Local PWB and Component Bowing of an Assembly Subjected to a Bending Moment

Abstract

An analytical model is developed for determining the bowing of a component mounted on a printed wiring board (PWB) that is subjected to a bending moment. The model assumes a uniform elastic attach, between the component and the board. The elastic attach is assumed to transmit axial forces and restrain cross-sections of the component against rotation. The closed form solution to the beam equations directly determines the bowing of the component and the board. The solution is then used for computing the forces and moments, and hence, stresses in the leads that can occur in static or vibrational loading of a PWB/component assembly. The present analysis applies to electronic components with uniformly distributed leads in an array format, such as some PGA components, or to the class of components with parallel rows of leads such as a DIP or a SOIC. To demonstrate the solution and whether or not the rotational stiffness of the component leads needs to be considered, three different types of packages are analyzed.