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Contact and Heat Transfer Rates with Integrated Circuit Thermal Pads

Key Takeaways

  • Integrated circuit thermal pads are the modem TIM uses to fill the gap between the semiconductor integrated circuit (IC) and the heat sink. It is a progressive thermal management approach that helps achieve optimal cooling. 

  • High thermal conductivity, low thermal resistance, and zero electrical conductivity are the required characteristics of ideal thermal pad material. 

  • Integrated circuit graphite thermal pads are the most sought after thermal interface pad material for CPUs and GPUs.

Thermal pad

A Thermal pad is a TIM used in electronics circuits.

In the electronics industry, one of the main concerns during the design process is thermal management. Only a trusted heat dissipation system can provide unmatched performance and efficiency in electronic circuits. Thermal Interface Materials (TIM) are the key products in the thermal management market, as they are superior in removing heat from electronic components. TIMs such as grease, putties, pastes, phase-change materials, adhesives, and thermal pads assist in the thermal conduction of heat from electronic components such as solid-state switches and integrated circuits to the heat sinks. 

Thermal management of integrated circuits is critical, as a slight rise in temperature can result in malfunctioning or permanent damage. The mass-production of integrated circuits make them cost-effective, but special attention must be paid to their thermal management processes. integrated circuits are manufactured in bulk quantity, leading to manufacturing defects such as unfilled vias, particles embedded between layers, unparalleled pins, and uneven IC surfaces. An uneven  IC surface prevents its firm contact with the heat sinks and reduces the effectiveness of the cooling mechanism. Integrated circuit thermal pads are the modem TIM used to fill the gap between the semiconductor IC and the heat sink. It is a progressive approach to thermal management that helps achieve optimal cooling. 

Enhance the Heat Transfer Rate with Integrated Circuit Thermal Pads

Thermal pad

Thermal pads (shown above) can enhance the heat transfer rate.

(Alt text: Thermal pad) 

The bulk production of integrated circuits leave imperfect surfaces and micro-sized air gaps in the IC surface. The crests and troughs on the IC surface make its coupling with heat sinks improper, and slows down the heat dissipation. To avoid the thermal conduction failures from uneven IC surfaces, Integrated circuit thermal pads and thermal pastes are used. They are thermally conductive materials sandwiched between the semiconductor package and the heat sink. The thermal conductivity of thermal pads and thermal pastes are greater than air and less than metal. Thay act as a conductive path connecting the IC surface and the heat sink. When in operation, the IC surface gets heated and the temperature of the integrated circuit will be more than the TIM and the heat sink. According to the principles of thermodynamics, heat flows from higher temperatures to lower temperatures, and here the flow is from the IC surface to the heat sink via thermal pads or paste. The main intention of using thermal pads and paste is to achieve good thermal contact between the IC surface and heat sink. The TIM also fills the air gaps in the IC surface, enhancing the heat transfer rate in the circuits. 

Thermal paste is a semi-fluid greasy material that fills the holes in the IC surface, whereas the thermal pads are pre-formed flat-surfaced thermally conductive material of defined dimension on to which you can fix your IC, CPU, or GPU. The thermal pads are a modular thermal solution compared to the thermal paste. They are rigid at room temperature but soften when temperatures rise, and they fill the air gap to conform to the mating surfaces.  In thermal paste, you are supposed to guess the amount of paste to be applied. Thermal paste based thermal management is messy and needs clean up after application. It is usually pumped into the heat sink surface or IC surface. Once applied, it is not reusable. 

Considering all these drawbacks to thermal paste, the thermal pad offers top tier thermal performance and establishes effective coupling between the device and heat sink. It is not liquid-based, making it extra durable, reusable, clean, easy to use, and replaceable compared to the thermal paste. The thermal pads are thermally stable and provide electrical isolation. It is also naturally tacky on both sides and does not need any adhesive for placing. Thermal pads perform well and are cost-effective for automotive, defense, aerospace, medical, and consumer electronics. 

Characteristics of Thermal Pads

The characteristics of thermal pads can be classified into electrical, thermal, and physical. The material dimensions and thickness are categorized under physical parameters. We will discuss the electrical and thermal characteristics of an ideal thermal pad:

Thermal Conductivity

Thermal conductivity is the property of material which indicates how efficiently it transfers heat through its body. It is independent of the size and shape of the material. The unit of thermal conductivity is W/m℃. A material of high thermal conductivity is the most suitable for thermal pads.

Thermal Resistance

The thermal resistance of a material varies with the length and cross-sectional area of the material. Its unit is ℃/W. The product of thermal resistance and thermal power gives the temperature difference between the resistance. A low value of thermal resistance makes the thermal pad an ideal TIM. The clamping pressure applied to the material when used as a thermal pad is a factor affecting the thermal resistance. While selecting the thermal pad for applications, the calculation of pressure coming on to the pad can help in choosing a suitable TIM.

Electrical Insulation

Materials offering high thermal conductivity and electrical isolation are required for TIM. Finding materials possessing these two properties is rare. Because of the scarcity of such pure materials, combinations of materials are used for manufacturing thermal pads. Ceramic filled fiberglass, polymers, and silicone rubber are some examples of thermal pad materials.

Commercially Available Integrated Circuit Thermal Pads

Table of thermal pad materials

Table 1: Comparison of commercially available thermal pad materials.

Table 1 compares some commercially available thermal pad materials. From the table, we can see that graphite material has high thermal conductivity with a broad temperature range of operation. IC graphite thermal pads are the most sought after thermal interface pad material for CPUs and GPUs. The graphite pads have replaced the carbon-based viscous thermal paste. The thermal conductivity of graphite is about four times that of the thermal paste, and the procedure of placing the pad is clean and non-messy compared to that of thermal paste. The graphite material possesses conductivity at an intermediate level compared to an insulator and a metal. The electrical conductivity of graphite is enough to create short circuits in motherboards, CPUs, and GPUs. When using the IC graphite thermal pad in electronic circuit boards, one should be careful about its short-circuiting effect. 

Integrated circuit thermal pads are the TIMs that are capable of enhancing the reliability, heat dissipation performance, and thermal contact in electronic circuits. Thermal pads can improve the heat transfer rate in rough, uneven IC surface topography by filling air gaps. The non-viscous texture of thermal pads allows the reuse of the pads. If you are looking for a thermal interface to cool down your  CPUs, GPUs, or motherboards, Integrated circuit thermal pads are the best solution.