Modeling Residual Stresses in Epoxies During Cooling

There are many ways to attach optoelectronic components. Epoxy bonding is attractive due to cost advantages, however, there are challenges associated with this method of attachment. For example, maintaining alignment, when cooling after cure and after long periods of use can be a concern. A small amount of movement of some components can result in significant losses in coupling efficiency of optoelectronic systems. Since epoxies are

viscoelastic in nature, our ability to model their mechanical behavior is not as accurate as for elastic materials. This paper concentrates on a comparison of a thermorheologically simple, linear viscoelastic material model to a thermorheologically complex, nonlinear viscoelastic material model as a means of predicting cooling stresses in epoxies. Mathematically, a Prony Series approach will be used to model the thermorheologically simple, linear viscoelastic behavior and a Stretched Exponential approach will be used to model the thermorheologically complex, linear viscoelastic behavior. The tensile modulus and stress relaxation modulus functions are used to calculate the stress build up in the epoxy during the cool down from elevated temperatures.