Full Power: Thermally Conductive Adhesive for Air Conditioning Power Electronics

Full Power: Thermally Conductive Adhesive for Air Conditioning Power Electronics

Sitronic relies on DELO

Air conditioning systems are required to cool off cars heated up in the summer within a short time, to dehumidify the air in the autumn rain, and to provide heat within a few minutes during winter. This means heavy work for the controllers of their fan motors, which are installed in the air duct or the motor mount. Thermally conductive adhesives make an important contribution to this work.

Sitronic is one of the leading suppliers of power electronic components such as blower controllers. The automotive electronics specialist's portfolio also includes control and operating systems, lighting technology, and sensors, such as dew point and windshield temperature sensors to prevent fogging. From its development and production sites in Gärtringen and Gunzenhausen and its representative offices in the USA, South Korea, and China, the medium-sized family-owned company not only supplies tier-1 suppliers such as Denso and Valeo, but also OEMs such as Volkswagen, BMW, and General Motors as well as the agricultural machinery manufacturer Claas.

Small Heat Sinks Through Thermally Optimized Design

Much current must flow through the blower controllers, which are partly fitted without screws, to ensure they deliver the required performance: Sitronic offers various performance classes with load currents between 18 A and 35 A; the voltage is either 12 V for passenger cars or 24 V for commercial vehicles. Since space in cars is scarce, the company relies on compact heat sinks. Given the heat accumulation in a small space, a thermally optimized design is crucial.

An optimized heat dissipation can be achieved here through thermally conductive bonding between the printed circuit board and the heat sink. Sitronic had therefore been looking for an adhesive with particularly good thermal conductivity. Resistance to peak temperatures of up to 160 °C and good adhesion to the copper inlays of the PCB and to the die cast aluminum heat sink were additional requirements. And what's more, the adhesive had to be suitable for joining the heat sink and the housing made of high-performance PA66 GF30 plastic material.

The specified adhesive properties in terms of thermal conductivity, temperature resistance, and adhesion were tested in a thermal cycling test with 12,000 cycles and temperatures varying from -30 °C to + 125 °C , a shaker test, and a final function test regarding heat dissipation.

Blower controllers for air conditioning systems: The more compact the design, the better the heat dissipation must be (Figure: Sitronic)

Numerous Benefits in Processing

Following these three suitability tests with different products, Sitronic opted for the thermally conductive DELO MONOPOX AD epoxy resin from DELO Industrial Adhesives. This is a robust adhesive, specially designed with more fillers for increased thermal conductivity to meet Sitronic's specific needs. In addition, it provides considerable benefits for efficient processing.

For example, the adhesive can be easily processed as a one-component product, because mixing systems are not required and mixing errors are thus excluded. The adhesive is silicone-free, a property generally desired by the automotive industry in view of the risk of outgassing in downstream processes. Furthermore, the product cures in one process step – for example within 40 minutes at 150 °C – and can be used for both bonds thanks to its universal adhesion. This simplifies plant construction, since only one dispensing system is needed, which can be used for bonding the heat sink to both the printed circuit board and the housing.

Full Power in Production

Sitronic starts its blower controller production by subjecting the components to atmospheric pressure plasma pretreatment. This increases the surface energy of the components and improves the adhesive's adhesion. Immediately afterwards, the adhesive is dispensed through an eccentric screw valve. The components are joined before the adhesive finally cures in an air convection oven.

The tunnel oven used ensures high throughput and efficient production. Sitronic can thus achieve the high volumes required to serve the numerous OEMs and tier-1 suppliers.