Munich-based Wacker chemicals group has developed a thermally conductive adhesive for electronics applications. This new silicone rubber, SEMICOSIL 975 TC, is characterized by high thermal conductivity and good flow and processing properties. According to Wacker, light pressure is enough to form an ultra-thin adhesive layer between the contact surfaces. This ensures not only good bonding, but also optimum heat dissipation by the heat sink. SEMICOSIL 975 TC is designed for forming thermal and mechanical connections in power electronics components or packages.

SEMICOSIL 975 TC is an addition-curing silicone rubber that cures at temperatures above 90 °C. The one-component adhesive is electrically insulating and adheres to many of the substrates used in electronics. One of its key characteristics is its high thermal conductivity of 4.3 W/mK (as per ASTM D5470). It also offers good processability, despite the fact that it has a high filler content which is necessary to achieve the requested thermal properties. Before it cures, SEMICOSIL 975 TC is a very pasty, non-sag material that becomes progressively free-flowing with increased shearing. This property can be precisely adjusted to processing requirements. As a result, SEMICOSIL 975 TC can be fed at low pressure, and applied as a bead. It can be processed directly from the pail or from a regular cartridge.

The rheological flow properties of SEMICOSIL 975 TC also offer advantages for further processing. When a part is pressed in place, the applied silicone forms an ultrathin adhesive layer which conforms to the substrate surface without the need to apply high force. The minimum layer thickness (bond line thickness) that can be applied is between 90 and 100 micrometers, with its usability depending on the design of the interface. The adhesive layer compensates for microscopic irregularities in the surfaces, thereby maximizing the contact area and – thanks to the product’s high thermal conductivity – optimizing heat dissipation.