Influence of Secondary Impact on Failure Modes in PWAs With High Resonant Frequency

2015 ◽  
Author(s):  
Jingshi Meng ◽  
Abhijit Dasgupta
Keyword(s):  
Stress Wave ◽  
Failure Modes ◽  
Short Pulse ◽  
Stress Wave Propagation ◽  
Printed Wiring Boards ◽  
Resonant Frequencies ◽  
Secondary Impact ◽  
Internal Structures ◽  
Printed Wiring Assemblies ◽  
High Frequency Content

Thinner printed wiring assemblies (PWA) and smaller clearances are driven by the continuing increase of functionality and miniaturization in portable electronic devices. The probability of secondary impact during accidental drop and impact between a circuit card and adjacent components increases with the decrease in the size and weight of the product. In particular, compared to the initial impact, impulses caused by contact during secondary impacts are typically characterized by significant increase of amplitudes and extremely short pulse widths. As a result, stress wave transmission and reflection in printed wiring boards (PWBs) can be at a frequency range close to the resonant frequencies of PWA components with miniature internal structures, such as MEMS. This study focuses on analyzing the high frequency content of the accelerations due to stress wave propagation, reflections and dispersions in the thickness direction of multilayered PWBs, caused by secondary impact, and on the consequential effects on typical failure modes with high resonant frequencies.

Influence of Secondary Impact on Printed Wiring Assemblies—Part I: High-Frequency “Breathing Mode” Deformations in the Printed Wiring Board

2016 ◽  
Vol 138 (1) ◽  
Author(s):  
Jingshi Meng ◽  
Abhijit Dasgupta
Keyword(s):  
Microelectromechanical Systems ◽  
Electronic Device ◽  
Frequency Bandwidth ◽  
Printed Wiring Board ◽  
Resonant Frequencies ◽  
Breathing Mode ◽  
Secondary Impact ◽  
Internal Structures ◽  
Wiring Board ◽  
Printed Wiring Assemblies

Design rules for portable electronic device are continuously striving for thinner printed wiring assemblies (PWAs) and smaller clearances because of ever-increasing demand for functionality and miniaturization. As a result, during accidental drop and impact events, there is an increased probability of internal secondary impact between a PWA and adjacent internal structures. In particular, compared to the initial impact, acceleration pulses caused by contact during secondary impacts are typically characterized by significant increase of amplitudes and frequency bandwidth. The resonant response in the thickness direction of printed wiring boards (PWBs) (termed the dynamic “breathing mode” of response, in this study) acts as a mechanical bandpass filter and places miniature internal structures in some components (such as microelectromechanical systems (MEMS)) at risk of failure, if any of them have resonant frequencies within the transmitted frequency bandwidth. This study is the first part of a two-part series, presenting qualitative parametric insights into the effect of secondary impacts in a PWA. This first part focuses on analyzing the frequency spectrum of: (i) the impulse caused by secondary impact, (ii) the energy transmitted by the dynamic “breathing” response of multilayer PWBs, and (iii) the consequential dynamic response of typical structures with high resonant frequencies that are mounted on the PWB. Examples include internal deformable structures in typical surface mount technology (SMT) components and in MEMS components. The second part of this series will further explore the effects of the breathing mode of vibration on failures of various SMT components of different frequencies.

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

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Jingshi Meng ◽  
Abhijit Dasgupta
Keyword(s):  
Failure Modes ◽  
Test Methods ◽  
Design Guidelines ◽  
Printed Wiring Boards ◽  
Secondary Impact ◽  
Surface Mount ◽  
External Impact ◽  
Drop Tests ◽  
Board Level ◽  
Printed Wiring Assemblies

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.

scholarly journals Mechanical Properties and Failure Modes of CRCB Specimen Under Impact Loading

2022 ◽  
Author(s):  
Wenjie Liu ◽  
Ke Yang ◽  
Litong Dou ◽  
Zhen Wei ◽  
Xiaolou Chi ◽  
...  
Keyword(s):  
Impact Velocity ◽  
Stress Wave ◽  
Failure Modes ◽  
Rock Strength ◽  
Peak Strength ◽  
Stress Wave Propagation ◽  
Peak Strain ◽  
Impact Tests ◽  
Coal Particles ◽  
The Impact

Abstract To explore the dynamic mechanical characteristics of coal-rock combined body (CRCB) load-bearing structures, impact tests were performed on CRCB specimens by using a separated Hopkinson pressure bar test device (SHPB) combined with an ultra-high-speed camera system. The propagation characteristics of stress wave , dynamic stress-strain relationship, energy evolution law, and distribution characteristics of CRCB crushed particles in the impact tests were analyzed. The obtained results showed that: with the increasing of impact velocity, the effect of the wave impedance difference between the CRCB specimens and incident bar on stress wave propagation is gradually weakened. The peak strength (sII) and peak strain of the CRCB had obvious strain-rate effects, the ratio of reflected energy decreases linearly. In addition, with increased impact velocity, the growth rate of the peak strength and ratio of absorbed energy gradually dropped, changing approximately as a power function. Macro-fractures of the CRCB mainly occurred at the coal or rock ends which is far away from the interface. When the stress at the crack tip is greater than the "weakened" coal or rock strength, the crack will continue to develop across the coal and rock interface. With the increasing of impact velocity and rock strength, the crushed coal particles gradually transform from massive to powdering, and the average size of crushed coal blocks decreases, which leads to a gradual increase in the fractal dimension of the CRCB specimens. Therefore, the monitoring and prevention of dynamic loads should be strengthened in the coal mines with thick and hard roofs.

FEM Stress Analysis and Strength of Scarf Adhesive Joints of Similar Adherend Subjected to Impact Tensile Loadings

2007 ◽  
Author(s):  
Toshiyuki Sawa ◽  
Yuya Hirayama ◽  
He Dan
Keyword(s):  
Young’S Modulus ◽  
Principal Stress ◽  
Stress Wave ◽  
Young's Modulus ◽  
Three Dimensional ◽  
Maximum Principal Stress ◽  
Adhesive Joints ◽  
Stress Wave Propagation ◽  
Adhesive Thickness ◽  
Three Dimensional Finite Element

The stress wave propagation and stress distribution in scarf adhesive joints have been analyzed using three-dimensional finite element method (FEM). The FEM code employed was LS-DYNA. An impact tensile loading was applied to the joint by dropping a weight. The effect of the scarf angle, Young’s modulus of the adhesive and adhesive thickness on the stress wave propagations and stress distributions at the interfaces have been examined. As the results, it was found that the point where the maximum principal stress becomes maximum changes between 52 degree and 60 degree under impact tensile loadings. The maximum value of the maximum principal stress increases as scarf angle decreases, Young’s modulus of the adhesive increases and adhesive thickness increases. In addition, Experiments to measure the strains and joint strengths were compared with the calculated results. The calculated results were in fairly good agreements with the experimental results.

Effect of interlayer on stress wave propagation in CMC/RHA multi-layered structure

2010 ◽  
Vol 70 (12) ◽  
pp. 1669-1673 ◽  
Author(s):  
Yangwei Wang ◽  
Fuchi Wang ◽  
Xiaodong Yu ◽  
Zhuang Ma ◽  
Jubin Gao ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Stress Wave ◽  
Layered Structure ◽  
Stress Wave Propagation
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