Explicit FE-Models and High Speed DIC for Transient-Dynamics of Electronics Pradeep Lall 2 , Dhananjay Panchagade 2 , Deepti Iyengar 2 , Sandeep Shantaram 2 , Jeff Suhling 2 , Hubert Schrier 1 2 Auburn University Department of Mechanical Engineering and Center for Advanced Vehicle Electronics, Auburn, AL 36849 1 Correlated Solutions, West Columbia, SC 29171 Tele: (334) 844-3424 E-mail: lall@eng.auburn.edu ABSTRACT Electronics may be subjected to shock, vibration, and drop-impact during shipping, handling and during normal usage. Measurement of transient dynamic deformation of the electronics assemblies during the shock and vibration can yield significant insights in understanding the occurrence of failure modes and the development of failure envelopes. Failure-modes include solder-joint failures, pad cratering, chip-cracking, copper trace fracture, and underfill fillet failures. Previous researchers have measured the transient-dynamics of board assemblies with high-speed imaging in conjunction with high- speed image analysis for measurement of relative displacement, angle, velocity, and acceleration [Lall 2006, Che 2006]. In addition, high-speed data-acquisition systems with discrete strain gages have been used for measurements of transient strain [Lall 2004, 2005, Liang 2005] and with accelerometers for measurement of transient acceleration [Dunford 2004, Goyal 2000, Seah 2005]. Development of accurate models requires better understanding of full-field strain deformation in board assemblies. In this paper, the use of digital image correlation (DIC) with ultra high-speed imaging has been used for full-field measurement of transient strain in various board assemblies subjected to shock in various orientations. Measurements have been taken on both the package and the board side of the assemblies. Accuracy of high-speed optical measurement has been compared with that from discrete strain gages. Package architectures examined include-flex ball-grid arrays, tape-array ball-grid arrays, and metal lead-frame packages. Explicit finite-element models have been developed and correlated with experimental data. Models developed include, smeared property models, Timoshenko-beam models, and explicit sub-models. The solder strains have been computed from the explicit finite element models for life prediction in shock. INTRODUCTION High speed photography has been used to measure deformation and strain in sheet metal forming analysis, automotive crash testing, rail vehicle safety [Kirpatrick 2001], air-plane safety [Marzougui 1999], modal analysis of blades, disks, shearography which involves laser NDT for rapid honeycomb delamination tests, dynamic fracture phenomenon, tire tests, rotating components, exhaust manifolds, split Hopkinson bar tests, package integrity or hermiticity (MIL-STD-883) tests. High-speed cameras measure impact speed, force, and deformation due to shock, and thermal loading. It is also used for quantitative evaluation of in-plane deformation characteristics of geo-materials [Watanabe 2005], and in medical fields to assess local failure of bone by implementing mechanical compression testing of bone samples [Thurner 2005]. Previously, the measurement of derivatives of field quantities, such as strains, was limited to a specific physical locations or discrete target points in an electronic structure. It was not feasible to extract data at a very large number of locations by using discrete targets because of the time-consuming process. Techniques such as Moiré Interferometry is an option to get the overall deformation contour, but it is often time consuming and involves expensive grates. Digital Image Correlation (DIC) is the state-of-art technique which super-cedes the later as it is less time consuming. The sample preparation is simple and quick. The test specimens are speckle painted and transient deformation recorded with the help of high-speed cameras, to enable the measurement of full-field strains. Feasibility of this technique has been explored in this paper and has been experimented on electronic assemblies under free drop and constrained drop for the first time.