The application and injection of TIMS or gap fillers on and into battery modules or other electronic components in electric vehicles (EVs) requires an absolutely process-safe handling of 1- or 2-component materials.
Precise, fully automated, easily adjustable and endless dosing is the prerequisite. Purely volumetric dispensing systems like ViscoTec dispensers enable exactly that: continuous, repeatable, material-friendly dispensing of TIMs, gap fillers, sealing materials and adhesives – regardless of their viscosity. A specially developed rotor in the ViscoTec dispensers ensures long service life, even when using highly abrasive materials. For example, a long-term test with a two-component gap filler, with aluminium-oxide fillers, showed a nine-fold service life compared to the standard rotor. By using a special coating on the rotors or more specifically by using a ceramic rotor, customers can achieve even greater process stability due to a much longer lifetime of the dispenser components.
Battery cell assembly
The thermal connection of the electronic modules or battery modules to the heat sink is crucial to dissipate the generated heat via the heat sink and therefore prevent overheating. For this purpose, heat-conducting pastes and adhesives with increasingly higher thermal conductivities are used to eliminate the air gap.
Up until now, the usual heat-conducting pastes only had thermal conductivities of 0.8 to 2.0 W/mK. Thanks to higher proportions of thermally conductive solid particles and the specific selection of particle size distributions and different filler types, values of up to 7 to 8 W/mK have now been achieved.
These mostly ceramic fillers, such as aluminium oxide or aluminium nitride, have a remarkably high thermal conductivity combined with electrical insulation. However, due to their high Mohs hardness of up to 9 or 10, they are generating challenges for the dispensing technology with regard to wear and maintenance intervals.
These highly filled materials must be dosed without bubbles. Only then optimum thermal conductivity can be guaranteed. However, implementation is made more difficult because the liquid gap-filling material is applied in large quantities. In addition, the material is very abrasive, and the dosing system can wear out quickly.
Nevertheless, in order to significantly increase the service life of the dispensing components, the proven stainless-steel rotor has been further developed through the use of special coatings based on Diamond Coating.
More specifically, a new type of rotor, made from a technical full ceramic, revolutionises the volumetric dispensing of heat conducting pastes: in numerous internal long-term tests as well as field tests carried out in existing customer systems, a clear optimisation could be demonstrated. The special coating can already double or triple the service life of the core components. However, according to current experience, the ceramic rotor version achieves a service life of the core components that is approximately 9 to 10 times longer.
The various long-term tests with running times ranging from several months to over a year and dispensed material quantities of several hundred to thousand liters show hardly any signs of wear on the ceramic rotor to date. A stable and process-safe dispensing is still possible, which makes a much longer period of use conceivable. Therefore, the cost-in-use can be significantly reduced.
“Fight fire with fire – this is the motto of the ceramic rotor,” says Manuel Paintmayer, Relationship Manager – Material Manufacturing at ViscoTec. “Due to the three to four times stronger surface hardness compared to the previous hard chrome-plated stainless steel version of the rotor, long-term tests with state-of-the-art gap fillers have not yet shown any measurable wear or damage to the surface of the ceramic rotor.”
The counterpart to the rotor in the dispenser is the stator, which is made of special elastomers. The stators also have a much longer service life thanks to the undamaged surface of the rotor.
Ceramic rotors for shot sizes from 50µl showed no signs of malfunction or wear after more than 100 litres of dispensed gap filler. This corresponds to more than 2,000,000 individual shots. Identical results were shown for larger dispensers with shot sizes from 1.7ml. After more than 4,000 litres of dispensed material, no signs of wear on the rotor could be measured and precise and stable dispensing was still possible. These results were even achieved by using one single stator only.
The use of ceramic rotors therefore results in numerous advantages for customers:
- Maximum process reliability through unchanged dispensing precision of the volumetric dispensing system.
- Minimal set-up and downtime.
- Cost reduction due to minimal spare parts requirement and minimal cost in use.
- Easy to integrate into existing systems.
ViscoTec has achieved its goal of the highest quality and greatest process reliability. Customers are enthusiastic, as shown by one who remarked: “The dispensing system did not have to be recalibrated once during a complete production year in order to compensate for possible wear and tear.”