Thermal Interface Material Introduction

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Thermal Interface Material Introduction

Thermal Greases

Comprised of thermally conductive ceramic fillers in silicone or hydrocarbon oils, a thermal grease is a paste that is applied to one of two mating surfaces. When the surfaces are pressed together, the grease spreads to fill the void. During compression, excess grease squeezes out from between the mated surfaces. Some form of clip or other mounting hardware is needed to secure the joint. Although it is comparatively inexpensive and thermally effective, thermal grease is not an electrical insulator. Another disadvantage is that it can be inconvenient to dispense and apply and it requires cleanup to prevent contamination problems.³ Learn more about our Thermal Grease options.

Cure-in-Place Thermally Conductive Compounds

A thermally conductive compound incorporates thermally conductive ceramic fillers. However, unlike thermal greases, the binder is a rubber material. When first applied, the paste-like compound flows into the interstices between mating surfaces. Then, when subjected to heat, it cures into a dry rubber film. Besides thermal properties, this film also serves as an adhesive, allowing a tight, void-free joint without the need for additional fasteners. Thermally conductive compounds can successfully fill larger gaps in situations where thermal greases might ooze from the joint. Although application and performance is similar to that of thermal grease, cleanup is easier, simply involving removal of the excess cured rubber film.⁴

Thermally Conductive Elastomeric Pads

A thermally conductive elastomeric pad consists of a silicone elastomer filled with thermally conductive ceramic particles and may incorporate woven glass fiber or dielectric film reinforcement. Typically ranging in thickness from 0.1 - 5 mm and in hardness from 5 to 85 Shore A, these pads provide both electrical insulation and thermal conductivity, making them useful in applications requiring electrical isolation. Thicker pads prove useful when large gaps must be filled. During application, the pads are compressed between mating surfaces to make them conform to surface irregularities. Mounting pressure must be adjusted according to the hardness of the elastomer to ensure that voids are filled. A mechanical fastener is essential to maintain the joint once it is assembled.^5,8 View our Thermal Rubber Pads for more information.

Thermally Conductive Adhesive Tapes

A thermally conductive adhesive tape is a double-sided pressure sensitive adhesive film filled with thermally conductive ceramic powder. To facilitate handling, aluminum foil or a polyamide film may support the tape; the latter material also provides electrical insulation. When applied between mating surfaces, the tape must be subjected to pressure to conform to the surfaces. Once the joint is made, the adhesive holds it together permanently, eliminating the need for supplemental fasteners. No bond curing is needed. One limitation of thermally conductive tapes is that they cannot fill large gaps between mating surfaces as well as liquids; hence, the user must trade off the convenience of tape mounting against a nominal sacrifice in thermal performance.⁶ Read more about our Thermally Conductive Adhesives.

Phase Change Materials

Solid at room temperature, phase change materials melt (i.e., undergo a phase change) as the temperature rises to the 104°F to 158°F (40°C to 70°C) range. This makes the material (0.13 mm thick in its dry film form) as easy to handle as a pad, while assuring that it will, when subjected to heat during the assembly process, flow into voids between mating surfaces as effectively as a thermal grease. Ordinarily, applying power to the electronic component introduces the needed heat for phase change to occur, establishing a stable thermal joint. These materials consist of organic binders (i.e., a polymer and a low-melt-point crystalline component, such as a wax), thermally conductive ceramic fillers, and, if necessary, a supporting substrate, such as aluminum foil or woven glass mesh.⁷ Learn about our Phase Change Materials.

Where to Obtain or Learn More about Thermal Interface Materials

Review our Thermal Interface Material Solutions or some of the other resources we have on TIMs:

References:

¹de Sorgo, Miksa, "Thermal Interface Materials", ElectronicsCooling Magazine, Sept. 1996.

²Orcus Technical Information

³Hanson. Kevin, "Thermal Isolators, Material Properties that Determine Electrical, Mechanical, and Thermal Performance", PCIM Magazine, April 1999.

⁴de Sorgo, Miksa, ibid.

⁵de Sorgo, Miksa, ibid.

⁶de Sorgo, Miksa, ibid.

⁷de Sorgo, Miksa, "Understanding Phase Change Materials", ElectronicsCooling Magazine, May. 2002