Dispensing Thermally Conductive Paste

The hot spot solution

Thermally conductive pastes are high-viscosity potting media with a concentration of special fillers used for effectively dissipating heat between two components. With the establishment of new technologies and the increasing miniaturization of electronic components, the demand for these materials has grown considerably, particularly in recent years. When dispensing thermally conductive pastes, the systems technology must be compatible to prevent damage to the materials and application systems.

Thermally conductive pastes are 1K or 2K paste media with a concentration of conductive fillers. They improve the transmission of heat between two objects, such as between a circuit board and a heat sink, thus helping to prevent drops in performance and faults. These materials are often also described as gap fillers. Usually they are one or two component potting compounds based on silicone, epoxy or polyurethane. Including additives or fillers specifically changes the properties of thermally conductive pastes and adapts them to the particular application.

When using conductive potting materials, their specific thermal conductivity coefficient λ plays an important role. It is often simply described as thermal conductivity or thermal conductance. This value (unit: W/(m∙K)) describes the ability of a material to transfer thermal energy by way of thermal conductance. The higher the thermal conductivity, the greater the heat transfer per unit of time.

Thermally conductive pastes: properties and areas of application

Thermally conductive pastes are used in the automotive industry, in the electronics and electrical industries and in many other sectors. Particularly in recent years there has been a disproportionately high and significant increase in the use of these materials. This is attributed, among other things, to the establishment of new or rapid improvement in proven technologies. Examples of this include LED technology and the encapsulation of batteries for electric mobility. Thermal management is also steadily growing in importance due to the increasing miniaturization of electronic components in all industries.

The thermal conductivity of thermally conductive pastes is established using special fillers such as aluminum oxide, silver or boron nitride. These fillers, which can take the form of irregular fragments, spheres or cubes, often have very high levels of hardness as well as sharp-edged profiles. Therefore, when choosing systems to be used for preparing and dispensing thermally conductive pastes, a compatible system design is absolutely essential. Otherwise the user risks paying high maintenance and repair costs.

Special case: thermally conductive adhesives

Thermally conductive adhesives work on two fronts: While thermally conductive pastes are dispensed to thermally connect two components, thermally conductive adhesives connect components thermally and mechanically. Compared to thermally conductive pastes, the specific thermal conductivity of these adhesives is usually lower. To ensure that the dual role of the material is effective, it is necessary to adjust the filler quantity precisely to the substrate. A higher proportion of filler for improving thermally conductive properties would result in the immediate degradation of the adhesive properties. Conversely, a higher proportion of adhesive runs the risk of the connection loosening due to the effects of temperature.

Thermally conductive pastes: processing and potting

Selecting the right dispensing system is critical to achieving optimum results when applying thermal interface materials. While gear pump dispensers are not suitable for these types of highly filled and paste-like materials, piston-type dispensing systems offer distinct advantages due to their robustness and high precision during the mixing process.

  • Scheugenpflug has improved on its reliable Dos P piston-type dispenser specifically for automated production processes with short cycle times. With the Dos P016 TCA, high-viscosity and high-filler thermally conductive pastes can be dispensed up to three times faster – with consistently high metering accuracy.
    Learn more about the Dos P016 TCA
  • With the newly developed DispensingCell, we offer a compact entry-level solution for thermal management applications. With this fully preconfigured and parameterized system, users profit from short delivery times and an attractive price-performance ratio.
    Learn more about the DispensingCell

1K thermally conductive pastes do not have to be mixed prior to application, but the logistics are more complex compared to 2K systems. Depending on whether the cross-linking is initiated by humidity, UV rays or temperature, different precautionary measures need to be taken to ensure that the material does not begin to cure before its actual use. This may include continual cooling of the material as well as special storage of the drum and cartridges. By contrast, 2K thermally conductive pastes often achieve better material properties than 1K systems, and users benefit from the shorter curing times and reduced VOC emissions.

To achieve the best potting results and prevent system downtimes, users should make sure to utilize system technology that is optimized specifically for such materials when preparing, handling and dispensing the thermally conductive pastes. Scheugenpflug offers two heavy-duty material feed units for the careful feeding of high-viscosity thermal interface material without trapped air.

  • The A220 unit was designed specifically for very pasty potting materials without abrasive fillers. 
    Learn more about the A220
  • The A280 feed unit is recommended when dispensing high-viscosity thermal interface materials that are also highly abrasive.
    Learn more about the A280
TIP: If due to its size the material cartridge needs to be connected to the dispenser using additional material lines, the use of a "booster" may be a good idea. The booster increases the feed pressure, thus also speeding up the dispensing of hightly paste-like thermal interface material.

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