Mechanical shock during a drop impact is reported to be the major cause of damage for portable electronics. However, fundamental knowledge in this new field was highly insufficient. This thesis presents our study on the shock response and shock protection of portable electronics....[ Read more ]

Mechanical shock during a drop impact is reported to be the major cause of damage for portable electronics. However, fundamental knowledge in this new field was highly insufficient. This thesis presents our study on the shock response and shock protection of portable electronics.

First, systematic experiments were carried out to investigate the dynamic behaviors of a typical portable device under drop impact. An idealized system which contained an outer case and a PCB (Printed Circuit Board) with an attached packaged chip was adopted as specimen. The actual impact force pulses were measured by employing a Hopkinson bar in a dynamic test rig. Particular attention was paid to the dependence of the dynamic response of the PCB on the impact velocity, the force pulse, as well as the impact orientation. A simplified analytical model is proposed to interpret the experimental results.

Then, based on the understanding gained from the drop tests, experiments were carried out to evaluate the feasibility of using appropriate shock table tests to mimic the drop environment. A series of shock table test methods were developed and tested. It was found that an appropriate shock table test method should allow the sample to rotate freely.

A series of shock tests were conducted to access different fixation methods of the PCB by using foam and/or rubber cushions. Result shows that strong constraint at boundary may alleviate the strain level near the center of the PCB. However, excessive constrain may cause severe high strain near the supporting points.

Fundamental mechanical models are essential for better understanding of the basic characteristic of the shock performance of products. For impact with a given velocity, the analysis of mass-spring models reveals the relationships between the peak force and the impact velocity, contact spring of outer case and natural frequency of component.

A beam model is employed to study the dynamic response of flexible structures. The beam model demonstrates that many components an be idealized as a mass-spring system, if the responding strain field is dominated by its first mode. However, if the shock duration is much shorter than the natural period, about 10 orders of modes should be considered to get a good estimation.

Some conclusions have been drawn at the end of the thesis and future research work is also suggested.