Premium
Rheology Study of Wafer Level Underfill
Author(s) -
Sun Yangyang,
Zhang Zhuqing,
Wong Ching Ping
Publication year - 2005
Publication title -
macromolecular materials and engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 96
eISSN - 1439-2054
pISSN - 1438-7492
DOI - 10.1002/mame.200500149
Subject(s) - materials science , epoxy , rheology , curing (chemistry) , isothermal process , composite material , flip chip , soldering , viscosity , wetting , arrhenius equation , viscoelasticity , wafer , thermodynamics , activation energy , adhesive , chemistry , nanotechnology , physics , layer (electronics)
Summary: As a special epoxy resin material used in the electronics packaging, wafer level underfill (WLU) is studied using a chemorheology approach to provide a fundamental understanding of its reaction dependent rheology behaviors. In this work, the relationship between the molecular weight ( $\overline M _{\rm w}$ ) and the viscosity of the epoxy resins at fixed temperatures has been established. Subsequently an Arrhenius‐Erying equation was used to fit the relationship between viscosity and temperature for given molecular weight epoxies. By combining the two relationships, the viscosity could be modeled as a function of temperature and molecular weight. To obtain the viscosity change of the WLU during the reflow process, the molecular weight change of the underfill was calculated from the degree of curing through the kinetics modeling. A semi‐empirical model was developed to predict the viscosity of the underfill as a function of time and temperature during the curing process. Modeled predictions were compared with experimental data under isothermal and ramping temperatures during curing experiments. The model showed good agreement with the experiments in the early stage of curing reaction. The critical viscosity of the underfill for solder wetting was obtained by wetting experiments, which can be used as the criteria to determine the flowability of the wafer level underfill.Data fitting of the viscosity model at isothermal condition.