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This paper looks at the impact of different application pressure on a phase change thermal interface material (TIM) used on a bare die FCBGA package with a heat sink solution. The application pressure is the key factor in determining the bond line thickness of the material which in turns dictates the performance of the material. To characterise TIM performance at end of package use life at various application pressure, the TIM was subjected to Isothermal Bake accelerated reliability stress. The raw data generated was then extrapolated to use temperatures using statistical models. By fitting the degradation curve in to an Arrhenius type statistical equation, TIM thermal resistance were derived at various application pressure and multiple use temperatures over time. It was observed that for this particular of TIM, thermal resistance saturates at different levels for a certain application pressure. It was found that the impact of pressure on TIM thermal resistance is more pronounced at the end of reliability stresses compared to post assembly. The statistical model indicates that the TIM may have a difference in thermal resistance of up to 45% between high and low pressure application.