Design considerations for selecting the best thermal interface material

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Thermal Efficiency

The needs of automotive and general electronic devices can vary based on application. In most applications, efficient thermal management is crucial to prolonging the life of the essential electronic components. For example, a heat sink is often used to pull heat away from electronics. But even when pairing a heat sink to the heat source, there is still a thin natural layer of air in between the two surfaces. With the air serving as an insulator, some of the heat doesn’t pass through to the heat sink and the application doesn’t achieve maximum thermal efficiency. In the case of EV batteries, this gap can be anywhere from 1-3mm due to packaging requirements. Thermal efficiency is further reduced in these applications. 

A Thermal Interface Material (TIM) such as gap fillers, are used to maintain seamless contact between the substrates without air gaps and thus maximizing thermal efficiency. Silicone gap fillers are an excellent choice as TIM due to its soft elastomeric properties and the reduction of stress on electronics board. The softness also allows for the materials to compress during vibration. 

While the thermal conductivity (TC) of a TIM material is a critical performance characteristic for heat dissipation, it is not the only factor for efficient heat transfer. Bond line thickness (BLT) or the gap between the heat source and heat sink, is another factor. The lower the BLT the better, as there is less distance for heat to travel. The TIM’s processing characteristics can also impact thermal efficiency. 

With battery packs, a gap filler is dispensed on top of the cooling plate and the batteries are placed directly on top of it. This isn’t feasible with an on-board charger, where heat needs to be dissipated from the inductor and transformer. There are small spaces where air pockets can become trapped, so a highly flowable thermally conductive material is required. Since thermally conductive materials tend to be heavily filled, the lower the viscosity of the material, the higher the risk, and the heavy filler particles will be unevenly distributed to the bottom. A product like ELASTOSIL® RT 7620 TC has mastered this balance of highly flowable and the ability to maintain its high thermal conductive properties. 

As no two applications are the same, finding the right balance in performance and processing is critical for achieving maximum thermal efficiency. WACKER’s portfolio consists of a broad range of products that can be tailored to match your application needs.

WACKER’s Thermal Management Portfolio

Benefits of weight savings in gap fillers

Consumer electronics are becoming smaller in size while increasing in performance. As a result, more heat is generated with less area to dissipate. Therefore, TIM thermal conductivity requirements are increasing for consumer electronics. Electric vehicle (EV) batteries on the other hand pose a different challenge – the amount of TIM materials used. While consumer electronics may use a few grams or less TIM material, EV batteries can have up to 5 litres of TIMs. TIMs achieve their thermal conductivity through heavy metallic filler materials that are added to the base elastomer and thus can add a significant amount of weight – which could be up to 15kgs for 5 litres. This has a direct impact in the range of the vehicle and more weight requires more energy to propel the vehicle. Manufacturers desire the highest thermal efficiency without sacrificing vehicle range. With WACKER’s new SEMICOSIL® 967x TC series products the best in class weight to thermal conductivity ratio can be achieved. It has all the performance benefits of WACKER’s standard TIM gap fillers, but with less density, meaning lower overall weight.

Light weighting automotive applications require the highest TC but without the weight.

For more information, download the SEMICOSIL 967x series technical paper below, or contact WACKER to learn more about other offerings including the highly flowable ELASTOSIL®RT 7620 TC.

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