrate showing the stresses resulting from differential thermal expansion

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Figure 7

Data fit curve for EMI Emcast epoxy at 50°C

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Figure 8

Data fit curve for EMI Emcast epoxy at 80°C

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Figure 9

Data fit curve for EMI Emcast epoxy at 110°C

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Figure 10

Data fit curve for EMI Emcast epoxy at 150°C

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Figure 11

Data fit for E1, with respect to temperature

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Figure 12

Data fit for E2, with respect to temperature

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Figure 13

Data fit for η2, with respect to temperature

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Figure 14

Variation of E1 at 80°C

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Figure 15

Variation of E2 at 80°C

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Figure 16

Variation of η2 at 80°C

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Figure 17

Normalized displacement along the VCSEL array

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Figure 18

Coupling efficiency change due to normalized beam shift

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Figure 19

Coupling efficiency along the length of the VCSEL at different temperatures

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Figure 20

Stochastic variation of coupling efficiency




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