In the thermal design and assembly stages of electronic devices, the selection of thermal interface materials (TIMs) directly affects system thermal resistance, temperature stability, and long-term reliability. Thermal pads and thermal pastes, as common types of TIMs, are widely used in industrial robots, industrial PCs, RF power supplies, scientific cameras, and other equipment. However, the two are not fully interchangeable. Properly distinguishing material forms, thermal conduction mechanisms, and their applicable operating ranges helps reduce interfacial thermal resistance, mitigate the risk of high‑temperature alarms, and enhance the long-term operational stability of equipment.
 

I. Functions and Selection Criteria for Thermal Interface Materials
 

The core function of thermal interface materials is to fill the microscopic gaps between the heat source and the heat‑dissipating structure, thereby reducing interfacial thermal resistance. At the microscale, metal contact surfaces typically exhibit a certain degree of roughness; even after precision machining, minute irregularities and voids may remain. The air trapped in these gaps has poor thermal conductivity and can impede heat transfer. By replacing the air layer, thermal interface materials enable more continuous heat conduction from the heat source to the heat‑dissipating structure.

However, the applicable conditions vary among different thermal interface materials. Selection of thermal interface materials and thermal grease, A comprehensive assessment is required, taking into account surface flatness, gap height, vibration conditions, insulation requirements, maintenance and disassembly needs, and long-term thermal‑stability performance; a single comparison based solely on thermal conductivity is insufficient.
 

II. Characteristics and Applicable Scenarios of Thermal Grease

Thermal grease is a fluid or semi-fluid thermal interface material, primarily composed of thermally conductive fillers and an organic carrier. Its fluidity enables it to conform well to the microscopic irregularities of contacting surfaces, filling minute gaps and thereby reducing interfacial thermal resistance. For chip packages with flat, highly rigid, and relatively stable contact pressures, thermal grease can establish a more continuous thermal conduction path.
 

Thermal grease excels in its strong interface‑adhesion capability, making it well suited for applications where the mating surfaces are highly planar. For example, in the assembly of certain domestically produced CPUs and AI accelerator cards, where the heat source and the cooling structure are relatively flat, thermal interface material such as thermal grease can be used. However, during application, it is essential to control the coating thickness to prevent excessive thermal resistance caused by an overly thick layer.
 

At the same time, thermal paste also has certain limitations. On the one hand, it typically lacks significant elastic compensation, making it difficult to accommodate substantial height differences. On the other hand, under prolonged high-temperature operating conditions, certain thermal pastes may undergo compositional changes, dry out, or experience oil separation, thereby degrading interfacial performance and potentially affecting adjacent components. Consequently, thermal paste is best suited for applications involving flat, tightly bonded interfaces with low maintenance requirements.

III. Characteristics and Applicable Scenarios of Thermal Conductive Pads
 

Thermal interface material is a flexible, solid-state thermal pad typically composed of thermally conductive fillers embedded in a polymer matrix. It has a certain degree of compressibility and resilience. Its structural characteristics ensure that it not only conducts heat but also absorbs certain mechanical stresses, compensates for height differences between components, and provides cushioning under vibration or impact conditions.
 

Thermal interface materials are well suited for applications involving components with uneven heights, irregular contact surfaces, or equipment that requires frequent maintenance and disassembly. Some thermal interface materials also offer a degree of electrical insulation, enabling them to meet both thermal‑conductivity and electrical‑isolation requirements in certain designs. As solid‑state, molded materials, they typically do not exhibit significant leakage, thereby minimizing their impact on components surrounding the circuit board.
 

However, thermal interface materials also have their application limitations. Under the same thermal conductivity, the interfacial thermal resistance of such materials is typically influenced by thickness, compression ratio, contact area, and surface flatness. For chip‑level thermal management applications that demand extremely tight gaps, high contact pressures, and ultra‑low interfacial thermal resistance, thermally conductive pads may not be the most suitable choice.
 

IV. Comparison of Thermal Pads and Thermal Grease Selection

From the perspective of structural compatibility, Thermal grease is better suited for flat, hard-to-hard, tightly contacting interfaces, while thermal pads are more appropriate for applications involving height differences, vibration, electrical insulation, or frequent disassembly and reassembly. From the perspective of thermal resistance performance, Under optimal application conditions, thermal interface materials can achieve low interfacial thermal resistance; however, their performance is significantly influenced by coating thickness and surface condition. In contrast, thermally conductive pads exhibit relatively stable thermal resistance, but their thickness and compression ratio must be carefully selected.
 

From the perspective of reliability and maintenance, Thermal grease is better suited for interfaces that are sealed, stable, and require minimal disassembly; thermal pads, on the other hand, are more appropriate for applications involving cushioning, electrical insulation, or frequent reassembly. In practical engineering applications, The two approaches are not always mutually exclusive; for certain complex devices, thermal grease and thermal pads can be employed separately, depending on the structural constraints at different locations, thereby enabling a zone‑based thermal design.

Figure 1 Schematic diagram of the thermal conduction mechanism at the thermally conductive grease interface.
 

V. Combined Design Approaches in Industrial Applications

In devices such as industrial robots, industrial PCs, RF power supplies, and scientific cameras, the types of heat sources are often quite complex. The contact conditions among the chip core, power modules, heat-sink baseplates, and the enclosure structure are not entirely uniform. Therefore, The selection of thermal interface materials should be based on a comprehensive assessment of the heat source’s gap, surface condition, vibration level, temperature‑resistance requirements, and maintenance strategy.
 

For the flat interface between the chip core and the heat sink, if the structure permits and maintenance requirements are low, thermal grease should be prioritized to reduce interfacial thermal resistance. For areas with peripheral components, devices of varying heights, or conditions involving vibration, thermally conductive pads can be used to compensate for height differences and provide cushioning. In certain highly integrated devices, thermal grease and thermally conductive pads can each assume distinct thermal‑management roles at different interfaces, thereby forming a synergistic cooling solution.

Figure 2: Schematic comparison of thermal pads and thermal pastes for selection

Thermal pads and thermal paste serve distinct roles in thermal design and should not be used interchangeably.
Thermal grease is best suited for flat, tightly coupled chip‑to‑substrate interfaces with minimal gaps, whereas thermal pads are more appropriate for applications involving height differences, vibration, electrical insulation, or frequent disassembly. In engineering practice, the choice should be guided by the interface condition, target thermal resistance, mechanical constraints, and long‑term reliability requirements; when necessary, a hybrid approach may be adopted to enhance overall thermal performance and operational stability.

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