Mechanical Modeling and Characterization of the Curing Process of Underfill Materials

Abstract

Thermo-setting polymers are widely used as underfill materials to improve the reliability of electronic packages. In the design phase, the influence of underfill applications on reliability is often judged through thermal and mechanical simulations, under assumed operating conditions. Because of lacking insight into the mechanical processes due to polymer curing, the impact of processing induced residual stress fields is often neglected. To investigate the evolution of stress and strain fields during the curing process it is important to assume a more appropriate starting point for subsequent process modeling. Furthermore, study of possible damage originating from the fabrication process then comes within reach. To facilitate future analysis of stress and strain fields during the curing process a cure dependent constitutive relation is assumed. An approximate investigation method for the process-dependent mechanical properties, based on Dynamic Mechanic Analysis (DMA), is developed. As an illustration the parameter identification is performed for a selected epoxy resin.

A small-strain model to simulate the curing of thermosets

“…In processes that glue electronic components to plates, shrinkage-and/or temperature-induced stresses can lead to damage or even to failure of either the adhesive layer or the whole component [2,5]. Recent research has demonstrated that a careful selection of processing parameters dramatically reduces warpage which suggests that process modelling can be a powerful tool for determining optimal curing conditions [6].…”

Characterization of the viscoelastic properties of an epoxy molding compound during cure

“…Furthermore, they [5] extracted a full cure dependent viscoelastic model for the shear modulus of a commercial molding compound by monitoring the changes in the viscoelastic properties of the compounds during cure. A cure-dependent viscoelastic model was also proposed [6][7][8][9] to describe the evolution of the viscoelastic behavior of an underfill resin in a flip chip package during isothermal and non-isothermal cure.…”

Investigation on flip chip solder joint fatigue with cure-dependent underfill properties

“…More detailed description about the model and the experimental methodology can be found in [8]- [10].…”

“…The temperature dependent Young's modulus is given by [13] (9) where is the temperature in . The yield behavior is described by the following equation [14]: (10) where is the absolute temperature . The creep behavior is described as [13] (11) where equivalent creep strain rate; equivalent stress; Young's modulus; activation energy; universal gas constant; absolute temperature; material constant.…”

“…Ernst et al [8] generalized the method. Further it was applied for describing cure-dependent viscoelastic behavior of epoxy resin [9], [10] and was used to investigate the effect of curing process induced stresses on the die cracking stress of a Flip Chip [11].…”