The Role of Thermal Interface Material in Modern Electronic Devices

Introduction: What is TIM, and why is it important?

TIM is a substance inserted between two components – typically a heat-generating device and a heat sink – to improve thermal conductivity and heat transfer. In electronic devices or systems, air gaps or voids often exist between interfacing components due to surface roughness, manufacturing imperfections, or misalignment during assembly. These air gaps can lead to low thermal conductivity compared to most solid materials, increasing thermal resistance and causing poor heat dissipation, localized hotspots, overheating, or potential device failure.

Modern electronics are increasingly advanced and compact. More components in a limited space mean more power and more heat. Thermal management is essential for device reliability and performance, but implementing it effectively can be a challenge. TIM acts as a critical thermal path, designed to dissipate heat from the device to the spreader or heat sink by filling air gaps and improving thermal contact between interfacing surfaces. The result is effective cooling for devices.

Diagram Description: A microscopic view of two rough surfaces with thermal interface material filling the gaps to improve contact and heat transfer.

What Applications Are Driving TIM Requirements?

There are three segments in two markets for TIM based on the most common application and point of use. TIM 1 is typically installed between the top of a bare flip chip die and an applied flip chip lid in semiconductor packaging. TIM 1.5 and TIM 2 are often used in PCB and systems assembly. TIM 1.5 is installed between the top of a bare flip chip die and a heat spreader, heat sink, or heat pipe for a no-lid design. TIM 2 is installed between a packaged semiconductor and a heat sink or between a module and a secondary heat sink or heat spreader.

Diagram Description: Schematics showing TIM application in electronic packages: TIM 1 is placed between the chip (or die) and the integrated heat spreader. TIM 2 is placed between the IHS and the heat sink; TIM 1.5 is placed between the chip and the heat sink.

What Types of TIM Are Available?

Liquid TIMs

• Thermal grease/paste: Original, non-fabricated TIM frequently used for high-end applications due to superior thermal performance, and for low-end applications due to potential low cost.
• Gel: Non-fabricated TIM applied like grease but cured-in-place or precured to yield a loosely cross-linked material with a low modulus. Considered a type of grease.
• Liquid adhesive: Thermal adhesives provide mechanical attachment between a heat-generating part and a heat sink after a cure step.
• Liquid gap filler: Dispensable material that can be pre-polymerized or supplied as a two-part solution that cures; designed to displace gap filler pads.

Solid TIMs

• Phase change: An easy-to-apply replacement for thermal grease that is solid at room temperature but softens and becomes a liquid at the device's operating temperature.
• Gap filler pads: Thick, compliant sheet materials used to fill large gaps between heat-generating components and a heat sink.
• Tape adhesives: Thermally conductive pressure-sensitive adhesive (PSA) tape provides mechanical attachment between heat-generating components and a heat sink.
• Films: Thermal material that provides electrical insulation between a heat-generating component (e.g., a power semiconductor) and a heat sink.

What Are the Key Considerations When Selecting TIMs?

• Overall thermal performance: TIMs' primary function is to enhance heat transfer. High thermal conductivity and lower thermal resistance are recommended for efficient heat dissipation. Typical values range from 1-10W/mK or higher for high-performance applications.
• Operating temperature range: TIMs must function effectively within the application's temperature range.
• Material characteristics: TIMs must maintain integrity and performance under mechanical stress. Properties like hardness, compressibility, and flexibility should be evaluated. Electrical insulation may be necessary, requiring avoidance of electrically conductive TIMs.
• Reliability and longevity: TIMs should maintain performance over a device's lifespan, considering long-term stability, thermal cycling resistance, and potential degradation.
• Processing and manufacturing characteristics: Consider the impact on production processes, including compatibility with automated processes, ease of integration, rework ability, and quality control.
• Cost: Cost-effectiveness is critical for large-scale manufacturing. Balance performance with cost for target applications.
• Environmental and safety: Choose non-toxic and non-flammable materials to comply with environmental regulations and safety standards.

What Role Does Thermal Conductivity Play in TIMs?

A material's ability to conduct heat is called thermal conductivity. It is an intrinsic property, independent of shape or size. Materials that deliver high thermal conductivity are ideal for thermal management.

The formula for thermal conductivity (K) is: K = Qd / AΔT, where:

• K = thermal conductivity
• Q = amount of heat transferred
• d = distance between the two isothermal planes
• A = area of surface
• ΔT = difference in temperature

Thermal Impedance

Thermal impedance is a measure of the sum of thermal resistance and thermal contact resistance of a material.

Thermal resistance (R₀) is a thickness-dependent property and can be calculated by: R₀ = L / kA, where:

• k = thermal conductivity [W/mK]
• L = plane thickness [m]
• A = plane area [m²]

The Total Thermal Impedance (R)

The total thermal impedance (R) is given by: R = RC1 + R₀ + RC2, where:

RC1 and RC2 represent the contact resistance between the upper surface and TIM, and the lower surface and TIM, respectively.

Factors impacting overall thermal impedance include material hardness, viscosity, bond line thickness, and surface wetting capability. Applying contact pressure requires the TIM to be flexible enough to conform to surface asperities while maintaining a small bond line thickness, low contact resistance, and good bulk thermal conductivity.

Diagram Description: A diagram illustrating heat flow from an electronic package through a thermal interface material to a heat sink, showing the components of thermal resistance (RC1, R₀, RC2) and temperature gradient along the distance.

What Types of TIM Does Honeywell Offer?

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Choose Your Phase Change Material

Note: The checkmark symbol (✔) in the 'Fast Drying Type' column indicates that the product is fast drying.