Characterization and modeling of static and cyclic relaxation in nonconductive adhesives |
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Authors: | M Gunawan E H Wong S G Mhaisalkar L T Davila Yu Hong J F J M Caers T K Tsai |
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Affiliation: | (1) School of Materials Engineering, Nanyang Technological University, 639798 Singapore;(2) Institute of Microelectronics, 117685 Singapore;(3) Philips Electronics Singapore, 319762 Singapore;(4) Instron Corporation, 118228 Singapore |
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Abstract: | Adhesive interconnections are considered to be attractive alternatives to lead or lead-free solder interconnects because of
their lower processing temperatures and extendability to fine pitch applications. However, reliability issues, such as moisture-induced
delamination and viscoelastic relaxation of the adhesive in both steady-state and cyclic loading, continue to pose a challenge
to widespread implementation. To date, the static and cyclic relaxation characteristics of nonconductive adhesives (NCAs)
are yet to be understood. This paper attempts to provide insights into this static and cyclic relaxation behavior through
experimental characterization and modeling. The viscoelastic property of a typical NCA material was characterized, and a simulation
program with integrated circuit emphasis (SPICE) modeling program was used to model the cyclic relaxation behavior. The modeling
results were successfully validated with a series of experiments. This showed that cyclic relaxation of the adhesive can be
successfully modeled using linear-viscoelastic property. The phenomenon of slower relaxation of the adhesive under cyclic
loading than that in static loading suggests that accelerated reliability testing used in solder-joint fatigue durability
investigations may not be directly applicable to the adhesive interconnections. A rework methodology applicable to adhesive
interconnects using cyclic loading has also been proposed. |
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Keywords: | Mechanical-electrical analogy simulation program with integrated circuit emphasis (SPICE) static and cyclic stress relaxation |
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