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Integrated Heat Spreader (IHS) lids are increasingly being used in flip-chip package technology to enhance power and thermal capabilities. Adequate adhesion of the thermal interface material (TIM) and lid sealant materials are required to not only provide a continuous thermal interface, but also to permit manufacturability. This paper outlines criteria to aid in the material selection process for the first level TIM (TIM1) and the lid sealant to improve its mechanical reliability. It also highlights the importance of understanding the mechanical interaction between the TIM1 and TIM2 layers. A fracture mechanics-based approach is used to provide guidelines for the mechanical properties of the TIM1 and lid sealant material relative to the TIM2. From this modeling, guidelines for lid adhesion strength are defined for a range of package dimensions.