Health monitoring for damage initiation & progression during mechanical shock in electronic assemblies

Electronic products may be subjected shock and vibration during shipping, normal usage and accidental drop. High-strain rate transient bending produced by such loads may result in failure of fine-pitch electronics. Current experimental techniques rely on electrical resistance for determination of failure. Significant advantage can be gained by prior knowledge of impending failure for applications where the consequences of system failure may be catastrophic. This research effort focuses on an alternate approach to damage-quantification in electronic assemblies subjected to shock and vibration, without testing for electrical continuity. The proposed approach can be extended to monitor product-level damage. In this paper, statistical pattern recognition and leading indicators of shock-damage have been used to study the damage initiation and progression in shock and drop of electronic assemblies. Statistical pattern recognition is currently being employed in a variety of engineering and scientific disciplines such as biology, psychology, medicine, marketing, artificial intelligence, computer vision and remote sensing based in Jain, et. al. (2000). The application quantification of shock damage in electronic assemblies is new. Previously, free vibration of rectangular plates has been studied by various researchers as presented in Leissa (1969), Young (1950), Gorman (1982), Gurgoze (1984), and Wu (2003) for development of analytical closed-form models. In this paper, closed-form models have been developed for the eigen-frequencies and mode-shapes of electronic assemblies with various boundary conditions and component placement configurations. Model predictions have been validated with experimental data from modal analysis. Pristine configurations have been perturbed to quantify the degradation in confidence values with progression of damage. Sensitivity of leading indicators of shock-damage to subtle changes in boundary conditions, effective flexural rigidity, and transient strain response has been quantified. A damage index for experimental damage monitoring has been developed using the failure indicators. The above damage monitoring approach is not based on electrical continuity and hence can be applied to any electronic assembly structure irrespective of the interconnections. The damage index developed provides parametric damage progression data, thus removing the limitation of current failure testing, where the damage progression can not be monitored. Hence the proposed method does not require the assumption that the failure occurs abruptly after some number of drops and can be extended to product level drops.