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Research Papers

Influence of Secondary Impact on Printed Wiring Assemblies—Part II: Competing Failure Modes in Surface Mount Components

[+] Author and Article Information
Jingshi Meng

Mechanical Engineering Department,
Center for Advanced Life Cycle
Engineering (CALCE),
University of Maryland,
College Park, MD 20742
e-mail: mengjshi@umd.edu

Abhijit Dasgupta

Mechanical Engineering Department,
Center for Advanced Life Cycle
Engineering (CALCE),
University of Maryland,
College Park, MD 20742
e-mail: dasgupta@umd.edu

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received September 26, 2015; final manuscript received March 1, 2017; published online June 14, 2017. Assoc. Editor: Jeffrey C. Suhling.

J. Electron. Packag 139(3), 031001 (Jun 14, 2017) (12 pages) Paper No: EP-15-1102; doi: 10.1115/1.4036187 History: Received September 26, 2015; Revised March 01, 2017

Portable electronic devices are commonly exposed to shock and impact loading due to accidental drops. After external impact, internal collisions (termed “secondary impacts” in this study) between vibrating adjacent subassemblies of a product may occur if design guidelines fail to prevent such events. Secondary impacts can result in short acceleration pulses with much higher amplitudes and higher frequencies than those in conventional board-level drop tests. Thus, such pulses are likely to excite the high-frequency resonances of printed wiring boards (PWBs) (including through-thickness “breathing” modes) and also of miniature structures in assembled surface mount technology (SMT) components. Such resonant effects have a strong potential to damage the component, and therefore should be avoided. When the resonant frequency of a miniature structure (e.g., elements of an SMT microelectromechanical system (MEMS) component) in an SMT assembly is close to a natural frequency of the PWB, an amplified response is expected in the miniature structure. Components which are regarded as reliable under conventional qualification test methods may still pose a failure risk when secondary impact is considered. This paper is the second part of a two-part series exploring the effect of secondary impacts in a printed wiring assembly (PWA). The first paper is this series focused on the breathing mode of vibration generated in a PWB under secondary impact, and this paper focuses on analyzing the effect of such breathing modes on typical failure modes with different resonant frequencies in SMT applications. The results demonstrate distinctly different sensitivity of each failure mode to the impacts.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Background: (a) secondary impact FEA model, (b) schematic of test setup, and (c) simplified SMT assembly and its loading conditions

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Fig. 2

Two-step calibration procedure and results, PWB strain

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Fig. 3

High-frequency through-thickness response of laminated PWBs to secondary impacts

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Fig. 4

Two-DOF analytic model with two competing failure modes

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Fig. 5

Parameter extraction for analytic 2DOF model from FEA model of an MEMS component

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Fig. 6

Transfer functions of the 2DOF model

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Fig. 7

Sample outputs from the 2DOF model, 1.2 mm clearance, no trench, ζi = ζa = ζb = 0.05, and fp = 0.5 MHz

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Fig. 8

FEA half-symmetric model for FM-b

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Fig. 9

FEA model for FM-a

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Fig. 10

Sample contour plot for FM-b

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Fig. 11

Impact acceleration histories at the footprints of SMT packages, for various clearances

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Fig. 12

Acceleration from direct (no trench) and indirect (with trench) impacts for 0.6 mm clearance

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Fig. 13

Test conditions in Table 2

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Fig. 14

Amplifications of x1 and x2 for impact pulses with various tp and fp pulses, based on two approximations of γ

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Fig. 15

Sensitivity of FM-a and FM-b to secondary impacts

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Fig. 16

Sensitivity of FM-a and FM-b to direct and indirect impacts

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Fig. 17

Sensitivity of FM-a and FM-b to clearance

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Fig. 18

PWB strain underneath the components

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Fig. 19

Sensitivity of FM-a and FM-b to contact stiffness

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Fig. 20

Schematics of the three test conditions

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Fig. 21

Sample probability density function and failure mode

Tables

Errata

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