Community Research and Development Information Service - CORDIS

Mathematical models for the prediction of stress levels in flip chip assemblies

Both an analytical and a finite element model have been developed to calculate stress levels and deformations of adhesive bonded flip chip assemblies as a result of the bonding process and of environmental exposure.

The analytical model, dedicated for thermal stresses in packages without under-fill, has shown that a high and wide connection is the best solution. Furthermore, due to the very high thermal stresses (> 50 MPa), it is concluded that under-fills are really necessary to obtain a reliable interconnection..

The FE-model includes stress development due to curing shrinkage, thermal shrinkage and an expansion due to moisture uptake. The 3D model has shown to accurately describe the phenomena and trends that are experimentally observed during flip-chip bonding on different substrates. However, the verification work showed that there is still a large deviation of calculated deformation levels from measured data. Potential model improvements have already been identified.

The result largely consists of a 3D finite element model, that besides thermal and mechanical stresses is able to calculate stresses build up during curing and stresses due to moisture uptake and release. As indicated before, the model although predicting the trends in a correct way, needs further adaptation to improve quantitative agreement with measured data.

The model (after this further improvement) can be used for a wide variety of applications using thermosetting polymer systems (adhesive/encapsulate or coating), also outside the primary application fields in microelectronics (besides flip chip, also e.g. optical/mechanical constructions, potting/adhesive bonding in ballasts and lamps for lighting applications).

State of the art calculations on encapsulate/adhesive constructions, even in case of viso-elastic approach, generally do not take into account stresses generated during curing and due to moisture, although these stresses according to the present project can be very significant and dominant. The model used in the present project is based on well known software (MARC), which was, however, extensively modified with subroutines in order to incorporate the extra variables of curing and moisture uptake. Parts of the result are also material properties measured, e.g. shrinkage build-up with either advanced home made interferometric equipment or modified commercially available equipment.

Reported by

Philips Centre for Manufacturing Technology
Eindhoven
Netherlands
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