Time, temperature, and mechanical fatigue dependence on underfill adhesion

The observations of the present study show that underfill properties can vary greatly after the initial cure and that these changes can have a significant effect on adhesion. Temperature studies illustrate that underfill adhesion is a strong function of temperature near its glass transition temperature and reveal the importance of adhesion tests at the temperature extremes of the operating conditions and/or reliability thermal cycling tests. Subcritical crack growth results demonstrate that subcritical strain energy release rates do not necessarily scale with critical strain energy release rates. These results are used to create a new adhesion screening methodology that more closely mimics the time, temperature, and mechanical fatigue conditions that an underfilled 1^st level package will typically experience.