STRESS AND STIFFNESS ESTIMATION FOR CIRCUIT CARDS ASSEMBLIES UNDER DYNAMIC LOADS

Abstract

The paper represents mathematical modeling aimed at estimation of dynamic load response for circuit cards in order to eliminate it or reduce dynamic stress in the circuit card assemblies to the acceptable level and to provide their strength and reliability in conditions of the active vibration exposure. The mathematical model has been designed for dynamic strain and stress calculation in circuit cards, which represents cylindrical bending boards as bending the infinite number of beams-strips having rectangular section and considered a separated oscillatory mechanical system. The system is represented by weightless two-supported beam with concentrated mass in its middle point, which applies not uniform load to oscillatory system and performs the relative motion in non-inertial frame of reference. Thus the model estimates the maximal total normal stress and deflection in the dangerous section of the card applied for strength and stiffness assessment. Mathematical modeling strain and stress condition, vibration analysis and finding resonance frequencies are performed by using methods of theoretical mechanics, strength of materials, applied theory of elasticity and theory of oscillations. The strength and stiffness assessment has been recommended to perform by acceptable stress for the entire circuit card assembly, which is defined with respect to experimentally verified ultimate strength of the solder joint with safety factor that provides stress under ultimate elasticity of the solder. This approach has precised acceptable diapason of vibration by amplitude frequency response of maximal total normal stress and deflection estimated for circuit cards subjected to harmonic oscillation with constant amplitude.