Durability of Large Electronic Components Undergoing Multi-Axial Vibratory Excitation

Abstract

Shaker table vibration testing is nothing new for electronic components. Such environmental tests are most often conducted in a sequential uniaxial setup, where the test article is sequentially rotated and excited along three different orthogonal orientations. While sequential axis testing does excite modes in all three directions sequentially, it does not quantify or qualify how modes along different axes interact with one another when excited simultaneously. Traditional linear dynamics does not predict any cross-axis interactions between different spectral modes in vibrating structures, but this has long been suspected to be an oversimplification for many cases. The authors demonstrated this in a previous experiment, in which printed wiring assemblies (PWAs) of the same design were subjected to sequential uniaxial and simultaneous biaxial excitations. Boards undergoing bi-axial excitation suffered fatigue damage accumulation rates much higher than the superposition of damage rates from sequential uniaxial tests. Even as far back as 2010, the military added multi degree of freedom (MDoF) vibration tests to their 810G standard — so MDoF testing is rapidly gaining traction in the accelerated stress testing community. The cost of performing MDoF vibration durability testing can be significant, so an important technical issue turns into identifying when MDoF testing is necessary, and when single degree of freedom (SDoF) testing is sufficient. This study addresses this issue using a combination of mathematical models and FEA simulations. It is intuitively obvious that larger and more massive circuit components are more susceptible to these nonlinear cross-axis interactions, especially as the excitation levels become significant; however our long term goal is to quantify the effects of such parameters on the nonlinear interactions. The focus of the study is a simple beam with a tip mass — representing a circuit component with leads for mounting to the printed wiring board (PWB). The study also considers the effect of the PWB dynamics on the mechanical response of the circuit element, as it undergoes worst case excitation. The effects of several parameters are investigated, including component properties (e.g. mass, and height) as well as bi-axial excitation conditions (eg. frequency, relative phase and amplitude).