Field reliability extrapolations from accelerated tests necessitate simulation of a variety of material behaviors under general loading conditions. The Hierarchical Incremental Single Surface (HiSS) yield function (Desai, C. S., 2001, Mechanics of Materials and Interfaces: The Disturbed State Concept, CRC Press, Boca Raton, FL.) has been applied extensively to a wide range of materials, from solders and silicon to ceramics and geotechnical materials, for simulating continuous-yield elastoplastic and elastoviscoplastic behavior. This work presents a continuous-yield function that avoids problems with HiSS for thermal and tensile loading. Validations are presented for eutectic data of Wang (Wang, Z., Desai, C.S., and Kundu, T., 2001, “Disturbed State Constitutive Modeling and Testing of Joining Materials in Electronic Packaging,” report to NSF for Materials Processing and Manufacturing Division Grant 9812686, University of Arizona, Tucson, AZ). Limitations on the range of validity of the elastoplastic and the Perzyna elastoviscoplastic formulations are discussed.