This paper presents a collection of test data showing how the choice of package design and material can have a different effect on performance depending on the loading conditions. Board level temperature cycling, drop (JESD22-B111), and cyclic bend (JESD22-B113) tests were performed on 0.4mm ball pitch packages. Factors investigated for this evaluation include mold compound material, mold cap thickness (0.45 vs. 0.7mm), ball pad finish (NiAu vs. Cu OSP), solder ball composition (SAC305, SAC105, SAC125Ni, Sn3.5Ag), solder volume (ball vs. bump), package material (RoHS vs Green), and board material (RoHS vs Green). The data presented in this paper indicates that lower silver content solder balls perform better under drop conditions, while temperature cycling reliability suffers as silver content decreases.In addition, mold compound material and thickness, die size, and solder volume have the opposite effect depending on the loading condition. The Green material for test board also showed lower performance than RoHS compliant board material.
IntroductionThe reliability of an electronic package is ultimately determined by the environment and application in which it is used. Traditionally, only temperature and power cycling were of concern for board level reliability, and CTE mismatch between the package and the board was considered as the primary failure mechanism. However, due to the proliferation of electronic devices across market segments ranging from automotive to small, hand-held devices, electronic packages experience mechanical loading conditions other than just temperature cycling. Handheld products are prone to being dropped and their keys are pressed millions of times during the useful life to send text messages. Similarly electronic assemblies for telecom and automotive applications experience mechanical bending and shock conditions during installation and actual use conditions. This mechanical drop and cyclic bending due to key press have introduced failure modes where flexibility of the package is more important than the CTE mismatch. These additional failure mechanisms have their implications on package design and material selection. The one-size-fits-all model is no longer suitable for package design and material selection and customization is necessary
We report a clear demonstration of thermal hysteresis and elastic anomaly in the elastic constant, C T , of a shape memory alloy Ni 0:507 Ti 0:493 . The observed hysteresis and anomaly closely match the experimental data from the structural phase transition, the resistivity and the thermoelectric power measurements previously reported. The elastic anomaly was explained using a theory based on the band Jahn-Teller mechanism. The theory allows to predict the detailed nature of the structural transitions and also the symmetry of the Fermi levels.
We report a clear demonstration of thermal hysteresis and elastic anomaly in the elastic constant, C T , of a shape memory alloy Ni 0:507 Ti 0:493. The observed hysteresis and anomaly closely match the experimental data from the structural phase transition, the resistivity and the thermoelectric power measurements previously reported. The elastic anomaly was explained using a theory based on the band Jahn-Teller mechanism. The theory allows to predict the detailed nature of the structural transitions and also the symmetry of the Fermi levels.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.