Materials Contributing to Thermal Management in Advanced Semiconductor Packaging (1)

In 3D integrated advanced packages, local hot spots tend to occur as an adverse effect of stacking. These hot spots can lead to performance degradation and reliability concerns.

To mitigate these issues, materials used around CPUs, GPUs, and HBM—areas where hot spots frequently form due to concentrated computational loads—must offer high thermal conductivity and low thermal resistance to efficiently dissipate heat outward.

TIMs fill the microscopic gaps between a semiconductor package and a heat spreader^※1 or heat sink, enabling heat generated by the package to dissipate efficiently. To achieve effective heat dissipation, TIMs must (1) fill surface asperities to reduce contact thermal resistance and (2) exhibit high thermal conductivity.

TIMs are broadly categorized into:

• TIM1: Applied between the package and the heat spreader

• TIM2: Applied between the heat spreader and the heat sink

Because TIM1 is closer to the heat source (the chip) than TIM2, it requires even lower thermal resistance and higher thermal conductivity. Therefore, paste-type TIMs—capable of forming thin layers and incorporating high loadings of high thermal conductivity fillers—are commonly used for TIM1.

Meanwhile, for large-size chips increasingly used in high-performance packages, sheet-type TIMs with high thermal conductivity are applied to ensure reliability.

In data center–grade GPUs, designs that cool packages directly using liquid-cooled heat sinks or cold plates are becoming increasingly common. In these lidless packages, the heat spreader is removed, shortening the thermal path and reducing overall thermal resistance by eliminating one interface.

The TIM used in this structure is placed between the semiconductor package and the heat sink and is referred to as TIM1.5. Similar to TIM1, TIM1.5 requires extremely high thermal conductivity and low thermal resistance; therefore, high-performance paste-type or sheet-type TIMs are used.