What is special about WACKER thermal paste? And what is the link regarding abrasiveness? Which challenges appear for the dosing technology with these materials? A lot of questions were answered in an interesting interview: Franz Kamhuber from ViscoTec in a conversation with Dr. Markus Jandke, Technical Manager Electronics Industrial Solutions Business Unit Engineering Silicones at WACKER.
Dr. Markus Jandke
Franz Kamhuber
WACKER is a globally operating chemicals group. With around 17,000 employees and an annual revenue of around € 5.3 billion (2015). The company has 25 production sites, 21 technical competence centers and 52 sales offices worldwide. WACKER is divided into four business areas: WACKER SILICONES, WACKER POLYMERS, WACKER BIOSOLUTIONS and WACKER POLYSILICON. Finally WACKER SILICONES is the largest business unit and is one of the top 3 manufacturers of silicones worldwide.
The chemical giant and ViscoTec Pumpen- u. Dosiertechnik GmbH are joined in a very successful cooperation for many years now. Therefore they already completed a lot of promising dosing tests together.
The interview about dosing WACKER thermal paste:
Franz Kamhuber: What is the range of application for WACKER thermal paste? How do they compete with other thermal pastes?
Dr. Markus Jandke: WACKER develops and sells heat-conductive adhesives, gap fillers and pastes as well as silicone-based potting compounds. The applications are very wide ranging. In many cases it is about the cooling of structural components in the field of automotive electronics, power electronics and e-mobility. The products of the SEMICOSIL® TC series are characterized by their high thermal conductivity and the lowest thermal resistance – combined with maximum processability (ease of flow and compressibility).
Franz Kamhuber: How is the typical structure (chemically/mechanically) of a WACKER thermal paste? How high is the share of solids in your products?
Dosing examples: Bead dosing of WACKER thermal paste for the electronics industry
Dr. Markus Jandke: A heat conductive silicone typically contains one or more fillers and some silicone. Whilst pastes generally do not crosslink the silicone, adhesives do crosslink and build up chemical adhesion to the substrate (usually after heat curing). Gap filler, however, cures at room temperature, remains significantly softer and maintains permanent thermal contact through fixation or compression.
In order to ensure the range of properties as well as the processing properties, fillers and their properties have to be specifically adapted to innovative silicone formulations.
The proportion of filler in weight is very large, especially in the area of highly heat-conducting products, since the filler particles must touch each other in order to be able to efficiently transfer heat – this can only take place at a certain density (percolation).
Franz Kamhuber: Could you describe the dependency between the abrasiveness and the functionality of the thermal paste?
Dr. Markus Jandke: The filler particles must be in contact in order to transfer heat. Conventional technically and economically interesting filler systems are based, for example, on oxidic structures which in some cases have a high hardness. Since there is a wide range of different particle geometries – from spherical to plate-shaped with sharp edges – there are also differences in the area of abrasiveness. Here, the filler content or “lubricating effect” of the silicone also plays a role.
Franz Kamhuber: What are the main challenges when it comes to the application of your products? According to your experience where are the limits with respect to dosing?
Dr. Markus Jandke: As electrical power densities continue to grow in the area of many electronics applications, more and more heat energy needs to be dissipated from ever smaller areas. Even if structural components are cooled directly, heat coupling with ever more powerful products must be ensured. A further increase in the proportion of filler – which would be necessary in order to increase the thermal conductivity – would, however, lead to a reduction in the flow properties (viscosities, flow limits) and thus processability. SEMICOSILE® TC is therefore the result of intensive research and product development.
Franz Kamhuber: From your perspective how relevant is the collaboration with dosing experts? How would you characterize the close cooperation with ViscoTec?
Dosing examples: Bead dosing of WACKER thermal paste for the electronics industry
Dr. Markus Jandke: Due to the direct effect of filling properties and silicone elements on the dosability, support from the development team, to ensure the perfect dosability, is essential.
On the one hand WACKER is using laboratory equipment, yet on the other hand, for the intended launch of a new material, it is essential that the dosability has been tested thoroughly on industrial-sized equipment. Only in this way can the future customer be sure that his process is working. With ViscoTec, we have a long-term partner at our side, which is distinguished by its high level of competence, market acceptance and flexibility, especially in the field of dosing thermally conductive silicones. Tests at ViscoTec have confirmed the outstanding processability of our SEM TC products.
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