EFFECT OF MULTIAXIAL VIBRATION ON FATIGUE DURABILITY OF ELECTRONIC ASSEMBLIES POPULATED WITH SHORT AND LIGHT COMPONENTS

Abstract

Multiaxial vibration can lead to nonlinear cross-axis interactions, which can significantly affect the fatigue durability of electronic printed circuit assemblies. Depending on the frequency and phase relationship between the in-plane and out-of-plane excitations, there can be significant reduction or increase in fatigue durability. Previous studies used experiments and nonlinear dynamic finite element simulations to highlight this nonlinear impact in tall, heavy electronic components such as insertion-mount inductors, wherein the most severe multiaxial interactions resulted in damage that was twice the linear summation of damage caused by corresponding levels of sequential uniaxial vibrations. The root-cause of the multiaxial effects was determined to be kinematic nonlinear interactions between large deformations in orthogonal axes. This dissertation builds on this work by conducting two related studies described below.The first study in this dissertation builds on a prior parametric study, to confirm the findings stated above for tall, heavy components. Simple beam specimens are designed to represent the kinematic features of tall heavy components with flexible leads mounted on flexible printed circuit boards (PCBs). Single and double beam tests were conducted with varying height and mass to parametrically examine the influence of geometry on nonlinear behavior. The purpose of the single beam configuration is to identify the nonlinear role of the flexible leads and the purpose of the double-beam is to investigate the nonlinear interactions between the flexible leads and the flexible PCBs. The tip response is recorded for various uniaxial and multiaxial excitation profiles to establish the nonlinear interactions. Dynamic, nonlinear finite element analysis (FEA) is also performed, to validate the experimental results, confirming that kinematic nonlinearity plays a crucial role in the observed multiaxial nonlinear effects. The second part of this study extends the multiaxial vibration durability investigation to examine the feasibility of nonlinear multiaxial interactions in short, light components, such as surface-mount gull-wing quad-flat packages (QFPs), since the deformation magnitudes (and hence the kinematic nonlinear interactions) are expected to be significantly smaller in such cases. Two different types of QFP components are used in printed circuit assemblies (PCAs): QFP100 and a low-profile component LQFP100. Multiaxial random vibration experiments conducted in this study demonstrate that even these light, low-profile components exhibit strong multiaxial nonlinear effects. In fact, the lower-profile LQFP100 demonstrates even higher multiaxial interaction than the regular profile QFP100. These unexpected findings suggest the presence of an additional source of nonlinearity for cross-axis interaction: possibly cross-axis interaction due to material nonlinearity. The failure mode is revealed to be predominantly lead fatigue in both QFP100 and LQFP100 assemblies. To further explore these nonlinear effects, multi-scale nonlinear dynamic finite element models of QFP100 and LQFP100 assemblies are developed and vibration response is simulated for both uniaxial and multiaxial vibration. In the interest of model simplification, the finite element simulations are limited to harmonic analysis, since the underlying physics of the nonlinearity is expected to be the same for both random and harmonic vibration. These models are used to analyze strain distributions in the leads and to conduct fatigue analysis, providing deeper insights into the material and geometric interactions that lead to multiaxial nonlinear effects. The simulations confirm the trends of the experimental results, illustrating that multiaxial vibration can generate complex nonlinear interactions even in short, light electronic components under multiaxial vibration. This dissertation highlights the importance of considering multiaxial nonlinear effects when designing and qualifying electronic components for dynamic environments, regardless of height or mass. The findings emphasize the need for comprehensive testing and modeling approaches to accurately assess the reliability and durability of electronic assemblies that are subjected to multiaxial vibrations, for both heavy, tall components as well as light, short components.