Controlling Shock and Vibration in Electronic Products

An optimized total design process for electronic products, emphasizing isolation or negation of shock and vibrations, is necessary to give these devices a fighting chance in the real world. By James W. Fraser and Richard S. Gureghian. The success of a new product depends as much on the care taken with the mechanical as with the electronic excellence of the design. Performance considerations include reliability, service life, vibration tolerance, and the capacity to withstand mechanical shock. The more complex a device or the greater its performance capability, the higher its sensitivity to mechanical shock in the handling environment.

Ruggedizing a product, which is an approach to control the effects of vibration, first requires determining where the vibration is sourced, whether it is coming from within or outside the product. The things within the product that move and shake motors and mechanisms may be the source of the vibration, or the product may be situated in an environment where there is vibration. In either case, the vibration must be controlled.

There are two ways to control vibration: hardening the design or isolating the vibration. When hardening the design, the product is made rigid and tough enough so that dynamic forces generated during vibration do not affect it. With this approach, the product may end up overdesigned, heavy, bulky, or unbecoming. In isolating vibration, however, a controlled resiliency is engineered into the system. The resiliency acts as q mechanical filter that reduces the vibration.

With vibration, the concerns are frequency behavior, the ability to filter the vibration, and the strain capability of the isolator. These are usually low-strain environments. The concerns with mechanical shock are the energy output versus energy input characteristics of the design problem such that the isolator or attenuator can accommodate the transient strains necessary to mitigate the incoming acceleration levels. Higher strains are characteristic of mechanical shock.

Mechanical shock can come from either the handling environment or the manufacturing environment. A product may be mishandled, bumped, and banged while being built or delivered before it gets to the customer and before the warranty is activated.

Impact energy is imparted to the structure of the product and may be sufficient to cause either brittle failure or a ductile-type failure. It can be a structural, misalignment, or total failure resulting in malfunction.

Mechanical shock is generally not isolated; in these cases, controlled resiliency is usually used. One method to attenuate shock is to store energy and release it over a broader time base than the input signal. This allows the shock energy to be released over a longer period of time. The result is lower transmitted accelerations and a safer and more tolerant operating environment. The other way of attenuating mechanical shock is to dissipate the energy through controlled resiliency. Instead of storing and releasing the shock energy, it is dissipated into heat. This results in a smaller bundle of energy with which to cope.