Systematic improvement of support locations for vibrating circuit cards

It is recognized that the mechanical response of a circuit card, subject to dynamic disturbances, can lead to system degradation and perhaps ultimately, the complete loss of functionality of the package. It is clear that in order to increases the reliability of these packages it is necessary to diminish the effects of these dynamic loads. One way to achieve this is to shift the natural frequency of the circuit card away from any resonant forcing frequencies, typically by increasing the fundamental frequency of the card, so that its dynamic displacements are successively reduced. This is often achieved by introducing point supports under the card to stiffen it, thereby increasing the card's fundamental frequency. To this end, it is desirable to understand the relationship between the point support locations and the resulting fundamental frequency of the circuit card so that the supports can be efficiently placed so as to achieve the highest fundamental frequency. This paper approaches this problem by developing techniques for the vibration modeling of printed circuit cards and appropriate methodologies for the selection of support locations. The finite element method and structural dynamic modification techniques are combined with a sequential search algorithm to systematically improve the location of point supports for a circuit card populated with components. It is found that the proposed methodology can be useful for efficiently determining the support locations of a circuit card so as to increase it's fundamental natural frequency.