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Research Papers

An Investigation Into the Effect of the PCB Motion on the Dynamic Response of MEMS Devices Under Mechanical Shock Loads

[+] Author and Article Information
Fadi Alsaleem, Ronald Miles

Department of Mechanical Engineering, State University of New York at Binghamton, Binghamton, NY 13902

Mohammad I. Younis

Department of Mechanical Engineering, State University of New York at Binghamton, Binghamton, NY 13902myounis@binghamton.edu

J. Electron. Packag 130(3), 031002 (Jul 29, 2008) (10 pages) doi:10.1115/1.2957319 History: Received January 09, 2007; Revised January 14, 2008; Published July 29, 2008

We present an investigation into the effect of the motion of a printed circuit board (PCB) on the response of a microelectromechanical system (MEMS) device to shock loads. A two-degrees-of-freedom model is used to model the motion of the PCB and the microstructure, which can be a beam or a plate. The mechanical shock is represented as a single point force impacting the PCB. The effects of the fundamental natural frequency of the PCB, damping, shock pulse duration, electrostatic force, and their interactions are investigated. It is found that neglecting the PCB effect on the modeling of MEMS under shock loads can lead to erroneous predictions of the microstructure motion. Further, contradictory to what is mentioned in literature that a PCB, as a worst-case scenario, transfers the shock pulse to the microstructure without significantly altering its shape or intensity, we show that a poor design of the PCB or the MEMS package may result in severe amplification of the shock effect. This amplification can cause early pull-in instability for MEMS devices employing electrostatic forces.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of the assembly (packaging) levels of a MEMS device

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Figure 2

A 2DOF model of a microstructure mounted on a PCB

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Figure 3

Schematic of a half-sine pulse used to model actual shock loads

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Figure 4

Time history for the normalized displacement of the diaphragm for a half-sine pulse of T=1.0ms

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Figure 5

The maximum normalized relative amplitude of the diaphragm for different ωP values. The results are shown for a half-sine pulse for the case of no damping.

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Figure 6

A comparison of the microstructure response to impact shock load using ANSYS and the modal analysis solution

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Figure 7

The maximum normalized relative amplitude of the diaphragm for different ωP and ωpulse values

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Figure 8

The maximum normalized amplitude of the PCB response for different ωP values

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Figure 9

Time history for the normalized relative displacement of the diaphragm when ωP=19.2kHz and T=60μs

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Figure 10

The maximum normalized relative amplitude of the diaphragm for different ωP and ωpulse values when ζ=0.05

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Figure 11

The maximum normalized relative amplitude of the diaphragm for different ωP values when ζ=0.05

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Figure 12

The response of the MEMS-PCB assembly to an impact shock load of shock duration T=1ms: (a) response spectrum and (b) transit response for the continuous-lumped model (19)

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Figure 13

The response of the MEMS-PCB assembly to an impact shock load of shock duration T=0.1ms: (a) response spectrum and (b) transit response for the continuous-lumped model (19)

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Figure 14

Time history for the normalized relative response of the diaphragm to a half-sine pulse of T=0.25ms, showing (a) a stable response when ωP=28.8kHz and Vdc=31V, and (b) a pull-in state (unstable response) when ωP=1.92kHz and Vdc=27V

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Figure 15

A plot of the pull-in voltage of the diaphragm against shock load amplitude of a half-sine pulse, accounting for the PCB motion (solid) and neglecting the PCB motion (dashed). The results are shown for the case T=0.25ms and ωP=2.64kHz.

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Figure 16

The transient response of a capacitive MEMS device with and without a PCB when subjected to base shock load generated by a controllable shaker, as monitored through a laser doppler vibrometer (T=5.0ms, and the ratio between the natural frequency of the PCB to the MEMS is 1.24) (34)

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