Material

Thermal Interface Materials

Engineered silicone elastomers capable of conducting heat efficiently to extend the service life of sensitive electronics

Green, pink, and blue thermal gap pad gaskets

Thermal interface materials (TIMs) transfer or dissipate heat in electronic devices and equipment. They use silicone as the base elastomer and contain specialized fillers that impart thermal conductivity. Normally, silicone is thermally insulating; however, the addition of thermally conductive fillers enable TIMs to move heat instead.

Thermal Interface Materials: The Stockwell Advantage

Stockwell Elastomerics sources thermal interface materials from leading suppliers and fabricates thermal gap filler pads that bridge the air gaps between heat sources and heat sinks. Stockwell Elastomerics uses die cutting, flash cutting, and waterjet cutting to fabricate Saint-Gobain ThermaCool® Gap Fillers, Polymer Science P-THERM® Silicone Gap Fillers, and 3M materials.

These manufacturers produce thermal pad materials with various physical properties such as thickness, thermal conductivity, dielectric strength, availability of coated fabric surface on one side and hardness (Shore 00). Stockwell Elastomerics’ Applications Engineers are adept at working with customers to select the best material for specific applications.

Saint-Gobain produces Thermacool Gap Fillers TC3006, highly compliant, 1.1 W/m-K), TC2006, compliant, 1.6 W/m-K) and high performance TC-3008, 3.0 W/m-K in 24″ x 24″ sheets to provide opportunities for best yield and production economies. Saint-Gobain’s sheet sizes support excellent part yield and larger thermal pad sizes. Standard sheet thicknesses range from .020″ to .200″. Stockwell Elastomerics maintains a broad inventory of these materials in thicknesses ranging from .020″ to .250″ thick to support needs for fast-turn initial production. Available grades include:
- TC-3006: highly compliant, 1.1 W/m-K
- TC-2006: compliant, 1.6 W/m-K
- TC-3008: high performance, 3.0 W/m-K
Polymer Science offers a variety of thermally conductive gap filler pad materials designed to achieve desired heat management properties, including some semi-low compression set gap fillers and some ultra-soft gap fillers. Polymer Science manufactures P-THERM® Silicone Gap Fillers in continuous lengths that are 18″ wide. The P-THERM materials include the PS-2505 (5.0 W/m-K) gap filler, PS-1543 (3.0 W/m-K), and PS-1541 (1.0 W/m-K) gap fillers, among others. The 18″ wide continuous length allows for many options in cutting techniques and good material yield. Polymer Science P-THERM® gap fillers are made in the USA, ensuring a reliable supply chain. Available options include:
- PS-2505: 5.0 W/m-K
- PS-1453: 3.0 W/m-K
- PS-1541: 1.0 W/m-K
3M – Stockwell Elastomerics is a 3M Preferred Converter that can also source, stock, and cut 3M thermally conductive silicone interface pads. Contact Stockwell Elastomerics for more information.

Stockwell Elastomerics can also apply thermally conductive adhesives (or other stronger adhesives) to thermal pad installation. In addition to gap fillers, these suppliers make thermally conductive silicone coated fabrics, thermally conductive tapes, and thermally conductive solid silicone materials. Some thermal gap filler materials are supported with a thermal fabric or thermal film.

Visit the Thermally Conductive Materials Data Sheets page for detailed technical information on these materials.

Visit the Thermal Gap Filler Pads page for information on the thermal gap pads manufactured by Stockwell Elastomerics using these thermal interface materials.

High Heat and Thermal Pads

Electronic devices inherently generate heat, the enemy of reliable electronics. When designers add more numerous and increasingly powerful components to electronic assemblies, the added heat that’s generated can reduce the capacity, lifespan, and performance of printed circuit boards (PCBs), solder joints, and components.

Thermal interface materials extend the life, performance, and reliability of electronics by transferring heat so that it can be removed from electronic enclosures by cooling mechanisms such as fans. Some TIMs have UL 94 flame ratings.

Heat Sources and Heat Sinks

TIMs are installed between heat-producing devices such as integrated circuits (ICs) and heat-dissipating devices such as metal heat sinks. PCBs and PCB components have uneven surfaces, however, so thermal interface materials need to be conformable so that they fill the tiny air gaps between heat-generating and heat-dissipating components. Otherwise, air trapped between a heat-producing device and a heat sink inhibits the effective transfer of heat away from hot spots to the exterior of a closed system. Air has a significantly higher thermal resistance than TIMs, which also have a higher thermal conductivity than air.

Thermal Conductivity vs. Heat Transfer

Stockwell Elastomerics carries a variety of thermal interface materials, which are often characterized by their thermal conductivity values. This is very helpful in comparing one material to another but cannot always predict how a material will perform. Actual heat transfer in an application depends on factors like:

Compressed thickness
Surface “wetting”
Temperature difference
Surface cleanliness

A softer material with moderate thermal conductivity can often perform better than a firm material with high thermal conductivity. Stockwell Elastomerics’ Applications Engineers can help determine which thermal pad material will work best for a customer’s unique need.

There are other considerations as well. Thermal resistance is a measure of the opposition to the flow of heat. It’s the reciprocal of thermal conductivity and typically measured in Kelvin per watt (K/W). In PCB circuit design, thermal resistance is used to measure a package’s heat dissipation and to avoid overheating. When comparing a thermal gap pad with a lower TC and to one with a higher TC, the product with a lower TC could be preferable if its thermal resistance is lower and the material has better wet-out.

Stockwell Elastomerics’ Applications Engineers can help determine which thermal pad material will work best for a customer’s unique need.

Thermal Conductivity and Air Gaps

Thermal conductivity, a measure of heat transfer, is a key TIM specification that is expressed in Watts per meter Kelvin (W/m•K). Although thermal interface materials have a much higher thermal conductivity than air, they have a significantly lower thermal conductivity than the metals that are used for heat sinks. Solid metals won’t conform to uneven surfaces, however, and they’re not compressible like thermal interface materials. Thermal conductivity is dependent upon compressed thickness, and thermal interface sheet materials come in a range of thicknesses.

TIM Thickness and Thermal Management

By providing a conformable thermal path between a heat source and a heat sink, TIMs support effective thermal management systems that include heat sinks and fans. Yet, high thermal conductivity alone is an incomplete basis for TIM selection. Interfacial thickness, the contact surfaces, and the pressure applied between a heat-generating component and heat sink are also factors to consider. In general, however, thinner gap fillers are used to improve the efficiency of finned heat sinks and thicker gap fillers are used to conduct heat to chassis or enclosures.

Thermally Conductive Materials

TIMs are not the only thermally conductive materials used by the electronics industry, but they’re an easy-to-apply alternative to messy thermal greases and thermal pastes. The thermally conductive materials that Stockwell Elastomerics fabricates include thermal gap fillers, a category of products that are also known as thermal pads, gap pads, and gap filler pads. Most of the gap fillers that Stockwell Elastomerics fabricates are sheets of very soft or ultra-soft silicones with a dough-like consistency; however, thermally conductive silicone sponge can also be used for gap pads.

In addition, Stockwell Elastomerics fabricates the following types of thermally conductive materials.

Thermally conductive silicone coated fabrics
Thermally conductive tapes
Thermally conductive solid silicone

TIMs also include phase change materials (PCMs) that absorb and release thermal energy when they change from one state of matter to another, typically from a solid to a liquid or vice versa. Contact Stockwell Elastomerics to discuss development projects with phase change materials.

Very Soft Silicones for Thermal Gap Filler Pads

Thermal gap filler pads are made from a silicone polymer that is filled with ceramic particles. Normally, polymers are not good conductors of heat; however, the addition of ceramic particles (such as aluminum oxide) produces compounds with higher amounts of thermal conductivity. Depending on the specific thermal interface material that Stockwell Elastomerics fabricates for gap pads, thermal conductivity can range from 1.0 to 5.0 W/m-K.

Most of the thermal pads that Stockwell Elastomerics cuts from sheet materials are made of silicone with a gel-like modulus. Unlike a cured silicone rubber, this material is very soft and compliant. Generally, thermal gap fillers are intended to be compressed only once, when PCB components are installed. Therefore, they do not rebound well. However, thermally conductive silicone sponge (see next section below) rebounds after being compressed and can be recompressed many times. Silicone gap fillers from Stockwell Elastomerics can be provided in a variety of manufactured configurations. Parts can be cut into intricate shapes using waterjet cutting technology, provided kiss cut onto card stock backing, or in sheet or roll stock format.

Thermally Conductive Sponge for Thermal Gap Filler Pads

Stockwell Elastomerics also fabricates thermal management products from NORSEAL® (formerly COHRlastic®) R10404M green heat-conductive rubber. This cured thermal interface material is a closed cell silicone sponge and differs from other thermal gap fillers because it rebounds after being compressed and can be recompressed many times.

NORSEAL R10404M is five times more thermally conductive than standard silicone sponge. Another thermally conductive silicone sponge material, R10404, is also available but has a lower thermal conductivity than R10404M. Applications for R10404 include heat press pads, thermal pads for heat sinks, gaskets and cushioning pads.

R10404M thermally conductive silicone rubber is available in thicknesses that range from 0.32″ to 0.188″. Continuous rolls are 36″ wide. Sheets are 36″ x 36″ with a .250″ thickness. Stockwell Elastomerics can apply thermally conductive adhesives to these materials and supply customers with sheets or die cut or waterjet cut parts.

Thermally Conductive Gap Pads Video Demo

The video below is a visual representation of how thermal gap fillers work. A TC-3008 thermal pad is applied to bottom of one beaker while the other is place directly onto a heat source. The thermal gap filler conforms to the irregularities between the surface which eliminates air pockets and creates a thermal bridge; this in turn allows more energy to transfer to the water. The beaker with the gap filler boils more quickly than the beaker without the pad. (Note: This video is a visual example and not the intended use for thermal gap fillers.)

https://www.youtube.com/watch?v=7_PlgDg6eJg

Thermal Gap Filler Pads Demo (https://www.youtube.com/watch?v=7_PlgDg6eJg)

Frequently Asked Questions about Thermal Interface Materials

What are thermal interface materials and why are they used?

Thermal interface materials (TIMs) are silicone‑based materials that transfer heat away from electronic components. Silicones are inherently thermally insulating, but the addition of ceramic fillers makes them thermally conductive instead. TIMs are used to remove heat from electronics because high temperatures can degrade or damage sensitive components.

How do thermal interface materials work?

TIMs work by eliminating tiny air gaps between a heat-generating component such as a chip and a heat-spreading surface such as a heat sink, chassis, or cold plate. Air is a poor thermal conductor, so even small voids dramatically increase thermal resistance. This prevents heat from dissipating away from sensitive electronic components. TIMs conform to surface irregularities and displace trapped air to create a continuous, lower-resistance thermal path.

What is thermal conductivity and how is it measured?

Thermal conductivity (TC) is a material property that describes how efficiently heat flows through a solid. It’s expressed in watts per meter Kelvin (W/m·K). A higher value means the material transfers heat more efficiently. Most TIMs have thermal conductivity values ranging from 1.0 to 5.0 W/m-k, depending on the filler system.

How important is thermal conductivity during TIM selection?

Engineers use thermal conductivity as a comparison metric, but actual heat transfer depends on compressed thickness, surface wet-out, contact pressure, and surface cleanliness. A softer material with moderate thermal conductivity can outperform a firmer, higher-TC material that has better wet-out and less thermal resistance if it better conforms to the application.

Why is thickness important with thermal interface materials?

Thicker materials must conduct heat along a longer path, which increases thermal resistance even if the material has a high thermal conductivity. Ultra-soft TIMs can compensate by compressing significantly, but the final compressed thickness (and not the nominal thickness) is what determines actual heat transfer performance.

Who makes thermal interface materials and what types are available?

Stockwell Elastomerics sources thermal interface materials from Saint-Gobain, Polymer Science (P-THERM™), 3M, and Henkel Berquist. Types of TIMs include thermal gap filler pads, thermally conductive silicone sponge, thermally conductive tapes and coated fabrics, thermally conductive solid silicone, and phase-change materials.

How do thermal gap filler pads compare to thermal greases?

Thermal greases are messy and time-consuming to apply. Thermal gap filler pads are tacky for easy placement, and they can be cut into custom shapes that accommodate complex geometries. These Pads , as they are also known, provide stable performance over time and are widely used as grease replacements.

What makes ultra-soft gap fillers different from standard silicone pads?

Ultra-soft gap fillers such as P-THERM™ PS-1541, PS-1543, and PS-2505 have a gel-like modulus that flows and conforms to surface irregularities, requires very low compression force, and achieves excellent wet-out. They’re ideal for tolerance stack-ups and height variations. Ultra-soft gap fillers are usually compressed only once. They do not rebound like a sponge.

When should engineers choose thermally conductive silicone sponge instead of gap fillers?

Use silicone sponge when repeated compression is required and the application needs a rebounding material that provides both a gasket and a thermal path in one component. NORSEAL™ R10404M is a thermally conductive closed-cell silicone sponge that’s used for battery pack thermal management and with power electronics or heat-spreading interfaces.