This thesis comprises a thorough study of the microelectronics packaging process by means of various experimental and numerical methods to estimate the process induced residual stresses. The main objective of the packaging is to encapsulate the die, interconnections and the other exposed internal components by providing mechanical protection, heat dissipation, electrical insulation and etc. It is a three stage process comprising encapsulation of the die, complete polymerization at a preset mold temperature and cooling to room temperature. Thermosetting polymers are used as the encapsulant in this process due to their unique mechanical, thermal and electrical properties. The packaging results in residual stress build-up both during the molding and later due to the cyclic thermo-mechanical loading of the electronic or electromechanical devices in which the encapsulated package is fixed. These residual stresses are initiated by the crosslinking (curing) of the epoxy polymer during the molding. Crosslink formation is the property of the thermosetting polymers, which is accompanied by stiffness build-up and shrinkage under constrained boundary conditions. Besides, the encapsulation molding is conducted at a high cure temperature (≈175oC). Hence, the subsequent cooling to room temperature leads to further shrinkage of the cured polymer along with the other encapsulated package components and the CTE mismatch between the layers adds up to the total residual stress inside the package. The key to a reliable simulation lies in an accurate representation of the material and mechanical behavior of the polymer. In this thesis, the time, temperature and conversion dependent behavior of the epoxy molding compound (EMC) is determined by various experimental methods including DSC, DMA, rheometer and PVT and the relevant material behaviors are modeled and implemented in 1D and 2D numerical methods. For verification of the numerical results a novel experimental method is used providing the real time stress measuring capability during packaging.@en

This paper comprises the numerical approach and the experimental validation technique developed to obtain the residual stresses building up during encapsulation process of integrated circuits. Residual stresses can be divided
into cure and cooling induced parts. The curing originated stress had beenmostly neglected in the literature and a special attention had always been given to detection of the thermal induced stress. In this study, both of the residual
stresses, evolving during packaging, were investigated independently. The material behavior of the epoxy molding compound, EMC, was determined by the series of characterization experiments. The volumetric behavior of the EMC was investigated using PVT analysis, in which the total cure shrinkage of an initially uncured sample and the coefficient of thermal expansion of the same sample after full conversion were determined. The cure kinetics was studied using differential scanning calorimetry, DSC. The dynamic mechanical behavior
was examined by dynamic mechanical analysis,DMA, at a fixed frequency. Besides, the time dependent behavior of the EMC was also determined by implementing the time–temperature superposition, TTS, test set-up inDMA.
The shift factor was modeled using the combination of the WLF equation and the polynomial of second degree. The constitutive equationswere developed based on the applied boundary conditions and the epoxy compound's
mechanical behavior in the respective stage. A two dimensional numerical model was constructed using a commercially available finite element software package. For the experimental verification of the numerically obtained residual stresses a flexible board with the stress measuring chip was encapsulated. The real-time stress data were measured during the encapsulation. Using this technique, the in-plane stresses and the temperature changes during the die encapsulation were measured successfully. Furthermore, the measured stress data was compared with the predicted numerical results of the cure and the thermal stages, independently.@en