Non-Destructive Evaluation of Thermal Interface Materials using Modulated Heating of Selective Cores

Thermal interface material (TIM) performance can be affected by various defects occurring in the TIM layer like voiding, dry-out, pump-out, where the thermal resistance increases, leading to damage/failure of the chip package. Here the focus of the proposed method is to detect the shift in the change of thermal properties for the TIM layer between the silicon die and the internal heat sink (IHS), usually referred to as TIM1. This novel method utilizes the loading of the CPU core by using software stressors to induce an oscillating temperature response in the chip package. The temperature response generated from the periodic heat source is dependent on the thermal diffusivity (α) of the material layers in the chip package. The changes in thermal properties of the TIM1 layer alter the temperature response; this alteration is depicted using the computational study for different chip parameters. The primary method of detecting the temperature response characteristics is based on monitoring and measuring the current consumed by the chip package. The current oscillates as per the requirement of the processing load due to the use of software stressors. This variable computational load leads to changes to the temperature, altering the leakage current, as the leakage current in a transistor is dependent on the temperature. The periodic leakage current of the chip package allows us to predict the thermal properties in the TIM1 layer. Neighboring cores can be evaluated simultaneously with minimal thermal crosstalk by operating at different frequencies that are separated, via signal processing. Experiments on a commercial off-the-shelf package will be discussed.