Computational Methods and High Speed Imaging Methodologies for Transient-Shock Reliability of Electronics

Abstract

Product level assessment of drop and shock reliability relies heavily on experimental test methods. Prediction of drop and shock survivability is largely beyond the state- of-art. However, the use of experimental approach to test out every possible design variation, and identify the one that gives the maximum design margin is often not feasible because of product development cycle time and cost constraints. In this paper, the modeling approaches and high-speed experimental techniques for first-level solder interconnects in shock and drop of electronics assemblies have been discussed. The shock and vibration reliability prediction of electronic interconnects involves multiple scales from macro-scale transient-dynamics of electronic assembly to micro-structural damage history of interconnects. Previous modeling approaches include, solid-to-solid sub-modeling using a half test PCB board, shell-to-solid sub-modeling technique using a quarter- symmetry model. Inclusion of model symmetry in state- of-art models saves computational time, but targets primarily symmetric mode shapes. Explicit modeling approaches has been presented, which enable prediction of both symmetric and anti-symmetric modes, which may dominate an actual drop-event. Approaches presented include, smeared property models, Timoshenko-beam element models, explicit sub-models, and continuum-shell models. A failure-envelope approach based on wavelet transforms and damage proxies has been discussed to model drop and shock survivability of electronic packaging. Data on damage progression under transient- shock and vibration in both 95.5 Sn 4.0 Ag 0.5 Cu and 63 Sn 37 Pb ball-grid arrays has been presented. The concept of relative damage index has been used to both evaluate and predict damage progression during transient shock. The failure-envelope provides a fundamental basis for development of component integration guidelines to ensure survivability in shock and vibration environments at a user-specified confidence level. Transient dynamic behavior of the board assemblies in free and JEDEC-drop has been measured using highspeed strain and displacement measurements. Correlation of model predictions with dynamic measurements has been presented for acceleration, strain and resistance using high-speed data acquisition systems capable of capturing in-situ strain, continuity and acceleration data in excess of 5 million samples per second. Ultra high-speed video at 150,000 fps per second has been used to capture the deformation kinematics. Life Prediction have been correlated with experimental data for both leaded and leadfree ball-grid arrays.