When it comes to electronic products, the more power, speed, and functionality jammed into a smaller package, the better. While these products are a dream for end-users, they can be a thermal management nightmare for design engineers. As the power increases, so does the heat. But, because of end-product size limitations, design engineers aren’t able to use larger heatsinks to address the issue of thermal management. In search for an overall efficient, yet compact, thermal solution, more emphasis is being placed on thermal interface materials (TIMs).
TIMs are usually supplied in two forms: solid pads formed with cured silicone rubber, and liquid compounds in the form of greases or pastes. Both types of materials contain a filler that increases thermal conductivity and, while pads are often preferred for their ease-of-use and long-term stability, greases or pastes offer better wetting, which improves overall thermal performance. With greases or pastes, however, there can be trade-offs for the gain in wetting performance. First, these materials can be somewhat messy in a production environment. Additionally, continual thermal cycling of greases can lead to liquid migration, leaving only the filler in place, which eliminates surface wetting and leads to possible field failures. The differing expansion rates of the materials on either side of the interface can create a “pumping” effect, which results in increased thermal impedance and inadequate thermal transfer.
Because they solve some of the problems associated with thermal greases, phase change materials have performed successfully in applications such as telecom base stations, electric trains, consumer electronics, and computers. These materials are used to replace air between the imperfect surfaces of a device and heatsink with a more thermally conductive material that will efficiently transfer heat from the device to the heatsink.
Phase change technology features a wax-based system that is solid at room temperature but becomes liquid once the excess heat of the device pushes the material past its melting point. This versatility provides the engineer with a material that is manufacturing-friendly while also delivering the performance necessary to meet thermal design requirements. Unlike thermal grease, the phase change compound will not migrate or “pump out” of the interface.
One of latest classes of phase-change TIMs is based on the proven platform of phase change technology, but possesses differences that provide a combination of performance and ease-of-use. Previous products featured a coating of phase-change compound applied to an aluminum or polyimide substrate. This generation of products, however, are coated directly onto release liners without the need for a substrate, improving performance. When placed in an interface and pushed past its melting point (45°C) by the electronic component’s heat emission, the compound becomes liquid and flows to fill all gaps and surface imperfections, removing air at the same time. Because there is no substrate to block the flow, the final interface thickness will be as thin as possible and based solely on the geometry of the parts. This thinner interface results in more efficient heat transfer and the spherical aluminum filler ensures heat transfer from the device to the heatsink with ultra-low thermal resistance.
Because the product is offered in a thickness that exceeds that needed to fill all gaps, the pad will generally be somewhat smaller than the area to which it is applied. For example, an application on a 31-mm-square CPU lid would require, depending on the flatness of the heatsink, a square pad between 15 mm and 20 mm. An effect of the smaller dimension is that the force from the retaining screws, bolts, or clips is exerted on a smaller area, which leads to higher pressures and increased flow properties at the compound’s phase change temperature. Due to this phenomenon and the material formulation, low thermal resistance is achieved even at low mounting pressures. This results in reduced stress on the components and limits potential damage to the device.
Phase change technology features a wax-based system that is solid at room temperature but becomes liquid once the excess heat of the device pushes the material past its melting point. This versatility provides the engineer with a material that is manufacturing-friendly while also delivering the performance necessary to meet thermal design requirements. Unlike thermal grease, the phase change compound will not migrate or “pump out” of the interface.
One of latest classes of phase-change TIMs is based on the proven platform of phase change technology, but possesses differences that provide a combination of performance and ease-of-use. Previous products featured a coating of phase-change compound applied to an aluminum or polyimide substrate. This generation of products, however, are coated directly onto release liners without the need for a substrate, improving performance. When placed in an interface and pushed past its melting point (45°C) by the electronic component’s heat emission, the compound becomes liquid and flows to fill all gaps and surface imperfections, removing air at the same time. Because there is no substrate to block the flow, the final interface thickness will be as thin as possible and based solely on the geometry of the parts. This thinner interface results in more efficient heat transfer and the spherical aluminum filler ensures heat transfer from the device to the heatsink with ultra-low thermal resistance.
Because the product is offered in a thickness that exceeds that needed to fill all gaps, the pad will generally be somewhat smaller than the area to which it is applied. For example, an application on a 31-mm-square CPU lid would require, depending on the flatness of the heatsink, a square pad between 15 mm and 20 mm. An effect of the smaller dimension is that the force from the retaining screws, bolts, or clips is exerted on a smaller area, which leads to higher pressures and increased flow properties at the compound’s phase change temperature. Due to this phenomenon and the material formulation, low thermal resistance is achieved even at low mounting pressures. This results in reduced stress on the components and limits potential damage to the device.
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