Recent Advances in Thermal Interface Materials

Recent evolution of compactability and integration has become a revolution in electronic device development trends. The quantity of heat created by electrical equipment is steadily growing as their power grows. When two solid surfaces are linked, only a small fraction of the visible surface area will have an actual contact due to roughness in morphology. Modern electrical gadgets are distinguished by high power and frequency, as well as significant heat accumulation.

As a result, Thermal Interface Materials (TIM) are put between two mating surfaces to promote thermal conductance across the interface. Thermal interface materials (TIMs) are critical for efficient heat dissipation to maintain good device functionality and longevity.

As the power of electronic devices continues to grow, so does the amount of heat produced. Thermal interface material (TIM) may effectively increase heat transmission between two solid interfaces and is critical to the performance, service life, and stability of electronic equipment.

 

Ø What Actually are they (TIM) ?

Modern electronic devices, such as light-emitting diodes, integrated circuits and microprocessors, have been advanced with smaller sizes, and a higher degree of integration yet more functions. This generates a significant amount of heat and the devices may become overheated during normal operation. It is of paramount importance to efficiently dissipate the excessive heat so that the devices can perform their function properly at the designed operating temperature.

The TIM is typically made of a material that is compliant and can fill out the voids between the two surfaces, thereby increasing the effective contact area. An ideal TIM would only fill the existing voids in the interface with a thermally conductive material. In a realistic application, the thickness of the TIM will create a gap between the two mating surfaces, but the improvement in thermal conductivity of the TIM compared to the ambient fluid still gives a big improvement in interfacial heat transfer.

Fig. 1 Schematic illustration of a typical electronics package with two TIMs

Thermally conductive PLPs, which include most forms of greases, pads, gels, and PCMs, are the most popular type of TIM. Filler particles significantly improve the heat conductivity of the polymer matrix while keeping wetting and viscosity properties. Because of its broad use in industry, the path from research to the industry is shortened, and new advances can be delivered to the market relatively fast. Although overall performance has not improved significantly in the recent decade, relatively easy experimental methodologies combined with a vast diversity of prospective filler candidates have resulted in a huge number of papers.

Due to the ease of measuring inaccuracies during the application, comparable figures in the literature frequently rely on thermal conductivity rather than thermal interface resistance during operation. Comparisons with other forms of TIM entail simulation of the other parameters of the model. The research given in this review focuses on enhancing thermal conductivity, but it is also crucial to examine other parameters that would influence behaviour in a real-world application, most notably viscosity... 

      The filler fraction, or how much of the composite material is composed of the conducting substance, is another crucial metric to examine in the context of particle fillers. This is especially relevant when comparing study results because while a higher filler fraction obviously leads to better conductivity, it also has significant cost and mechanical characteristics downsides. A notable accomplishment would be to produce a meaningful performance boost with a very tiny filler proportion

Ø How does it works ?

                                                            Fig. 2 Schematic representation of the working principle of a TIM

A TIM-less interface will have a very concentrated heat flux, resulting in a substantial temperature drop at the contact. A TIM fills the gaps and lowers the temperature decrease across the interface.

TIMs are typically used at all interfaces in an electronics package between two solid materials. These interfaces are typically found between the heat-generating die and the integrated heat spreader (IHS), as well as between the IHS and a heat sink. These two TIM applications, referred to as TIM1 and TIM2, are depicted in Fig. 2. Packages with a single TIM linking a die to a heat sink are also available, as a package with more than two TIM instances connecting the chip to the heat sink.

A TIM's thermal performance is often measured by its thermal interface resistance (RTIM), which is a measure of how difficult it is for heat to dissipate across the interface.

According to Fourier's law, it is related to the temperature drop (T) over the interface as T=RTIM Q, where Q is the heat flux. RTIM reduction is a general goal of TIM development. Thermal interface resistance can be broken down into resistive components, which are typically:

where RTIM is the total thermal interface resistance, Rc1 and Rc2 are the contact resistances at the interface between the TIM and the two substrates, is λTIM the thermal conductivity of the TIM and BLT is the bond line thickness, i.e. the thickness of the TIM.

Depending on the type of TIM and application, the various parts of the equation will have a greater or lesser impact on overall performance, therefore it is critical to identify which factors to optimise when selecting or creating a TIM.

In recent years, there has been a strong industry push to reduce RTIM. Because the core and cache are on the same die, the heat transfer from the chip is not uniform. The majority of the power is dissipated from the core, a much smaller area of the chip. Heat flow (q) is non-uniform even within the. core.

Ø Reliability - TIM  

So far, most research on polymeric TIMs has concentrated on the behaviour of freshly produced TIMs. In practice, these TIMs are likely to be subjected to high temperatures and harsh environments throughout the product's lifespan. Assuming a product life of 7 years, this equates to approximately 61, 000 hours of continuous operation or 35, 000 hours for 14 hours each day. If the product operation temperature is 100 °C, the polymers in the TIM are subjected to relatively high temperatures throughout the product's lifetime.

At such high temperatures, polymers deteriorate. However, it is unlikely that these TIMs would be tested for such periods to understand their behaviour when exposed to high temperatures before the product is released. As a result, accelerated lifetime testing is used to better understand deterioration behaviour. The TIM is subjected to substantially greater temperatures than its "use condition" (or operational) temperature during accelerated testing. For example, if the operating temperature of the product is 100 °C, TIM might be tested at 125 °C and 150 °C for considerably less time than the product life.

Ø TIM's Market Trend

The global TIM market is expected to be worth USD 3:4 billion in 2022, rising to USD 56 million by 2027 at a CAGR of 10.5%. The thermal interface materials market is expanding rapidly as a result of rising demand for electronic device downsizing, a growing LED industry, and increased use of TIMs in end-use industries.

This market will experience rapid expansion over the next decade, radically altering the market makeup for TIMs. This expansion is being driven by

(a) an increase in the addressable market, which is essentially the growth in all types of electric vehicles, and 

(b) a high thermal material content per battery pack and, indeed, per kWh deployed. As a result, we expect this market segment to increase from practically zero to more than half of the total market by 2025. This is going to be a significant transition.

• The consumer electronics market is currently the largest market segment. This is due to the comparatively high TIM content per unit, but more crucially, to the huge annual unit sales. 

• TIM is used with the electronics and batteries in this case. Multiple thermal pads connect the EMI shield lid, which covers multiple ICs, to the framework in a typical mobile phone, for example. 

• TIM is used with the electronics and batteries in this case. Multiple thermal pads connect the EMI shield lid, which covers multiple ICs, to the framework in a typical mobile phone, for example.

• TIM's are typically found above or below the CPU, GPU, SSD memory, and batteries in laptops to act as a compact and efficient heatsink. This is a significant market in general, but it will not grow.

• Another big market is telecommunications. TIM is utilised in both the baseband and the remote radio head unit of classic base stations. The baseband unit is often made up of several components such as a baseband processing board, a control board, a power supply, and so on. 

• As LTE stations were rolled out globally in recent years, this was a rapidly developing market. This trend will likely continue as LTE is still being deployed in numerous parts of the world, including China. 

• However, beginning in 2023, this trend will rapidly drop. This is because 5G stations will begin to be deployed in greater numbers. As a result, the potential will shift to 5G systems