T.X. Yu

Design of shock table tests to mimic real-life drop conditions for portable electronic device

Mechanical shock tests are very important for portable electronic products such as notebook computers and mobile phones because these products are subjected to high risks of impact loading. Impact loading often plays a critical role in the functional performance and mechanical reliability of electronic components and devices. Drop tests are adopted usually to the overall product to assess the structural and functional integrity. Traditional test method is to drop the products from a certain height with a quick release hook or drop tester. The obvious advantage for these methods is that they can directly duplicate the field impact scenarios. However, the test repeatability can not be guarantied in drop tests, because it is difficult to control the orientation of the object at impact and to instrument it. Moreover; by considering the real impact conditions, drop tests are not applicable for the shock reliability tests of individual components. Shock table tests are carried out to overcome the drawbacks described above. A shock impulse with a given shape, magnitude and duration is applied to the shock table and then imparted to the sample product or component fasted to the table. However, the shock table test is a simulation of the real-life drop impact process. To make the shock table tests adequately mimic the real drop impact, it is critical to make correlation between the shock table test parameter and field conditions. The present paper aims to conduct a systematic study, both experimentally and analytically, to evaluate the feasibility of using appropriate shock table tests to mimic the shock environment for components and systems adopted in portable electronics. Firstly, dynamic characteristics of typical portable electronic systems and components under drop impact are studied, and then effective shock table test methods are developed for adequately mimic the real-life impact state. At last, by comparing the typical results from shock table tests and those from drop tests, the correlation of shock table test parameters and drop tests conditions are investigated.

Design of Shock Table Tests to Mimic Real-Life Drop Conditions

A systematic study, both experimentally and analytically, is conducted to evaluate the feasibility of using appropriate shock table tests to mimic the drop impact environment for components and systems adopted in portable electronics. Firstly, experiments are carried out to observe the dynamic characteristics of typical portable electronic systems and components under drop impact. Then a series of shock table tests with different constraint conditions are designed to mimic the real-life impact state. By comparing the typical results from shock table tests and those from drop tests, the correlation of shock table test parameters and drop tests conditions is investigated. The results reveal that the conventional fully constrained shock table test cannot mimic the real-life drop impact conditions, while an appropriate shock table test method should allow the sample to rotate freely. Theoretical analysis is developed to explain the mechanics of the impact scenarios. It is found that due to Hertz contact spring effect and the rotational acceleration during the impact, the acceleration of the centroid sample is significantly different to that of the table. In addition, acceleration estimated by traditional force-divided-by-mass method may underestimate the real acceleration of components inside the products.

Drop impact of a typical portable electronic device

Drop impact reliability is an important concern for the design and use of portable electronic products. When the product is accidentally dropped on the ground, impact forces are transmitted from the product case to the printed circuit board (PCB) and other components within the case. These forces may cause severe functional damage in the form of component failure and/or interconnection breakage. This paper reports our investigation on the dynamic behaviours of a typical portable electronic device under drop impact loading. Firstly, an idealized system which contains an outer case and a PCB attached with a package was adopted as specimen. With an innovative design, the actual impact force pulses were measured by employing a Hopkinson bar in the dynamic test rig. Dynamic strains of the PCB were simultaneously recorded to explore the correlation between the strains and the impact pulse. Particular attention has been paid to the dependence of the shock response of the PCB on the impact velocity, impact force pulse, as well as the impact orientation. Analysis is carried out to explain the experimental results. A deep understanding of the shock response of typical electronic product systems will help to guide the design of rugged and highly impact-resistant devices