Polymeric die-attach adhesives have been widely utilized for attaching the sensor die to the lead-frame substrate in the packaging of micro-electro-mechanical systems (MEMS). Although much study has been performed regarding viscoelastic behaviors of packaging materials, less literature has addressed the issue of post-cure shrinkage, which occurs in isothermal storage and in accelerated tests. However, the influence of post-cure shrinkage cannot be ignored in characterizing long-term viscoelastic properties or evaluating long-term reliability for highly sensitive automotive sensors. In this study, a non-contact digital image correlation (DIC) method was used to characterize the post-cure aging shrinkage on a commercial epoxy-based die attach adhesive. The shrinkage strain of bulk specimens was monitored over a period of isothermal aging. Analysis indicates that the process of post-cure shrinkage can be expressed in terms of exponential time functions. Using hygroscopic shrinking as an analogous process, this aging was introduced into a time-dependent finite element (FE) simulation in ANSYS~®15.0. FE case studies combining both stress and dimensional relaxation indicate that certain differences can occur in the long-term finite element analysis if the shrinkage strain is ignored.
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