Thermally conductive pastes with a high thermal conductivity of 7.0 W/mK demand for high standards of material preparation and metering technology.
Keeping power electronics cool
Electronic components are becoming increasingly powerful and smaller. The heat generation per area in electronic components is becoming steadily higher as a result of progressive miniaturization. In order for these components to achieve a long service life and trouble-free operation, the heat generated must be dissipated efficiently. This is achieved either by complex active cooling with a medium (air, coolant) or by connecting a passive heat sink with thermal paste.
Thermal conductive pastes are pasty 1C or 2C media, which essentially consist of a polymer matrix formulated with a thermally conductive filler. This enables efficient heat transfer and gap bridging between the heat source (electronic components) and the cold depot (housing or cooling medium). The polymer matrix (often consisting of silicone, epoxy or polyurethane) holds the filler in place after curing. Over the component lifetime, there are no longer any insulating air gaps that would interfere with heat transfer.
Compared to solid pads (also called GapPads) or films, thermally conductive pastes offer the advantage that they adapt optimally to the individual contours of the component and can therefore be used more flexible. Air gaps are prevented and thermal conductivity is increased.
The thermal conductivity is determined by the thermal conductivity coefficient λ (W/mK). The higher the value, the more heat can be transferred per unit of time. There are materials today which have conductivity values of over 7 W/mK.
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Applications and requirements
Thermal conductive pastes are used wherever electronic components need to be cooled efficiently and disruptive ambient conditions must be completely eliminated. The automotive and electrical industries, as well as numerous other sectors, use the ability of thermal conductive pastes to efficiently dissipate the heat generated from power electronics. A common application is increasing energy densities in batteries in the field of electromobility, as well as for other moblity applications.
As the demands on thermal conductivity continue to rise, a higher proportion of filler is increasingly being introduced into the formulation. These fillers are optimized by the material manufacturers in terms of their particle size distribution and geometric surface properties for efficient heat transfer. The insulating property of the surrounding plastic should exert as little influence as possible on the thermal conductivity. Typical fillers for thermally conductive pastes are aluminum oxide and boron nitride, which are also used in grinding pastes due to their hardness grades. In addition to the ceramic filler classes, formulations with metal particles are also used, especially in applications that require electrical conductivity at the same time.
In addition to the polymer matrix and the fillers, special additives are used to control the rheological properties and the wettability of the fillers. These influence the function as well as the processability of the formulation. The low proportion of polymer matrix in the presence of fillers, some of which are highly abrasive, poses particular challenges for the system design and the dispensing components used. High maintenance costs and plant downtimes must be avoided.
Thermal conductive pastes must be processed without wear on components of the dispensing system, where possible.
Processing of thermal conductive pastes
Thermally conductive pastes, regardless of whether they are used as 1K or 2K systems, pose fundamental challenges for the metering technology used. One is the abrasiveness of the fillers, which must be processed without wear on the components of the dispensing system. The other is the low proportion of polymer matrix, which tends to separate from the filler component of the formulation under high pressure and mechanical stress.
bdtronic has been successfully using eccentric screw pumps for the application of thermal conductive pastes for years. Compared to other pump systems, it offers several advantages due to its robust and low-wear technology. Gear pumps quickly reach their wear limit with such highly filled materials. Piston metering pumps, on the other hand, often require laborious and lengthy maintenance due to their complex design.
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