Explicit Submodeling and Digital Image Correlation Based Life-Prediction of Leadfree Electronics under Shock-Impact Pradeep Lall, Sandeep Shantaram, Arjun Angral, Mandar Kulkarni Auburn University Department of Mechanical Engineering NSF Center for Advanced Vehicle and Extreme Environment Electronics (CAVE 3 ) Auburn, AL 36849 Tele: (334) 844-3424 E-mail: lall@eng.auburn.edu Abstract Relative damage-index based on the leadfree interconnect transient strain history from digital image correlation, explicit finite-elements, cohesive-zone elements, and component’s survivability envelope has been developed for life-prediction of two-leadfree electronic alloy systems. Life prediction of pristine and thermally-aged assemblies, have been investigated. Solder alloy system studied include Sn1Ag0.5Cu, and 96.5Sn3.5Ag. Transient strains during the shock-impact have been measured using digital image correlation in conjunction with high-speed cameras operating at 50,000 fps. Both the board strains and the package strains have been measured in a variety of drop orientations including JEDEC horizontal drop orientation, vertical drop orientation and intermediate drop orientations. In addition the effect of sequential stresses of thermal aging and shock- impact on the failure mechanisms has also been studied. The thermal aging condition used for the study includes 125°C for 100hrs. The presented methodology addresses the need for life prediction of new lead-free alloy-systems under shock and vibration, which is largely beyond the state of art. Three failure modes have been predicted including interfacial failure at the copper-solder interface, solder-PCB interface, and the solder joint failure. Explicit non-linear finite element models with cohesive-zone elements have been developed and correlated with experimental results. Velocity data from digital image correlation has been used to drive the attachment degrees of freedom of the submodel and extract transient interconnect strain histories. Explicit finite-element sub-modeling has been correlated with the full-field strain in various locations, orientations, on both the package and the board-side. The survivability of the leadfree interconnections under sequential loading (thermal aging and shock-impact) from simulation has been compared with pristine circuit assemblies subjected to shock-impact. Sequential loading changes the failure modes and decreases the drop reliability as compared to the room temperature experimental results. Damage index based survivability envelope is intended for component integration to ensure reliability in harsh environments. Introduction Electronics may be subjected to shock, vibration, and drop- impact during shipping, handling and during normal usage. Failure-modes include solder-joint failures, pad cratering, chip-cracking, copper trace fracture, and underfill fillet failures. Previously, prediction of transient dynamics has been investigated using equivalent layer models [Gu 2005], smeared property models [Lall 2004, 2005], Conventional shell with Timoshenko-beam Element Model and the Continuum Shell with Timoshenko-Beam Element Model [Lall 2006 a,b , 2007 a-e , 2008 a-d ], implicit global models [Irving 2004, Pitaressi 2004], and global-local sub-models [Tee 2003, Wong 2003, Zhu 2001, 2003, 2004]. However, in product application transient dynamic stresses may be imposed on parts with accrued thermo-mechanical damage. Life prediction in presence of sequential and simultaneous transient-dynamic and thermal loads is presently beyond the state of art. Insight into the nature of damage initiation and progression will enable the formulation of damage relationships for life-prediction in shock environments. Material deformation under high strain rates, previously, has been incorporated in simulation frameworks using linear- elastic models and elastic-plastic models [Lall 2004, 2005, 2006 a-c , 2007 a-e , 2008 a-d , Xie 2002, 2003, Wu 1998, 2000] for interconnects. In this study, the leadfree alloys studied include Sn1Ag0.5Cu and Sn3.5Ag solders. Previous researchers have studied the variation of solder alloy composition on reliability including the effect of low silver content on leadfree drop reliability [Zhu 2008, Che 2008, Lall 2008 a, c, d , Pandher 2008, 2007, Kim 2007], effect of creep rate by lowering silver content of SAC alloys [Zhang 2008], effect of Ni on drop reliability of SnAgCu alloys [Song 2008, Huang 2007, Kawashiro 2008]. Previously, Digital Image Correlation (DIC) has been used in the electronic industry for various applications. DIC has been used to measure full field displacement and deformation gradient in electronic assemblies subjected to drop and shock [Lall 2007 b , 2008 a,b , Miller 2007, Park 2007 a,b , 2008], damping ratio on the surface of the board [Peterson 2008] examination of velocity, rotation, bending on portable products subjected to impact test [Scheijgrond 2005], stresses in solder interconnects of BGA packages under thermal loading [Bieler 2006, Rajendra 2002, Sun 2006, Xu 2006, Yogel 2001, Zhang 2005, Zhou 2001], stresses and strain in flip-chip die under thermal loading [Kehoe 2006]. The use of digital image correlation for development of fatigue constants for solder interconnects subjected to shock and vibration is new. In this paper, explicit sub-modeling in conjunction with DIC based life prediction of solder interconnects has been developed for two different lead-free solder alloys in drop and shock environment. In this work, attempt is made to 978-1-4244-4476-2/09/$25.00 ©2009 IEEE 542 2009 Electronic Components and Technology Conference